Will_Emanuel's M-2 Restoration

[Will_Emanuel]

Hello all, just finished a rather lengthy restoration on an M-2 and wanted to document the process. This unit was quite easy to work on due to excellent service information and disassembly procedures in the service manual; Strongly recommend following Yamaha's instructions for disassembly. I've attached a BOM for all the parts used for my restoration. One note is that the replacement relays I have attached did not work in my unit. I'm unsure if I had received defective relays or if they are just incompatible. I had found photos of someone else using the same relays in their unit with success so I assumed they were compatible.

 

[Will_Emanuel]

Ok, Let's begin.

My particular unit was all original and was in working condition when I received it. First order of business was disassembling the front panel assembly to expose the power supply / meter board.

Once that was out of the way I was able to get a better look at the power supply, which appeared to be in great shape. Wrapping on the capacitors hasn't warped and there was no visible discoloration anywhere on the board.

Next step was disassembling each amp module, which consisted of removing the heatsink screws and flipping the entire assembly upside down sitting on the top of the unit for further disassembly.

After desoldering the input wiring and disconnecting two JST connectors, the pre drive board was removed.

This separator panel was then removed, exposing the drive PCB. The output transistors were then removed before freeing the drive PCB from the heatsink assembly.

This same process was repeated for the left channel. After removing the left amp assembly we are left with this.

One of the upgrades I desired for this unit was new binding posts, as the originals are hard to work with and really only work well with bare wire. My next task was freeing the rear panel so I could make these modifications. Quite a few screws needed to be removed as well as a few wires going to the binding posts and power switch before removing the rear panel.

At this point the output board with speaker relays is now exposed just behind the rear panel.

the input assembly including RCAs, level pots, and ground screw was removed at the same time when removing the rear panel.

Next, the two large power supply filter capacitors were removed from their enclosure on the underside of the unit.

At this point the unit was as stripped down as I needed it to be.

Disassembly complete.

 

[Will_Emanuel]

Next thing I tackled was the rear panel and the binding post modifications. The new posts I used were satin nickel WBT knockoffs from parts express. There is very little clearance for terminal depth inside the unit, so the new binding posts would need to be cut down to size. I first started by drilling out larger holes to accommodate the new posts.

A small notch was made on the top of each hole to allow for the notch on the plastic insulator on the new binding posts to prevent them from rotating under load. Next, the new posts were cut down to size one by one.

I used ring terminals for attaching the new output wiring to the new posts. these wires were crimped and soldered into place. After this, the new binding posts were installed.

That wraps up the binding post upgrades. Now back to the rest of the amp.

 

[avionic]

I'm unsure if I had received defective relays or if they are just incompatible.

What is wrong with the new MY2 relays ?

 

[Will_Emanuel]

First to tackle was the power supply board. All electrolytics were replaced, VD1212s Swapped, pass transistor replaced and all trimmers replaced as well.

Amp boards were next. When I first removed them, I again found very few signs of use. No visible discoloration or any other signs of heat.

On the drive board, The bias trimmer was replaced, one electrolytic cap and four mylar caps were changed, all fusible resistors were replaced with modern metal film equivalents, and the VD1212 was replaced.

Similarly on the pre drive board, all trimmers and electrolytics were replaced, yamaha brand mylars replaced with modern panasonic polypropylene caps, VD1212s replaced, and drivers TR221 and TR225 replaced with modern ON Semi equivalents.

Same changes were made to the right channel boards as well. Next, my attention was brought to the output board. Here the two yamaha mylar caps were replaced with panasonic polypros and the output relays replaced with new Omron equivalents. NOTE these relays were installed backwards in this photo. These relays work fine in this unit when the orientation is flipped.

The new Nippon Chemi-Con Filter caps were then installed.

 

[Will_Emanuel]

What is wrong with the new MY2 relays ?

No clue. neither of them click over when I would toggle the speaker switches. I didn't look into them after quickly finding that using the originals solved the issue. I'll hopefully look back into it once I get a chance.

 

[avionic]

You have them installed upside down..... pin 13 and 14 are the coils..

 

[Will_Emanuel]

Next the new output wires were soldered to their respective locations on the output board and the rear panel was reinstalled.

The RCA input board was then reinstalled

Before reassembling the amp, both heatsinks were given a bath in the sink to get all cleaned up for reinstallation

Along with this, the output devices were also all cleaned up and old thermal compound was removed in preparation for reinstallation.

Next, the driver board was mounted to the clean heatsink and the output devices were installed with fresh micas and thermal compound.

Next the metal separator and pre driver PCB were reinstalled.

At this point the input wires were reattached and that concluded the left channel amp reassembly.

The same process was repeated for the right channel amp assembly.

Lastly, the various ring terminals leading to the power supply and amp boards were reattached to the new filter caps.

Finally the front panel assembly was reinstalled and then it was time for first start and calibration.

All clear on the first start this time around, no issues other than the strange behavior with the new MY2 relays not engaging.

After spending quite a while dialing in the calibration, I brought down the matching C-2A I previously restored for a first listen.

And we are done! Everything is now sorted and the M-2 Lives again!

After spending a few days with it in my main system and needles to say I'm quite happy with it. I hope you all find this thread useful!

 

[Will_Emanuel]

View attachment 2632487

You have them installed upside down..... pin 13 and 14 are the coils..

Bingo! must've completely missed my reference. Thanks Avionic!

 

[avionic]

Over all ..Job well done.

 

[Asmodeus2112]

That is beautiful specimen of an M-2. Nice work, thanks for posting, I enjoyed reading this.

 

[Mark B]

Nice work. The M-2 is a sweet amp.

 

[rottalpha]

Lookin’ good

 

[Ren_]

Hahaha literally can see you got ore lazy when you post more pictures. Nice job my friend.

 

[maxchau]

By changing the binding posts to KLEI one will realize the full potential of the M2