0:15 Intro 3:57 First look inside 4:35 Tin Whiskers - What are they? 6:15 Taking a look at the schematic 12:18 Checking the power supplies 14:44 Checking power to the amplifier section - Finding a fault in one channel 16:08 Troubleshooting the faulty channel in the amplifier 35:19 Trying the amp out after repairs - We still have more problems! 39:18 More troubleshooting & repairs 40:41 One channel is working, but the other still has issues! 41:28 Finding another faulty transistor 57:46 We have success! 57:58 Silpads vs mica pads - Fear Not! 1:02:34 Adjusting bias and DC balance 1:04:46 Looking at power output and waveform 1:07:45 Looking at the Power supply & speaker capacitors 1:10:49 Replacing some other transistors 1:13:23 Testing & replacing the Filter and Speaker capacitors 1:16:42 Ready for another test drive & closing thoughts
On the other hand, I couldn't wait to bypass the capacitor-coupled power amp stage of my old Sansui AU-555A -- I used a (very early DC-coupled) Kenwood KM-8002 for that job and it improved the sound of my old system tremendously. Fortunately, the Sansui had the requisite preamp out jacks.
I even use ceramic pads for that kind of coolingsomponent, these are more expensive, but they are forever. So everybody using different things to accomplish the same result. Mostly on heavy extern power supply's. Great work again, much appreciated; What I also noticed, on the older amps, the caps are tightened with a clamp, much better than the dirty glue they use these days. Looks more neat.
Great video as usual - thank you! This project turned out very interesting and informative. The troubleshooting part working through the circuit was very helpful to my growing understanding!
The power transformer and capacitor combination can be compared with a compressed air system. The size of the air tank would be analogous to the capacitor, the air compressor would be the transformer. You need a big compressor to keep replenishing the tank. Small refill rate is like filling a swimming pool with a garden hose.
excellent video! I have seen transformer sag before, but not to that level. But on the other hand the power transformer is likely the single most expensive part on the BOM so usually undergoes extra scrutiny. The small power transformer issue is quite common in preamps. So many have a 10-12 watt power trans. Years ago I used to offer upgraded power trans for the Adcom 555 pre, the Apt Holman pre, PS Audio and others. Would usually replace the 10 watter with a 250-400 watt power trans. would have to go outboard, since there was not enough room internally. It was amazing how much more dynamic a pre amp would sound with that big power transformer.
Nice video and great explanation. I have this identical receiver and it had the same problem (I think it was even on the same channel too). As I recall it had a blown output, bad driver and maybe a bad emitter resistor too. BTW this is identical to the Harman / Kardon 330B which Roland Electronics (Rotel) built for H/K. With the covers off looking from above you almost can’t tell the two apart lol!
the metal case is a noise shield. Transistors can be very noisy. The can effect near by components, especially in a low signal circuit. so best replace metal case with metal case
For folks who don't know, there are transistor selection guides in the front section of the nte .....ecg .....sk catalog. So you can pick a sensible choice even if no sub is listed.
While only a tinkler, this is the biggest problem where I usually come unglued trying to replace vintage transistors and not being able to match them up with newer components. I don't also have any of the hard copy books either that you have, which seem very valuable to have on hand. I end up getting too 'rattled' and then unsure what is the right thing to do. Like you said though, this is what you gotta do working on older receivers, and even harder again working on 1960's gear like Reel to Reel tape recorders and early Hi-Fi and replacing germanium to matching silicon replacements.
Hi, great video, I’ve had problems like this with power supplies in older equipment before. As it’s just for myself I tend to run the rail power to a socket on the back chassis and get a decent modular PSU I can pop it in behind the equipment on the shelf. So much good equipment has been let down by the economics of power supplies
I just bought a rtr teac a- 2300s from on online site (not ebay) so I hope it arrives in one piece. I usually don't buy electronic components on line just for this fact.
Tony, note that VAS transistor TR505 can see CE voltage higher than 40V at full volume (especially with no\light load when transformer is not sagging). The new transistor you placed has max rating of 40V CE.
Thanks again, excellent video(s). ,,Those videos with schematics and fault-finding 'thrills',..and trims our nudles (..here do always download and watch same schematic while you talk and probe around ..very enriching-learning-thinkingOfNewThings) ,,Have nice week :)
These videos are really, really good to learn trouble shooting and electronics repair techniques. Concerning the mica and siliconinsulating pads, are the nuts also insulated? What is it to keep the bolt and nut from grounding out the heat-sink?
Excellent Video, very informative. Two questions. First is hypothetical: what would one want to reasearch to replace the transformer as a means to supply more power/ reduce sag? Second: would placing a led circuit inline with the power rail to indicate when the transformer sags be useful or too complicated? Thank you for your knowledge!
I always ask seller to pack carefully before posting and offer to pay extra if required. Maybe the ship hit some bad weather 😁🛥. Obviously ask for partial refund. Great video very interesting. Thank you.
I seen a lot of similarities between this Rotel and the early Harman Kardons from that era. Circuit design, build quality and chassis layout. Even the back panel silk screening looks identical with the layout and fonts. Maybe these Rotels were built at the same factory? Just guessing here. Awesome video Tony, keep up the good work, Cheers
31:36 An alternative partnr for the 2SC538A is the NTE123A (metal housing) or the NTE123AP (plastic housing -> lower wattage) , price is arround 2€ for the metal housing. 48:40 For the 2SC1107, you can use the 2N6123 (Motorola) or the NTE377 as alternative.
There's no excuse for bad packaging. it's nothing to do with cost, it's ignorance. Most sellers who pack badly just can't be bothered to take the time to pack something with care as receivers rarely complain, and as they feel they can just blame the shipping company and claim on the insurance if anything goes wrong. If you're selling something, you include the cost of packing in your postage cost. You can offer additional services when you're selling, but most people don't. Nice work on the receiver.
Hi, i just got a RA-300 and the right channel saturates when i put some volume and im lost. I bought new cables, i tried several speakers including brand new ones, been opening and did the cleaning several times with WD-40, replaced the internal & external fuses and thats all I can do. Im gonna watch your restoration of this unit to see If i can learn something. Thank you very much for all of this. If you have any idea what to check / where to start, let me know. Im about to go to a repair shop in Paris and with your help i maybe able to get what they are gonna tell me they can do and see if their asking price is worth it or over the top. The sound of the 300 is great, i really want to have it fixed. Take care.
Awesome video with good explanation. I do have a question. I purchased a noresco 2660 and I know it was made by Rotel. My concern after watching your video is that every time I Turn the Receiver on or off , it makes a thumping sound and my driver moves inwards super awkwardly. Does that mean a transistor is bad and sending current to my speakers?? Please help/advise. Thanks. Oh, I just subscribed and thumbs up!
Good morning 🌞🌻 Greetings from my humble country 💞 the Philippines 🇵🇭! Research before you make a comment and I love that statement. Have you heard a single ended solid state amplifier? I have a couple of pairs of 16 ohm 96+dB speakers. Have a nice Wednesday!
Like airport luggage handlers...For the most part though I put the blame on the packagers. We ship out dozens of packages a day with our business and have had very few problems with damage or loss through the USPS. I once heard that when you package an item package it so that you can throw it full force at a concrete block wall from five feet. Electronic equipment is the worst to ship, but a little care and thought goes a long way. Styrofoam sheet and double boxing would saved this receiver from that damage.
19:30 I have to disagree with you for your conclusion on where the problem lies but in the end you did come to the right final conclusion. Why do I disagree? If you have 1.8 Volts at the Emitter of a NPN-BJT (NPN Type Bipolar Junction Transistor) then you never can have 24 Volts at the Base of it or it will be blown up in Milliseconds! There is a reverse-Diode path going from Collector to base with Collector being positive to the base, so if collector is positive the diode will pull no current. If you switch off power and do measuring base as positive connection to your diode tester and collector as negative connection then you probably will have a diode voltage drop of 0.5....0.8 Volts. If you have emitter of the transistor sitting at 1.8 Volts and your transistor would be OK then you only could have a base voltage of this transistor of about 1.8V + round about 0.7....1.1 Volts maybe, depending on how hard the transistor will be driven. If you exceed 2 or 3 volts then your transistor will definitely blow up the base-emitter diode path from exceeding base input current. So you can be sure if the emitter is sitting at 1.8 Volts you can more or less be sure either TR506 had been going high ohms or TR508 gone to being just a low ohms resistor ;). Best way to decide where the problem sits would be sucking off (and isolating) both bases of the power-stage transistors and to see if pre-stage and the bias voltage adjustment had gone defective. If it would have gone to round about half of the power supply voltage then pre-stages would have been ok, if it would have been non-symetrically voltage (round about!) to the driver-stage outputs going to power amplification transistors then your driver side would cause the problem.... But nevertheless - you made it and came to the right conclusion and the video shows really good how to isolate the problem and sort out what and where something is going wrong! Good work, and thanks for this video!
I've heard about the tin whiskers and in fact I remember hearing about back in the day NASA had trouble with them in one of the satellites I can't remember which one but I did hear or read about it a long time ago
Maybe you can free up some transformer headroom by switching to LEDs for the lighting? A little here, a little there and you might end up with a job offer from the manufacturer LoL 🤣.... Unless something is drawing more current than it should, especially when being driven hard, I can't really think of anything else that would restore the power output to the original specifications for that amplifier....
Its easier to obtain a decent external modular 48v psu with required power and connect it via a plug at rear of chassis to internal rail. If it just for personal use its no big deal
Thanks for the video. I was just given a Rotel RX-504 and it was working for a while, then all of a sudden the sound signal stopped. The unit is still getting power but the left and right channels are no longer showing watts. Any idea of what could be going on?
4:44 Since arround 2006 they start using lead-free solder in commercial electronic devices, you will see in many years, that the phenomenon "Thin Whiskers" will occur much more again in the future. That was the main reason that lead was added to the solder in the first place to minimize this. Very old electronic devices prior 1940 also didn't have leaded solder, so "Thin Whiskers" is very common with those.
I've heard this contention about lead-free solder from several credible sources, but have never seen it cause any problems with consumer electronic devices.
@@editorjuno , "Thin Whiskers" also not occur within weeks or months, but take many years to develop. Also because they are so thin/small, they are not always visible with the naked eye.
@@BjornV78 -- I'm well aware of that. What I'm saying is that I have yet to encountered an actual consumer electronic device failure traceable to that particular phenomenon.
@@editorjuno , you can't say that for sure, because those Thin Whiskers act like a fuse when they short out, they delete themself if the current is high enough, but the damage as already occured. Also, because these are so thin (few microns),they don't need much current. Also when opening a device,a little knock with a screwdriver against the case can be enough to break the Thin Whisker because they are very fragile. After that you will also don't measure a short that was previous there. And as last, when you gonna troubleshoot a device that has a lot of dust inside, the first thing you do is to clean it with compressed air, that can also remove a Thin Whisker that caused the problem/damage before. They are nasty little things. Grtz
@@BjornV78 -- That's a possibility, I suppose. It seems to me such a tiny strand would be a *very* fast acting "fuse," so I suspect the potential for significant "damage" is fairly small. It also seems to me that if it was major issue, high-density PCBs depending on surface-mounted parts with tiny lead pitches like laptop and tablet motherboards would be failing a lot more often than they actually do, but of course I could be wrong.
When I look at stuff on eBay for sale I automatically consider it to be scrap. So I refuse to pay more than scrap value. I’ve been burned more times than I can count. I don’t care if it looks and plays like brand new at the seller’s house, by the time it gets to my house it’s almost always broken and nearly unrepairable.
Robert Martin, do you mean for finding the open power transistor? You would still have to check the junction with a meter, so I don't see an obvious advantage.
Would you mind sharing more resources for schematics and service manuals for some of these older pieces. I know HiFi engine is fantastic, however I have difficult success finding a lot of the higher end stuff. Last was a tube driven AMC CD player. My email was ignored by amc. I fixed the player, however it would be nice, as you know, to have had the tuning specs.
I wish I could give you some sage advice on finding service documentation, but beyond the normal online haunts (such as hifiengine) I just end up mostly google searching for the documents I need. Sometimes you can find original or copied manuals for sale on eBay or Sams photofact website. You can also contact other service people through various forums and they can share the info with you. I hope that helps.
Tin whiskers are *dendrites*, not "dendrils". Tin pest is another name for the unstable molecular/atomic nature of pure tin, which is exacerbated by extreme cold as well as heat, and has caused failures of church pipe organs in Northern Europe, and NASA satellites, and even contributed to the failure of an Antarctic expedition when fuel cans sealed with tin solder leaked. (Adding lead stabilizes the tin, which is why we prefer leaded solder for electronics use). There are several UA-cam channels with videos about curing tin whiskers inside germanium transistors and Hammond Organ tone wheels. By the way, since tin is considered a vital, strategic metal, the Federal government keeps a stash of it at Fort Knox, inspects it regularly, and melts it down and recasts it every so often.
As I said in the video, there is no drop at all in the mains supply into the transformer. There is a significant drop at the output of the transformer. This is because the transformer is unable to provide adequate current to keep the filter capacitor charged under full load.
@@xraytonyb It wasn’t clear to me from your statement that you depended on your input protection device’s meter or measured the voltage at the transformer terminals. I was just thinking. Given the specs, the manufacture grossly overstated the unit’s capability and used too small a transformer as you stated. Or possibly there are drops in wiring path connections, power switch, or bad output rectifier diodes.
Heavy duty bubble wrap (large bubbles) and multiple layers wrapped tightly in all sides, with a large heavy duty cardboard box (to take the extra layers of packing) is literally not expensive. eBay packers aren't cheap, they are lazy. Large bubble packing wrapped multiple times around to give at least 5 inches of protection on all sides is cheap to do. All these you can pick up at your local UPS store.
I noticed the amp uses a Center tapped full wave rectifier in the power supply circuit, It is a known fact that Full wave bridge rectifier have better transformer power utilization, i.e. less transformer loses compared to center tapped bridge configuration, as you sowed, this power supply displays considerable sag at higher output levels, it should be fairly easy to undo the transformer center tap and substitute a full wave bridge rectifier to see if power supply efficiency improves?
@NICK And how do you do that? If you're using a full-wave bridge rectifier you will overload the wires of the transformer. They're calculated to withstand only the current the transformer delivers on *one* half-wave. If you're using both then they will overheat and you're sacrifying your transformer for just a bit of (theoretical) efficiency improvement. And the other half of your transformer will be out of business totally, as if you would use both windings you would exceed the input voltage into your power circuits. PLUS: if the core of your transformer isn't able to transfer more energy it will tend to go nearby saturation. It can only deliver a certain portion of energy and that's it. And that is what causes the "sag". It's the physical limitation of your transformer. Not of the diodes of your "full-bridge-rectifier", not the gap inbetween the output voltage half-waves on one side of the transformer. It's the core plus the gage of the wire.
doesn't take too much effort to protect the unit, just find a thick cardboard box cut 2"width double the length required, and long enough to cover the side of the unit and 3" inches top and bottom, folder the card in half bend the card in semi-circle so it sticks out about an inch just type it. x8 to the side of the corners front and sides and back. use gaffer tape not duct tape it doesn't leave residue it's not a decoupling capacitor it's a coupling capacitor should get rid of. a decoupling capacitors when it goes to to ground. try transistor. c,o,m, will give you alternatives. just had a look and the 2sc 1108 by isc, is compatible and is better
2sc1107, I have a Claricon Quad receiver that uses them!. Yes, Claricon, NOT Clarion. Mine.are.actually Sanken brand. The xref i found was 2N6123. Lots of searching... I think Mouser or Digikey still has them., I have a thread over on the Nuts-n-Vokts forum. Just search for Claricon.
0:15 Intro
3:57 First look inside
4:35 Tin Whiskers - What are they?
6:15 Taking a look at the schematic
12:18 Checking the power supplies
14:44 Checking power to the amplifier section - Finding a fault in one channel
16:08 Troubleshooting the faulty channel in the amplifier
35:19 Trying the amp out after repairs - We still have more problems!
39:18 More troubleshooting & repairs
40:41 One channel is working, but the other still has issues!
41:28 Finding another faulty transistor
57:46 We have success!
57:58 Silpads vs mica pads - Fear Not!
1:02:34 Adjusting bias and DC balance
1:04:46 Looking at power output and waveform
1:07:45 Looking at the Power supply & speaker capacitors
1:10:49 Replacing some other transistors
1:13:23 Testing & replacing the Filter and Speaker capacitors
1:16:42 Ready for another test drive & closing thoughts
25 watt cap coupled & center tap transformer, should sound really nice! My freshly rebuilt Sansui AU555 is very similar, love the sound of these.
On the other hand, I couldn't wait to bypass the capacitor-coupled power amp stage of my old Sansui AU-555A -- I used a (very early DC-coupled) Kenwood KM-8002 for that job and it improved the sound of my old system tremendously. Fortunately, the Sansui had the requisite preamp out jacks.
I even use ceramic pads for that kind of coolingsomponent, these are more expensive, but they are forever. So everybody using different things to accomplish the same result. Mostly on heavy extern power supply's. Great work again, much appreciated; What I also noticed, on the older amps, the caps are tightened with a clamp, much better than the dirty glue they use these days. Looks more neat.
Thanks for taking the extra time to show the process, not just the results
Sorry, I'm chuckling to myself about your comments about heatsink pedantry whilst I sit back and admire the print and connections on that board!
Great strength building session. Thankyou for the lessons.
So much information in so _little_ time. This is pure gold. Thanks, Tony!
It'd be really cool to put a nice toroidal PT in there! Much more efficient and don't saturate as easily.
This is a really informative and enjoyable electronics lesson. Kudos to Rotel for producing such readable and detailed schematics. Y
Great video as usual - thank you! This project turned out very interesting and informative. The troubleshooting part working through the circuit was very helpful to my growing understanding!
The detailed explanation is brilliant and informative. Thank you.
Hey Tony, happy Sunday to ya brother!
Much love to you and yours.
A cracking video, Tony, so informative, well done Sir...
The power transformer and capacitor combination can be compared with a compressed air system. The size of the air tank would be analogous to the capacitor, the air compressor would be the transformer. You need a big compressor to keep replenishing the tank. Small refill rate is like filling a swimming pool with a garden hose.
excellent video, have a Fisher with a similar output style ,you gave me a few pointers to look for chasing lost voltages etc.
excellent video! I have seen transformer sag before, but not to that level. But on the other hand the power transformer is likely the single most expensive part on the BOM so usually undergoes extra scrutiny. The small power transformer issue is quite common in preamps. So many have a 10-12 watt power trans. Years ago I used to offer upgraded power trans for the Adcom 555 pre, the Apt Holman pre, PS Audio and others. Would usually replace the 10 watter with a 250-400 watt power trans. would have to go outboard, since there was not enough room internally. It was amazing how much more dynamic a pre amp would sound with that big power transformer.
takes power to make Power!
Nice video and great explanation. I have this identical receiver and it had the same problem (I think it was even on the same channel too). As I recall it had a blown output, bad driver and maybe a bad emitter resistor too. BTW this is identical to the Harman / Kardon 330B which Roland Electronics (Rotel) built for H/K. With the covers off looking from above you almost can’t tell the two apart lol!
the metal case is a noise shield. Transistors can be very noisy. The can effect near by components, especially in a low signal circuit. so best replace metal case with metal case
I’ve used both Sil pads and MICA. Agree with you 100%! Sil pads are fine if used properly.
For folks who don't know, there are transistor selection guides in the front section of the nte .....ecg .....sk catalog. So you can pick a sensible choice even if no sub is listed.
Excellent video. Really interesting and informative. Thanks!
I restored a JVC VR-5505 from like 1976. It is only about 12W channel but also has preamp in/out connectors.
the thermal pads are ok. but you forgot to mention the screw grommet.
While only a tinkler, this is the biggest problem where I usually come unglued trying to replace vintage transistors and not being able to match them up with newer components. I don't also have any of the hard copy books either that you have, which seem very valuable to have on hand. I end up getting too 'rattled' and then unsure what is the right thing to do.
Like you said though, this is what you gotta do working on older receivers, and even harder again working on
1960's gear like Reel to Reel tape recorders and early Hi-Fi and replacing germanium to matching silicon replacements.
Hi, great video, I’ve had problems like this with power supplies in older equipment before.
As it’s just for myself I tend to run the rail power to a socket on the back chassis and get a decent modular PSU I can pop it in behind the equipment on the shelf. So much good equipment has been let down by the economics of power supplies
great explanation and experience.❤❤
I just bought a rtr teac a- 2300s from on online site (not ebay) so I hope it arrives in one piece. I usually don't buy electronic components on line just for this fact.
Tony, note that VAS transistor TR505 can see CE voltage higher than 40V at full volume (especially with no\light load when transformer is not sagging). The new transistor you placed has max rating of 40V CE.
Thanks again, excellent video(s). ,,Those videos with schematics and fault-finding 'thrills',..and trims our nudles (..here do always download and watch same schematic while you talk and probe around ..very enriching-learning-thinkingOfNewThings) ,,Have nice week :)
Fully agree! I was literally doing the same now while watching this video. Brilliant stuff Tony. Keep up posting new vids. We all here love them.
These videos are really, really good to learn trouble shooting and electronics repair techniques. Concerning the mica and siliconinsulating pads, are the nuts also insulated? What is it to keep the bolt and nut from grounding out the heat-sink?
What a nice looking receiver. I wonder how it'll sounds when it's done. 👍
Great work...cheers.
Great video!
Xraytonyb your utube videos are awesome 👍👍👍👍👍😎😎👍👍
Excellent. Thank you.
Xraytonyb your Rote Rx _400 streo Receiver is so awesome
Excellent Video, very informative. Two questions. First is hypothetical: what would one want to reasearch to replace the transformer as a means to supply more power/ reduce sag? Second: would placing a led circuit inline with the power rail to indicate when the transformer sags be useful or too complicated? Thank you for your knowledge!
I always ask seller to pack carefully before posting and offer to pay extra if required. Maybe the ship hit some bad weather 😁🛥. Obviously ask for partial refund. Great video very interesting. Thank you.
I have an ECG book (1996) that shows 2SC1107 -> ECG291. Also SAMS 5th edition Semi xref book shows NTE/ECG291 or SK3440.
My cross reference book says, the equivalent for the 2SC1107 are BD243B, BD537, BD951, 2SC3179.
80V, 4A, 25W, 10MHz
I seen a lot of similarities between this Rotel and the early Harman Kardons from that era. Circuit design, build quality and chassis layout. Even the back panel silk screening looks identical with the layout and fonts. Maybe these Rotels were built at the same factory? Just guessing here.
Awesome video Tony, keep up the good work, Cheers
31:36 An alternative partnr for the 2SC538A is the NTE123A (metal housing) or the NTE123AP (plastic housing -> lower wattage) , price is arround 2€ for the metal housing.
48:40 For the 2SC1107, you can use the 2N6123 (Motorola) or the NTE377 as alternative.
Tony, here's a good one to play: *Snake on the Beach - Nico Staf*
There's no excuse for bad packaging. it's nothing to do with cost, it's ignorance. Most sellers who pack badly just can't be bothered to take the time to pack something with care as receivers rarely complain, and as they feel they can just blame the shipping company and claim on the insurance if anything goes wrong. If you're selling something, you include the cost of packing in your postage cost. You can offer additional services when you're selling, but most people don't. Nice work on the receiver.
Hi, i just got a RA-300 and the right channel saturates when i put some volume and im lost. I bought new cables, i tried several speakers including brand new ones, been opening and did the cleaning several times with WD-40, replaced the internal & external fuses and thats all I can do. Im gonna watch your restoration of this unit to see If i can learn something. Thank you very much for all of this. If you have any idea what to check / where to start, let me know. Im about to go to a repair shop in Paris and with your help i maybe able to get what they are gonna tell me they can do and see if their asking price is worth it or over the top. The sound of the 300 is great, i really want to have it fixed. Take care.
Awesome video with good explanation. I do have a question. I purchased a noresco 2660 and I know it was made by Rotel. My concern after watching your video is that every time I Turn the Receiver on or off , it makes a thumping sound and my driver moves inwards super awkwardly. Does that mean a transistor is bad and sending current to my speakers?? Please help/advise. Thanks. Oh, I just subscribed and thumbs up!
Tony, you need a spill resistant tea cup. that iced tea is terrifying me. I have spilled coffee a few times, no fun.
It adds character to the bench ;)
Good morning 🌞🌻
Greetings from my humble country 💞 the Philippines 🇵🇭!
Research before you make a comment and I love that statement. Have you heard a single ended solid state amplifier? I have a couple of pairs of 16 ohm 96+dB speakers. Have a nice Wednesday!
Open base-emitter is a classic failure of the TO-220 package.
hi tony , just as important as packaging is the careless delivery workers that abuse the parcels.
Like airport luggage handlers...For the most part though I put the blame on the packagers. We ship out dozens of packages a day with our business and have had very few problems with damage or loss through the USPS. I once heard that when you package an item package it so that you can throw it full force at a concrete block wall from five feet. Electronic equipment is the worst to ship, but a little care and thought goes a long way. Styrofoam sheet and double boxing would saved this receiver from that damage.
19:30 I have to disagree with you for your conclusion on where the problem lies but in the end you did come to the right final conclusion. Why do I disagree? If you have 1.8 Volts at the Emitter of a NPN-BJT (NPN Type Bipolar Junction Transistor) then you never can have 24 Volts at the Base of it or it will be blown up in Milliseconds! There is a reverse-Diode path going from Collector to base with Collector being positive to the base, so if collector is positive the diode will pull no current. If you switch off power and do measuring base as positive connection to your diode tester and collector as negative connection then you probably will have a diode voltage drop of 0.5....0.8 Volts. If you have emitter of the transistor sitting at 1.8 Volts and your transistor would be OK then you only could have a base voltage of this transistor of about 1.8V + round about 0.7....1.1 Volts maybe, depending on how hard the transistor will be driven. If you exceed 2 or 3 volts then your transistor will definitely blow up the base-emitter diode path from exceeding base input current. So you can be sure if the emitter is sitting at 1.8 Volts you can more or less be sure either TR506 had been going high ohms or TR508 gone to being just a low ohms resistor ;).
Best way to decide where the problem sits would be sucking off (and isolating) both bases of the power-stage transistors and to see if pre-stage and the bias voltage adjustment had gone defective. If it would have gone to round about half of the power supply voltage then pre-stages would have been ok, if it would have been non-symetrically voltage (round about!) to the driver-stage outputs going to power amplification transistors then your driver side would cause the problem....
But nevertheless - you made it and came to the right conclusion and the video shows really good how to isolate the problem and sort out what and where something is going wrong!
Good work, and thanks for this video!
I've heard about the tin whiskers and in fact I remember hearing about back in the day NASA had trouble with them in one of the satellites I can't remember which one but I did hear or read about it a long time ago
Internally it looks just like HK 330, opinion?
Maybe you can free up some transformer headroom by switching to LEDs for the lighting?
A little here, a little there and you might end up with a job offer from the manufacturer LoL 🤣....
Unless something is drawing more current than it should, especially when being driven hard, I can't really think of anything else that would restore the power output to the original specifications for that amplifier....
Its easier to obtain a decent external modular 48v psu with required power and connect it via a plug at rear of chassis to internal rail. If it just for personal use its no big deal
Thanks for the video. I was just given a Rotel RX-504 and it was working for a while, then all of a sudden the sound signal stopped. The unit is still getting power but the left and right channels are no longer showing watts. Any idea of what could be going on?
Merry Christmas BTW!
what about a MJ3055
4:44 Since arround 2006 they start using lead-free solder in commercial electronic devices, you will see in many years, that the phenomenon "Thin Whiskers" will occur much more again in the future. That was the main reason that lead was added to the solder in the first place to minimize this. Very old electronic devices prior 1940 also didn't have leaded solder, so "Thin Whiskers" is very common with those.
I've heard this contention about lead-free solder from several credible sources, but have never seen it cause any problems with consumer electronic devices.
@@editorjuno , "Thin Whiskers" also not occur within weeks or months, but take many years to develop. Also because they are so thin/small, they are not always visible with the naked eye.
@@BjornV78 -- I'm well aware of that. What I'm saying is that I have yet to encountered an actual consumer electronic device failure traceable to that particular phenomenon.
@@editorjuno , you can't say that for sure, because those Thin Whiskers act like a fuse when they short out, they delete themself if the current is high enough, but the damage as already occured. Also, because these are so thin (few microns),they don't need much current. Also when opening a device,a little knock with a screwdriver against the case can be enough to break the Thin Whisker because they are very fragile. After that you will also don't measure a short that was previous there. And as last, when you gonna troubleshoot a device that has a lot of dust inside, the first thing you do is to clean it with compressed air, that can also remove a Thin Whisker that caused the problem/damage before. They are nasty little things. Grtz
@@BjornV78 -- That's a possibility, I suppose. It seems to me such a tiny strand would be a *very* fast acting "fuse," so I suspect the potential for significant "damage" is fairly small. It also seems to me that if it was major issue, high-density PCBs depending on surface-mounted parts with tiny lead pitches like laptop and tablet motherboards would be failing a lot more often than they actually do, but of course I could be wrong.
Hi I have this unit and it gets really hot on the back plate minutes after its it powered on...could this be failing caps?
Probably a biasing issue. Do not use it until it has been repaired or it will probably blow up.
When I look at stuff on eBay for sale I automatically consider it to be scrap. So I refuse to pay more than scrap value. I’ve been burned more times than I can count. I don’t care if it looks and plays like brand new at the seller’s house, by the time it gets to my house it’s almost always broken and nearly unrepairable.
so it's kind of like buying a Chrysler product ?
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Tips: Use Oscilloscope to Troubleshooting ( MUCH FASTER :)
Sometimes it's good to go back to basics and learn how to troubleshoot a circuit without a lot of test equipment. :)
Robert Martin, do you mean for finding the open power transistor? You would still have to check the junction with a meter, so I don't see an obvious advantage.
Would you mind sharing more resources for schematics and service manuals for some of these older pieces. I know HiFi engine is fantastic, however I have difficult success finding a lot of the higher end stuff. Last was a tube driven AMC CD player. My email was ignored by amc. I fixed the player, however it would be nice, as you know, to have had the tuning specs.
I wish I could give you some sage advice on finding service documentation, but beyond the normal online haunts (such as hifiengine) I just end up mostly google searching for the documents I need. Sometimes you can find original or copied manuals for sale on eBay or Sams photofact website. You can also contact other service people through various forums and they can share the info with you. I hope that helps.
@@xraytonyb thanks
Tin whiskers are *dendrites*, not "dendrils". Tin pest is another name for the unstable molecular/atomic nature of pure tin, which is exacerbated by extreme cold as well as heat, and has caused failures of church pipe organs in Northern Europe, and NASA satellites, and even contributed to the failure of an Antarctic expedition when fuel cans sealed with tin solder leaked. (Adding lead stabilizes the tin, which is why we prefer leaded solder for electronics use). There are several UA-cam channels with videos about curing tin whiskers inside germanium transistors and Hammond Organ tone wheels. By the way, since tin is considered a vital, strategic metal, the Federal government keeps a stash of it at Fort Knox, inspects it regularly, and melts it down and recasts it every so often.
Are you sure its the transformer thats causing the sag?
As I said in the video, there is no drop at all in the mains supply into the transformer. There is a significant drop at the output of the transformer. This is because the transformer is unable to provide adequate current to keep the filter capacitor charged under full load.
@@xraytonyb It wasn’t clear to me from your statement that you depended on your input protection device’s meter or measured the voltage at the transformer terminals. I was just thinking. Given the specs, the manufacture grossly overstated the unit’s capability and used too small a transformer as you stated. Or possibly there are drops in wiring path connections, power switch, or bad output rectifier diodes.
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Originals came from Hitachi. Fairchild replacements ;)
I always run into Mica Pads that are so damn brittle
Heavy duty bubble wrap (large bubbles) and multiple layers wrapped tightly in all sides, with a large heavy duty cardboard box (to take the extra layers of packing) is literally not expensive. eBay packers aren't cheap, they are lazy. Large bubble packing wrapped multiple times around to give at least 5 inches of protection on all sides is cheap to do. All these you can pick up at your local UPS store.
I noticed the amp uses a Center tapped full wave rectifier in the power supply circuit, It is a known fact that Full wave bridge rectifier have better transformer power utilization, i.e. less transformer loses compared to center tapped bridge configuration, as you sowed, this power supply displays considerable sag at higher output levels, it should be fairly easy to undo the transformer center tap and substitute a full wave bridge rectifier to see if power supply efficiency improves?
@NICK And how do you do that? If you're using a full-wave bridge rectifier you will overload the wires of the transformer. They're calculated to withstand only the current the transformer delivers on *one* half-wave. If you're using both then they will overheat and you're sacrifying your transformer for just a bit of (theoretical) efficiency improvement. And the other half of your transformer will be out of business totally, as if you would use both windings you would exceed the input voltage into your power circuits. PLUS: if the core of your transformer isn't able to transfer more energy it will tend to go nearby saturation. It can only deliver a certain portion of energy and that's it. And that is what causes the "sag". It's the physical limitation of your transformer. Not of the diodes of your "full-bridge-rectifier", not the gap inbetween the output voltage half-waves on one side of the transformer. It's the core plus the gage of the wire.
Then the ebay sellers wonder why they get a negative rating and freak out. It's your own fault.
complain to seller and ebay. you will get some money back
doesn't take too much effort to protect the unit, just find a thick cardboard box cut 2"width double the length required, and long enough to cover the side of the unit and 3" inches top and bottom, folder the card in half bend the card in semi-circle so it sticks out about an inch just type it. x8 to the side of the corners front and sides and back. use gaffer tape not duct tape it doesn't leave residue
it's not a decoupling capacitor it's a coupling capacitor should get rid of. a decoupling capacitors when it goes to to ground.
try transistor. c,o,m, will give you alternatives. just had a look and the 2sc 1108 by isc, is compatible and is better
2sc1107, I have a Claricon Quad receiver that uses them!. Yes, Claricon, NOT Clarion. Mine.are.actually Sanken brand.
The xref i found was 2N6123. Lots of searching... I think Mouser or Digikey still has them.,
I have a thread over on the Nuts-n-Vokts forum. Just search for Claricon.