MC2102 - No sound but powers up

[W9TR]

I owned two 2102’s several years ago so I have some familiarity with them.

If you are handy flip the amp on it’s top and remove the bottom plate. Check the following connectors on the power supply board for proper seating, discoloration or other damage: J6, J11, J12.

My guess is that the 6.3Vac contact on J6 has failed. It could also be the GND or 12 .6 Vac contacts. But probably the 6.3Vac contact as that one is stressed the most.

If it is not that, unfortunately it will be the power transformer itself, which will be an expensive repair.

Tom

[eddiel]

Thanks Tom.

I'll have a look this week. I'm handy enough to do that level of checking.

Hopefully it's an easy fix. Even if it's not something I can do I'd like to avoid anything involving, "expensive repair"!

[W9TR]

No worries. My money is on the connectors and not the expensive power transformer. Send pictures when you get the bottom cover off and find the connectors on the power supply board.
Tom

[eddiel]

Will do Tom. Thanks again, to everyone, for the tips. I like this forum

[Msegal]

Good luck with your amp.

I have tried going from tubes back to solid state only to go back to tubes.
You might think you will get the same sound with SS without the hassle of tubes but I was not able to do so.

I might suggest you “double down “ with a second MC2102 to double your power (and your hassle).
No one said this was supposed to be easy.

Best of luck.

Mike S.

[eddiel]

Originally Posted by W9TR

I owned two 2102’s several years ago so I have some familiarity with them.

If you are handy flip the amp on it’s top and remove the bottom plate. Check the following connectors on the power supply board for proper seating, discoloration or other damage: J6, J11, J12.

My guess is that the 6.3Vac contact on J6 has failed. It could also be the GND or 12 .6 Vac contacts. But probably the 6.3Vac contact as that one is stressed the most.

If it is not that, unfortunately it will be the power transformer itself, which will be an expensive repair.

Tom

Hey Tom

J6, J11 and J12 were all seated fine. There was no visible damage to J6. But J11 and J12 were toast. In addition, J12 had some gunk on it that had a distinctive smell of oil. The wires attached to J11 had the same gunk tar like substance on them.

I'll upload a few photos in this thread but if you want to see them all you can d/l them from my dropbox account: https://www.dropbox.com/sh/l3jii9x01...kUHuUsMua?dl=0

When I saw and smelt that tar like substance I got the worst feeling. Perhaps I'm being too pessimistic but it looks like it is actually the transformer that needs to be replaced.

MC2102_J11_02.jpg

MC2102_J11_06 Wires.jpg

MC2102_J12_04.jpg

[eddiel]

Originally Posted by Msegal

Good luck with your amp.

I have tried going from tubes back to solid state only to go back to tubes.
You might think you will get the same sound with SS without the hassle of tubes but I was not able to do so.

I might suggest you “double down “ with a second MC2102 to double your power (and your hassle).
No one said this was supposed to be easy.

Best of luck.

Mike S.

I wish I had room for two MC2012's. There was a time that I did dream of that configuration quite often.

[godwinaj]

Only thing I can see that would be doing that is from the transformers. Looks like something was really drawing some current too. Sorry for the discovery. I feel you pain.

[eddiel]

Originally Posted by godwinaj

Only thing I can see that would be doing that is from the transformers. Looks like something was really drawing some current too. Sorry for the discovery. I feel you pain.

Thank you for the sympathy.

I noticed quite a bit of dust when I opened it up. You can see some of it on the darker parts in the photos. I wonder if that might have been causing some issues.

Bizarre that I didn't hear or smell anything when it happened though. I would've thought something like that would definitely be noticed as it happened

[W9TR]

Eddie,
I may have some good news for you!

Here is the smoking gun. You are holding P6, which is the transformer connector that mates with J6 on the power supply board. Pin 1 is on the left.

Pin 7 has clearly failed. This is the heater supply for V6 and V8, which are the tubes that are not lighting up!

Pin 9 is showing signs of heating and will fail soon if it already hasn't.





Now there is some schmutz in a few places. Here is a picture of J17. There is no high current on this connector and it is at the bottom of the amp so this came from somewhere.


There is also some schmutz on the transformer wires.


Again, these wires are at the very bottom of the amp when it is upright. Now I'm just guessing here, but it is probably some transformer pottting compound. If it smells a bit like tar and it is sticky then that's it. This does not mean that the transformer has failed. It has gotten hot at some point, yes. Pin 7 got very hot, and the copper conductor probably carried that heat into the transformer causing some potting to melt. This is just a hypothesis.

So here's the chase scene for this repair. When you or your service tech call McIntosh, they will not have a service part number for the connector P6 as it is part of the transformer subassembly. It is not repairable.

This is what I recommend you or your tech do:

Thoroughly clean J6 on the power supply board. Pins 7, 8, and 9 carry high current for the tube filaments. Mark the wires from the transformer that go to P6 pins 7,8, and 9. Cut pins 7, 8, and 9 off of P6 using a Dremel tool or something similar. Remove all the plastic around pins 7, 8, and 9 on P6. Unsolder the damaged connector pins, tin the transformer wires, and solder the transformer wires directly to J1 on the power supply board, making sure you have the order correct.

Why is this the correct repair? Pins 7, 8, and 9 carry high current. By soldering them to J6 you ensure a very low resistance connection and eliminate the chance for a future repair.

Finally, clean the schmutz from J17 and P17 and anywhere else you find it. Try 100% Isopropyl alcohol.

Fire it up and if it works you are done. If it doesn't then it is the transformer. But transformers rarely fail.

Thanks to Bob for posting the schmatic, and Eddie the pics told the tale!

Tom