Yamaha M-85 Power Amp Repair Part 1 - Troubleshooting
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- Опубліковано 16 вер 2024
- This is another great power amplifier I recently repaired. It is one of the best power amplifier Yamaha ever made. This unit was defective due to the corrosive glue issue which was a common problem on all Yamaha M-85. Because the complexity of the repair, I have to overcome some challenges included replacing two big capacitors in the power supply. Thanks for the watching and comments.
OK, you have prompted me into finishing the repair of an M-80 I have, belonging to a friend. I'd sort of given up on it, a fellow tech had a go and it blew up twice, but I can see you have to be very thourough in testing the components. Lucky I only have one channel faulty. Thanks for the video.
It will be easier if one channel is still working. That was how I fixed an Accuphase P-300L power amp by using the working channel as the reference.
I have one that the protection circuit is actuated on and won't clear also. Just took the cover off it this morning and a quick visual inspection didn't reveal anything. Will dig a little further tomorrow. I also have the matching C85 pre-amp that stopped working a year or so ago and I just replaced it with a Cambridge Audio 851 N to allow streaming from the web through it. I still want to get the C85 functional again as well but haven't really looked at it yet. Both of them together were extremely nice to listen to. Purchased them in 1988.
Nicely done video.👍 I'm not sure I have the patience to do it. Then to find all the needed parts. Same darn thing made my M-85 fail about a year ago.. A single diode was ate through from that glue used ate the factory. And that cause all 4 of the amp fuses to blow. I had no idea this stuff was corrosive. Took long enough amount of years to wreck my day by eating the metal leads. Lol. Amp could use a refurb but it's pretty costly but worth it as they don't build them like this anymore. So glad I kept my old gear so I had a back up option. Now using the old Fisher studio standard as it has near the power of the M-85.🎼
Thank you for the comments. I am sorry that you have the same problem on M-85. If you still own it and not yet decide how to deal with it, please contact me by email. Address is listed under "Above" in my UA-cam home page.
Looks like a "donor" type of power amplifier, with so many faults. This term is used in repair service for a unit model that serves as a "backup" for repairing other unit models. That means, if something is blown just replace the whole module and put defective back in "donor" unit. It speeds up the repairing time and it's more cost effective for the service technician. Once the unit no longer has a single functional modules, it is being selled for a bargain.
I agreed what you said which it may be not worth to save this amp with such intensive labor. However, it just serves as a hobby which makes my life more fun and enjoyable. Also keep my brain stay mentally sharp with troubleshooting and analyzing the causes of the problem.
You are a True hero!! 👌
Great work
That is a lot problems with that AMP. Hope it was cheap to buy.
How can it be ? so much parts defected ! you're very patient, bravo !
This unit is one of the most complicated projects I've ever repaired. I almost gave up at one point when I found there is a endless problems in main amp, vu meter and (3) power supply circuit boards. It took me almost one and half months to troubleshoot and gather all new parts. However, I have done it just like anybody else. Thanks for the comments.
Hi there!
I bought this power amplifier some 40 years ago and after few years i noticed a problem with it. the left channel volume meters always were lower than the right
hi! any recommendations as to where I can find a legible copy of the service manual for the M-85? The manuals that I am finding online are not clear scanned copies. I contacted Yamaha and they no longer have the service manual. thanks in advance.
Amazing repair, I’m about to dive in and do the same. Why did they have to use corrosive glue....
I assume that the engineers (who designed this amp) didn't know the corrosive glue will have so much impact to their products. In fact, the unit I repaired have more damages than other M-85s. The damage not only started at main amp also extended to all three power supply PCB and VU meter circuit board. I hope this video can help other DIY fans who are planning to repair their M-85. Also thank you for the comments.
@@VintageAudioFan Absolutely, I assume the engineers didn't know at the time :(. I was also thinking of an LED lamp upgrade while inside. How would you recommend cleaning the PCB? I was going to use 99% Iso with an ultra-soft toothbrush. I am hoping the damage is pretty localized, but impossible to tell before digging in. Thanks again!
Why did they have to use corrosive glue? So us DIY repair nerds can buy awesome amps that are in protection mode cheep... ;)
Hi there. Do you happen to know the part number for the four fuses on the power PCB? I noticed that they are four 125v 7a fuses located there. My uncle has a M-85 with blown fuses. He was playing music with both speaker A and B on. I think he overloaded the amp as it suddenly went up in smoke shortly after. I wonder if replacing the fuse will fix the issue. Thanks.
There are two areas may cause the blown fuses: (1) bad power supply (2) defective power transistors. So before you replace fuses, I suggest to check both areas.
Hi, amazing yours video 🥰👍I have a Yamaha M85 amplifier with a defect. It works fine, but you can hear the buzzing of the power supply through the speakers. Can you help me find this problem? :)
It seems something wrong in the power supply. In my video, it showed two big voltage regulator capacitors were defective and I have to replace them. So I suggest to check the components in the power supply circuit first.
@@VintageAudioFan When I have more free time I will try. I will write how I did me. Where are you from?