Відео

Hey why use a jumper wire for D7? Why not just remove it from the board?

Did you need to re bias your amp after?

Now I know why techs hate working on these. Its like a modern car under the hood

Hi. I have the same problem with my amplifier. I opened it and I think the previous owner already fixed it. But I see that the diodes are bonded and soldered together. Is there any chance I can send you pictures and you can help me with the problem? I can't send pictures here. But if you can give me your instagram or some other platform. I send you pictures. Thanks

welp, came back to this video as a reference, only mods I needed to do was the R7/R43 removal...soooo good! Thank you for the videos you do, you're doings Gods work!

Maybi ask what kind of diode and where to buy em… mine has same issue😢

I just had mod #1 done on my 100W 4100 by Jake at Steamboat Amps in Houston and it's like a new amp. The effects loop is still shidt, but direct input (Charvel with a Dimebucker-->$25 Behringer EQ pedal-->Front jack) blows me away compared to factory specs. Still needs something more (don't they always) but high gain B channel is leaps and bounds from where it was.

Thanks. Just fixed mine. Bought cheap from guitar center with that exact issue minus the broken pcb traces

I have had yours 90 watt and sold it and now i have the 35 watt head, the smaller 35 watt sounds so much better and have never had an issue, Ive loaded mine with 1960's RCA EL84 tubes also 1980's shuguang Chinese pre-amp tubes and it sounds wonderful! Also i added a clean foot switch making it a 3 channel amp. Also you can touch the glass with your hands, not when they are hot obviously but it wont hurt them.

So, how have you liked the Amp since? Have you done any other things to it since also? Also, just a couple more suggestions, I've been sort of collecting data on JCM900 mods for awhile, and seems like changing the 250V Bias Cap to a higher value is pretty important. I mean, mines been fine for a long time without it, but I'm planning to do it. Theres like 300 and something odd volts on it, so it's fairly underrated, and a lot of people get bias drift, or it straight up fails. Next, I don't know about the 50W, but on the 4100's, two resistors that are on the board should actually be on the tube sockets themselves. I think R25/R26 on the 4100's. I know that on the 50w because of this, one tube gets slapped a lot harder than the other, and with the 100's, I think it's 2 with the 4100, because I could always tell two tubes were always working harder by the way they looked, so I always rotate the tubes, but this mod will fix all that. Lastly, with the 4100's anyway, I noticed a couple years ago my Power Caps were wired wrong from the factory, and then noticed it in a bunch of them since. The 50w's likely don't have this issue, but just pays to check, but if you ever get a 100w, definitely check. If it's wrong, one half of one of the Caps will not be used. So one will be using the full 100uf of the 50uf/50uf, and the other will just be using one side(50uf).

I have the 4100 dual reverb and I love it. I also bought the IR-X and put it in the return for a pretty much Fiedman Be-100.

Hi, great Video, I use my 4500 HGDR always on 50 watts, no matter what. It's way more punchy at that setting, but it really awakes, dialing the MV-pot past 6 (2 o'clock). Cheers from Münster, Germany Frankie

The repair insyructions explicitly suggest to clip the diode legs and heat them so the remains foll through the holes, you’ll save your self some scorching the traces by following that advice.

Bruh...sick video! I'm picking up a 4500 this week for a trade I'm doing. I am going to do these mods and your video rocks! I have the JVM410H, I wish there were videos of dudes doing some mods on that like yours. Thanks!

Good job man. I had the same bank of diodes in that circuit burn out and burn the board. It's criminal. I have my amp packed right now and being picked up today to send to MESA for repair. It's not inexpensive to ship even the amp section with tubes and cable and footswitch (they want all that) and have it insured. But what are you going to do when you're dealing with a $3000 amp? Fix it if you can, but not having seen the schematic previously, you wouldn't know the jumper order for the diodes.

I had to wade and search trough forums all day long to find out which mods I'd want and hiw to do them. So great video! I also want to point out that the G12T75 speakers aren't the best sounding to go with this amp. Changing to another speaker will be a huge benefit for the sound.

This is a tutorial of how NOT to perform this service bulletin. The damage he has caused to this amp can never be undone short of sending it back to Mesa to have the entire populated PCB replaced. The damage to the traces were 100% the victim of his inexperience and ignorance. After servicing hundreds of different Mesa products over the past 20 years I can say with all confidence this repair can be done, not only without any damage to the pcb, but to the competency that even a trained eye would not be able to detect the work was not done at the factory. Please DO NOT follow his example - take your valued $2k amp to a qualified tech for proper service.

Just bought a brand new mark v it hasnt arrived yet. Starting to have regrets buying it, after hearing about problems and also having hard times having it worked on. Think i may get rid of it on reverb since the store wont do refunds.

bought yesterday a marshall jcm900 2100 cant wait to have it also that ibanez but 7 strings and fixed bridge killlller guitars 11 piece neck etc etc etc just amazing .

People who are unhappy with their 900, 2000, TSL, etc... Before modding or getting rid of your amp, it's always a good idea to experiment with the one thing that influences your tone more than anything.... try different speakers! Speakers and even the cabinet can make a huge difference, especially if you have a matching Marshall cabinet with T75's which many consider flat and/or uninspiring. That or an EQ pedal can bring otherwise "meh" amps to life.

I have a JCM 900DR 100...along with other amps. Like your content and insights, subbed.

The service bulletin recommends clipping the diodes, melting the solder and letting the leads fall through to the chassis. This is to prevent burning and lifting the pads. I am very sorry to post this, but your video comes up #3 on a search for the Mesa Mark 5 diode repair. YOU destroyed those traces and pads with your giant radio shack soldering iron. To make matters worse, your pliers are huge heat sinks necessitating you to put even more heat into the pcb. Please take what I have to say as constructive criticism when I say that what you did here is an appalling hack job.

Get yourself a GT-7025 preamp tube and replace the V1 on that 4500. I promise you will love it! It made a massive difference with my 4500. So much so it raised the hair on my arm as I tried it. I had to put the old one back in to make sure i was hearing what I heard. It went back to sounding like a wet blanket was over my speaker cab. Then it really opened up when putting that 7025 back in. Also do you run the effects loop jumpered when playing? That makes a massive difference with these too!

I didn't like the diode bridge jumper. It muddied it up so I left it in the circuit. C27 jumper added too much muddy low end. I removed the jumper. R7 did nothing to my ears so I left it in. The R43 jumper was the best of his mods. Fattens up midrange nicely. If you want to really thicken up the channel B you need to raise the C9 coupling cap value. Stock is .22uf. I jumpered a .68uf over it. Now the gain channel has nice thump without being muddy. Give it a try u will like it. I alligator clipped different values and settled with the .68. it lets more midrange thru and removes the sizzly upper frequencies. Everybody perceives tone differently but I found the c9 mod a night and day improvement.

Brother get your hands on any old 2204. I'm sure you already know what they're about. They're pure and modding them is sickeningly fun

Good Job !

Have a recent pre-Gibson Mark V-35 that was dropping output less than a year after purchase. Replaced all the tubes with after market, and haven't had any issues for the last few years.

I had one and I think there was a problem with the loop I should've kept it and sorted out the problem oh well

I was able to get under the circuit board by de-soldering only 1 side - you can use needle nose pliers to pinch those little white plastic pegs (they are what keeps the circuit board fastened to the chassis, mostly). They turn, so if you can carefully pinch them and turn them a bit, you can pull the board up enough on the problem side to get under. What a damn hassle this thing is!

♠🍀♥ Thanks for doing this video, the JCM 900 is actually a good amp. I started using these mods three or four years ago but never finished the video. The JCM 900 was a new approach mainly because of the preamplifier with the transistors and some extras that became increasingly popular as mods since the seventies. Not a bad first attempt but there is still a lot that can be improved. Normally I mainly recreate Lemmy's amps, but I did the same thing with my son's JCM 900 and my guitarist's JCM 900. From the factory there are two problems with many of the 100W models that should be eliminated. There is a great video about this, I hope it's okay to post the link here, it might save the lives of some JCM 900s: ua-cam.com/video/xGJ1kMWYAxg/v-deo.html I changed a few other things on my son's JCM 900, but with the preamp it took a lot of time to tune everything so that the different mods fit together, but now it has a lot more low end and power, a real beast, which is also great for Drop D or Drop C tunings. However, playing clean is still possible and the bass can be reduced using the bass control. I converted the power amp section to JCM 800 specs and it was also a good thing to install a choke. Apart from the preamplifier, the 900s are actually classic Marshalls as they have been built since the 60s. Replacing the large filter caps can also make the sound fuller again in older amps, they go bad after 20 or 30 years, especially if the amplifier hasn't been played for a few years and is then immediately put under full load again.. If the amp has been played a lot and loudly, it is a good thing to replace and bias the tubes, then your amp will work like new again. Greetings and best wishes :) 🎸🎛😲

The modded sounded I'm hearing is a little more harsh to me than stock. So hard not being there in person to hear and feel it. But I wonder if harsher sound is fixed with an EQ adjustment. Muffled or blanket-covered sounds can't be made brighter, but brighter amps can always be dialed back even with a tone knob on the guitar (unpopular opinion). I'm just unsure if this video motivated me to try this with my JCM900.

Come on Tinkerbell let's see what you can do

Congrats! Happy with you! May be helpful for me in future , thanks for sharing, great work! That was not easy but you didn't gave up and was worth it 🏋️🤟🎸

Brutal brutal butcher job on this wow !

Should try a quality eq pedal,.... a different cab,... different speakers,...etc. Only thing I run with my JCM 900 50 watt combo is a wah. If I am running pedals,..my Hiwatt.

I wish I still had my dual v every. Best amp I’ve ever owned.

Cool video! Btw consider getting a lav or shotgun mic for your narration track.

Improvements?? Sell it, buy a Plexi replica of one kind or another, buy a reactive load box to tame the volume, crank the volume, throw a boost in front if needed and you will be in amp heaven.

Improvements?? Sell it, buy a Plexi replica of one kind or another, buy a reactive load box to tame the volume, crank the volume, through a boost in front if needed and you will be in amp heaven.

I've had the same amp...since 1990. And I'm very happy with the high gain lead channel! If I want more sound, I'll use my JVM 205. But I don't think it's necessary to modify the JCM 900. Then the beautiful character is gone.

Mod sounds better, more open gain structure, more natural sound, not "choked" sounding like stock. Also less of the crashing chainsaw highs, the highs sound great now.

I will say i to have the Mark V not the combo though, mine did the same thing back in June. Is this known for Mark V’s ? I just bought mine second hand brand new coming on 3 years now

Cool video man. I actually have had the issue with my Mark V… twice. The first time I did not feel confident to perform the repair so I brought the amp to a tech… the second time though I did it by myself no problem at all. Except for some of the PCB traces raised and/or burnt 😂