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Odd M60 Problem

OMGCat!

OMGCat!

Super Member
The other day I found a non-working M60 locally for a very good price (almost free). It looked kind of beat up so I figured it would probably have one smoked channel which would make it a good parts amp as I have an M60 and M65 already.

I got it home, hooked it to a DBT and found it's in protection but the bulb dims normally. I found that someone had done previous repairs to the rectifier board and attempted to wire wrap by hand which resulted in a whole bunch of loose connections.
The main board was absolutely coated in dried soda or some other thick sticky substance.

I could have left it at the and parted it but I figure all the parts are better together and if I can get the amp working then I know I have all good parts. Beside parts I will have another M60 so maybe I can vertically bi-amp my speakers, blah blah, you know the deal already.

Work so far:
Cleaned boards with simple green and flux brush to remove sticky stuff. This took about 45 minutes of brushing but the boards look darn near new.
I repaired the wiring on the power supply.
Removed DSBG and replace three jumpers. I put the old 1000uf caps back even though they are showing around 750uf. If I get it up and running I'll recap it later.
I removed the open frame bias pots due to soda intrusion and found the right channel pot to be showing 1k rather than the usual 500k that these seem to hover around.
I replaced both bias pots.
After that I attempted to power it up and it still won't come out of protection but again, the DBT dims and goes out.
I checked the transistors lined up on the heat sink and found 1 2SA1306 to be shorted on the right channel. Not it's counter part and none of the outputs are showing a short.

Would the low value of the bias pot cause this one transistor to short? What else should I be looking for? I was planning on following along on one of the M60 Chernobyl threads but mine seems to have decided to fail in a new, novel fashion.
I do have the factory manual here so can follow the schematic but thought I might get some input from the experts.

I've ordered replacement transistors from Digikey 2SA1837 and 2SC4793 and am out of town for a few days starting tomorrow but thought I'd get my thoughts primed for what to do when I get back.

Also, aside from the few watts and the ability to shut off the meters, what is the difference between the M60 and M65? They look identical inside.
 
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Check the solder connections on the voltage amplifier transistors. They usually unsolder themselves.
OMGCat! said:
1k rather than the usual 500k
Click to expand...
They are suppose to be 1K ohm bias trimmers.
 
M-60/65 identicle amplifiers. Only difference is the front and rear panel silkscreened print.
 
Thanks for the advice.
I'll give the solder joints a look when I get back to the bench.

I did mean to type 500 ohm rather than 500k. That one pot was at 1k no matter what position it was adjusted to. Seems soaking in sticky goop for years is no good for open frame pots.

Good to know about the 60/65 being the same.
I already have a near perfect example of each that I can bridge with my C-80 or bi-amp with active x-overs so this beat up one can make a good diag project that I may keep around or sell off.
 
Got a little time to check out the amp today and found TR111 to also be shorted as well. Everything else looks to be good but I don't get what would cause only TR111 and TR125 to short. I'm guessing with the power supply board wires making poor/intermittent contact it may have caused transient voltage spikes that eventually took out a few devices.
Also, pretend that I'm kinda dumb and don't understand how this amp works. It appears as though you have the amplifier circuit that uses two PNP and two NPN outputs (per channel) normally and there are two of each that aren't used in that circuit. Are these for class A operation?
I think half of my outputs (all of the ones that are in the normal amplifier circuit) have been changed as on both channels(both SK and both factory numbers) have different silk screening on them while my other two amps have the same silk screening on all of their outputs.

Hopefully will be able to make a little more progress this week. I've got to find a sub for the 2SA1145 now as I've already got a parts order coming so hopefully can find something in my take out pile to use. I think a 2SA1370 should sub in for a while as I've got one on hand. I'll put in a KSA1145 if I get it up and running.
 
OMGCat! said:
Also, pretend that I'm kinda dumb and don't understand how this amp works. It appears as though you have the amplifier circuit that uses two PNP and two NPN outputs (per channel) normally and there are two of each that aren't used in that circuit. Are these for class A operation?
Click to expand...

These transistors are for the X-power supply. There are two voltages per rail, and the amp adjust the power supply's line voltage to the level required by the output stage
 
The extra set of transistors on the heatsink are just for rail switching in the APS circuit.
 
Ok so got a little more troubleshooting done but it's still a weird failure.

Since I knew TR125 was bad (not shorted but no good) I worked my way back and found TR117, 111, 109 and 107 bad as well. None are shorted rather they test open. TR109 had some kind of moment go on because it's missing the rounded part and you can see the junction inside. TR133, 131,103 and IC101 test good. All of the components going to the other pair of outputs from IC101 test good.

Everything else like diodes and resistors check ok. I figure replace all semiconductors (including diodes) after IC101 up to the outputs and then run it up on the DBT with the outputs out and see what happens?
Should I replace just the failed parts and leave the good parts leading up the the other pair of outputs or should it all match before powering it up?

My sub list I think is good as I picked it up mostly from other threads but I wouldn't mind a verification.

C2240 -> KSC1845
A1015-> KSA1015
C2705-> KSC2383?
A1145-> KSA1013? I think I saw a KSA1345 recommended for a sub here but I can't find it on Digikey or Mouser.

HZ16-3L-> http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=207769736&uq=636104245872301107
 
@OMGCat!
Here's my sub list if you want to double check (sorry about the messiness), I think most of those are here.

In my modest experience the subs never have exacting specs - in fact some values are quite far off compared to the originals - so while they probably work fine (and I personally think it's okay to just use them as individual replacements for the purposes of testing and getting the amp working again); I think it's probably a smart idea once the amp is working to replace the matching transistor in the other channel with the same sub, and to also replace the complementary transistors on both channels.

I think it's fine to just replace individual items for the sake of testing / getting it going again though.

2383/1013 are a suitable sub pair (for 2705/1145), 3503/1381 are a better sub according to avionic however keep in mind the latter have a different package and you have to file or sand the legs down a little to fit in. Mouser stocks all of these, but it's probably a good idea to stick to the matching xxxx/xxxx pair in either case.

subs.jpg
Edit - HZ6-CL can be subbed with HZ-6CIL's sub also
 
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Nice, thanks for the sub list. That can come in handy for sure. It's really nice that Yamaha used a lot of the same components in their contemporary lineups.
I also think replacing what is known bad is probably the easiest/best course of action. It would lead to less chances of injecting mistakes into the project as well. Once I know all is well I can go for details I suppose.
I've done refurbs on components in sorry but working condition a few times but this is the first DOA basket case that I've tried to resurrect so being extra cautious.
 
Update on the project.

Got all of the semiconductors between IC101->TR131/133 replaced. TR107, 109, 111, 117, 123, 125 as well as zeners D113 and 117 checked bad. I went ahead and changed all the rest of the diodes and zeners in the area beside D133 as I'm out of 12v zeners but it checked good on my tester.

As it sits right now I've got all of the outputs out with 470ohm resistors subbed in. I powered it up on the DBT and the bulb dims but it's still in protection. I'm getting 57V at the protect relay out of this side of the amp while the good side is floating around 20mV.

After powering it up and seeing that high of voltage at the relay I went after the PS section because it should only have +/-35v at idle.
Working my way into the junctions where all the wires meet had me pull the filter caps brackets and whatnot but I really don't see anything yet. I have proper 35v and 60v going to the main board from the rectifiers and the right amp gets the 35v+/ - like it should while left side seems to be getting +60v and -42v.
Tomorrow is a busy day but I'll have to do some more looking at the schematic to see where things go wrong.

I'll add that this is exactly what I saw before I started work. I didn't think anything of the high voltage at the relay since I really wasn't familiar with the X power supply at the time.
I've also pulled every other transistor on the faulty amp and they all checked good. Same with the diodes (all checked and/or replaced except the big ones buried under the filter caps, I haven't gone after those yet).
 
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OMGCat! said:
I've got all of the outputs out
Click to expand...
Both channels ? Or just the single bad channel ? Which channel has the high dc voltage ? Same channel that you replaced all the parts in? How many output transistors were removed from each channel ?
 
Did you check all the transistors and diodes in the APS rail switching circuit ? Solder connections on the TO-126 switching drivers.
 
I had a similar problem in my M80. It was a faulty transistor in the APS circuit.
 
All outputs have been removed on the bad (L) channel that had the damaged parts, This is the same channel with high DC.
Good (R) channel I've done nothing to.

I pulled and checked just about every transistor and diode in the bad channel but it's obvious I missed something. I've also touched up every joint that looks suspect.
I went through the schematic and it looks like I've already pulled and tested every tr in the APS circuit (TR151 on up). It's possible that one may be leaky at a higher voltage than my checker uses but they all seemed good.
I'm going to have to poke around some more in there and see what I can see.
 
The emitter resistors measure .40 or thereabouts in circuit which seems to be what they normally measure when lead resistance it taken into account. I can pull them and measure out of circuit though. Whatever happened to kill this amp spared the outputs which is nice I suppose.

I did have all four outputs out (with the 470 ohm resistors in their place) with the other APS transistors still installed. After figuring out the voltages were wrong I pulled the APS TRs and checked them (all good).
I've also checked for solder bridges or anything else obvious but either missed it or it's not there.
 
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Does R103 and 107 still look serviceable? No signs of overheating ? If they are burnt its and indication that IC101 is bad.
 
They look fine, I just went and eyeballed them again and they appear ok. I pulled IC101 and both halves check good.
Nothing on the board was burned except TR109 was popped with the curved side being MIA somewhere. It seems like this amp had a Three Mile Island rather than a full Chernobyl.
 
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