Yamaha M-2 R channel out trouble - help needed

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Yamaha M-2 R channel out trouble - help needed PLEASE!! ** Update - Success!

Hey guys, I could really use some extra help on this one.

I have an M-2 with the R channel out.

Question for the gurus; Can I leave the final output transistors out of circuit and test anything so I'm not blowing $20 worth of parts while troubleshooting?


After going through it initially, I ordered enough output devices (on-semi MJ15001/MJ15002) per another suggested thread as replacements for the SA1051/SC2461 (TR509-TR514). Ordered SA1837/SC4793 pairs as replacements for the SA968/SC2238 pairs (TR508/TR507).

It had also dropped TR501, an SA914 so I got some SA1142's (had some SA914/SC1953 pairs, lost them) Everything else seemed (haha) in order. All parts came from Mouser.

I also found a few of the VD1212 (MV12) varistors (D505) and replaced them with series 4148's as a matter of course. There were 2 on the pre-drive board, one on the driver board.

I installed the new new devices, and POOF! Not only did it take out almost all the outputs and TR508 again, but it popped the AC fuse this time. WTF? Although I may have cracked the fuse glass on the bench, who knows.

I went through the amp board a little better this time, pulling all the fusistors and all but one of them (FR503) are open. Not sure if they were the first time around - if I didn't check well enough - I pulled them from the circuit this time to check...

I've checked all the caps parallel to these and they seem OK. I intend to replace all these fusistors now with flameproof resistors of the same value and sufficient wattage and replace TR508 again.

Again, my question is this; can I leave the outputs out of circuit and test anything so I'm not blowing $20 worth of parts while troubleshooting?

Any help with answer, or any other suggestions on this amp are greatly appreciated.

[ edit ] I don't know why this post lost the attachment, but I've re-uploaded it.

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Service Manual

Cheers!
 

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Ooouch..I Hate it when that happens...:dammit: Been there...
 
Update:

Impatient that I am, I briefly powered it up with the outputs removed.

No fuse blowing, hopefully a fluke.

FR505 and FR506 (replaced with resistors) along with TR508 up in smoke once again. Blarg!. I had a 3w 22ohm for FR506, but took a chance on the 390ohm with some 1/2 watters. The others (390 and cobbled 56) survived. Checked all resistors and caps around these and everything checks OK. I'm still hesitant to put any new outputs back in this thing until I get some sage advice. I'm going to go over the last steps using 3w 390ohm(400 is what I can make with parts) and see what happens.
 
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I would not want to power this one up with the outputs simply removed.

I am a proponent of removing outputs to check the health of the front-end, bias string and drivers, but on this one you need to add one more step.

1. Remove the outputs.
2. connect 1k (or so... ....not critical) resistors from the emitters of the
drivers (TR-508/507) to the output line.


This way, the feedback loop is closed and you should get your amp's real DC voltages for offset, etc.
 
another tip. if you're looking for more of the (obsolete) outputs or other transistors for the M-2 after blowing those Onsemi substitutions, try Electronic Expediters out of California. i stumbled across them while looking for genuine original Sanken outputs for my PC5002M. they had them in stock, luckily, and they were basically the same price as the Onsemi subs i almost went with. their minimums were pretty reasonable, too, at least in my case.
 
I am sure you have probably thought of this, but a dim bulb tester would save you some cash and potential frustration. Something is drawing a lot of current, there's no point powering up the unit fully until you find it.
 
One minor update I just hadn't had time to post.

With or without the pre-driver board connected to the driver board, I'm getting 80V on the H and L lines where there should be like 1.9V and 2.9V. However, I'm uncertain if this is valid without the output trans in place. I can't find anything wrong in the circuits/components anywhere in or around the predrive H and L lines. I suspect these are part of the feedback circuit but can't read schems well enough anymore to determine if this is the case. Anyone care to take a gander at the schem and tell me if these are the FB loop?

I'll look at the suggestion of running 1KW [edit] 1k ohm (lol, old Microwave radio tech in me) across the emitter outputs. OK to just run across the first pair only?

I'm concerned the dim bulb DIY variac isn't going to supply sufficient voltages to trigger parts of the circuit. I've heard conflicting views on using this method on some SS amps.

cdfac, thanks for that tip. I'm leery of counterfeit Toshiba's unless I'm told of a good and trustworthy source.
 
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With the driver board in there, you should NOT be getting the big voltages on the "H" and "L" lines. The Bias transistor should be holding that voltage spread down to a couple of volts.. Check the two bias transistors TR-501/502.

You only need one pair of resistors to bypass the outputs and close the feedback loop.
 
501 has been replaced, 502 checked out OK. I'll go ahead and replace both again, FR504 (equivalent), and TR507/508 again as a preemptive measure.

Just so I'm getting this right, I'll connect a 1k ohm resistor load from the emitter of both TR507 and TR508 to the CT output line as indicated in the image below?

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Thanks
 

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Update.

After thinking about it some more, I decided maybe I should be running the emitter output of TR507/TR508 to the respective CT and PE lines, thereby running the bias back through the feedback loop. C501 was pulled and tested, seeming a little "squiffy" insomuch as a 1uf can be tested, so replaced with a 1uf 80V donor part. Having a partial Yammie boneyard comes in handy at times.

Right or wrong, I moved the 1KOhm resistive load to the points indicated and fired it up. TR507 got rather warm, TR508 stayed cold. I figured there's an issue on the TR508 side and did some more checking. I found TR504 open and replaced it.

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Another check with the outputs installed and it popped the fuse. Re-checked the outputs and I lost the TR510/TR513 pair. :tears: Getting rather frustrated, I decided to re-check R516-R521 and found R520 open. Replaced it with a donor from a spare CR-1020 pwr asm and gave the board a good once over. I found some cold solder joints/cracking on some of the output mounts and put them right. I put in my LAST PAIR of outputs and said a little prayer.

Viola! By George, I think I've got it! wohoo, yipee. :banana:

Offset and bias are adjustable to spec and there's sweet, sweet music coming out on the test speaker after running source to input.

Now I just need to run down an issue on the left SPKR-A output, deox the input attenuators, clean her up a little, replace some temp parts with a Mouser order (I cobbled up some of the replacements for the fusistors) and button things back up.

I do have one question. The Micron 5W .47 Ohm cement, board mount resistors seem impossible to find. Anyone have a source? Should I just get axials of the same value and call it done?

cdfac, thanks for the tip on the Toshiba outputs, I'll have to go looking...

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I see alot of transistor replacements and on going failures, if i were you I'd look at your capacitors too, they break down and leak over time. don't overlook this area.
 
I guess I found the problem with the left side A-Speaker output (lack of).

Doh!

This thing took a serious hit. All the damage I had to repair in the R channel, then this...

For the record (and search) the Yamaha M-2 Speaker Relay has the part number TYPE MSJU 12VDC DEC 142 Japan stamped on it.

Pins 13 and 18 are the relay coil
Pins 8 and 12 are the Right Speaker contact
Pins 5 and 9 are the Left Speaker contact

DSC_5894.JPG


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Same pinout as the Omron MY2-02-DC12, but the Omron is only rated at 5A break current (its carry current is at least twice that though). AFAIK, there's no other direct replacement for your relay.
 
Just my quick look, but this is a progressive amp. Your pre drivers 507 and 508 feed 509 and the rest in stages via their base bias resistors. you can safely remove 511 on to save transistors as you have first stage outputs still in the circuit. 509 and 510 provide the overdrive feedback that shorts the input signal through 505 and 506 so as not to hurt the main outs. Although they do that to the stage before the predrivers 507 and 508. Double check 507 and 8 for CE shorts if you are toasting the .47 ohm current limiters on the outputs. I cant see the H L lines on the print, might be missing it on a quick inspection though. .47 ohm 10 W ar Rat shack all day long. It will live, just be patient, takes time to figure these beasts out. Don't know the amp. but guessing about 200W output through the print?
 
Thanks for the responses.

Phaseone, in case it wasn't clear in post #11, I've fixed the amp and it's running great. Just tidying up a few issues like the speaker relay and I've replaced all the fusistors and varistors in the other channel. 250WPC.

EW, thanks. I might have found an obscure source for the relay, Same part used in the pro P2250 amps. waiting for a response. If not, I'll try the Omron MY2-02-DC12 you suggest.
 
If you find a source for the original style (new ones), I'd like to know. Many Pioneer and Marantz use them too.
 
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