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Need help after stupid mistake with Yamaha M60

Garfield

Garfield

Member
Hello everyone!

After a big stupid mistake i got to repair my Yamaha M60.
I did replace four 2SC2581 and the two of that channels driver-tranistors.

I also replaced both rectifiers.

The problem is, that my in-series Bulb always stays lit. Even without Rail fuses. Only without the rectifiers the Bulb goes dim and the VU Meter turns on. I cant find any short on the PSU board.
(Also w/o filter caps the lamp stays lit)
Do you know what i should look for now?

Kind Regards
Pat
 
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Garfield said:
Hello everyone!

After a big stupid mistake i got to repair my Yamaha M60.
I did replace four 2SC2581 and the two of that channels driver-tranistors.

I also replaced both rectifiers.

The problem is, that my in-series Bulb always stays lit. Even without Rail fuses. Only without the rectifiers the Bulb goes dim and the VU Meter turns on. I cant find any short on the PSU board.
(Also w/o filter caps the lamp stays lit)
Do you know what i should look for now?

Kind Regards
Pat
Click to expand...
As far as I know, the design of that amp does not allow the use of a bulb in series.
I had the same issue as yours and ended up taking the plunge by plugging it directly into the mains.
Luckily, it worked fine.
I think mine was an M50.
 
Are the fuses on the rails? Looks like they are on the transformer secondary going to the low rail bridge only. So pulling fuses would only isolate the low rail. Can you confirm?
 
thom01 said:
As far as I know, the design of that amp does not allow the use of a bulb in series.
I had the same issue as yours and ended up taking the plunge by plugging it directly into the mains.
Luckily, it worked fine.
I think mine was an M50.
Click to expand...
I think the M40/60/80 have a more conventional type of power supply, not the x power or whatever it's called on those.
 
X-Power supplies don't play well with DBT's (M-50/70).

M-40/45/60/65/80 & 85 should be fine with the DBT.
 
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Garfield said:
I did replace four 2SC2581 and the two of that channels driver-tranistors.
Click to expand...
What did you replace them with? Why did you replace them? Only two are output transistors. The other two are APS rail switching transistors.

Output transistors should be replaced with complementary pairs. 1-NPN(2SC) and 1-PNP(2SA).
 
Thank you for all of your inputs. I did also check the diodes at the main filter caps and they were okay.
The picture shows the (original) defective devices.
I did replace them with same type replacements (in fact only the bottom two were blown and the smaller driver tranistors - the upper two 2SC2581 were low in HFE (45)).
1000025592.jpg
 
I got them from reichelt. ISC Semi. I know not the best, but i did check them with a transistor-tester and selected the best 4 out of 10.
 
I replaced transistor #118 because it was shorted.
Now the bulb goes very dim, but the amp stays in protect and two resistors (or coils?) get very warm, above 120°c.
The negative speaker terminals as well as the negative main filter cap-pins (the high voltage ones) do also have a short to ground. But i can not find it :/

That also happens when i remove the four 2sc2581's
 

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I do not have a 100W bulb. I tried it direct from the outlet. The two marked 1k resistors just got hot faster and a 100 ohm resistor got so hot, it is open now. At the moment i only have a 5w 150ohm resistor. When i test it now with the bulb (wich doesnt go that dim anymore) the 5w 150 ohm resistor reaches above 100°C before i turn the amp off.
Nothing else gets warm, only those three resistors, but i am not able to find anything shorted nearby...
 
I can mark them on a picture because on those parts there isnt a number printed on the board. The violet circle shows the area where the broken off tip from my test lead fell into..
 

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I really should defer to Avionic, but I think these M series are fairly prone to cascading failure. Meaning, is necessary to check sufficiently far up/down stream to be sure no faulty part remain, or you may well have to start all over again. Hopefully that's properly representing the situation, not exaggerating risk.
 
Garfield said:
I can mark them on a picture because on those parts there isnt a number printed on the board. The violet circle shows the area where the broken off tip from my test lead fell into..
Click to expand...
Those circled resistors are special fusible resistors. You say there getting hot. Smoking hot? Might want to pull them and check their resistance.
If those fusible resistors are getting hot? You have components, downstream, in that circuit that are acting up. ie transistors,diodes,etc.
 
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Yes, smoking hot. The two are 1k, okay. The one on the picture (alone) was 100 ohm but burnt. Got replaced at the moment with 150 ohm because i have to order new ones.
Transistor 118 has been shorted, got replaced but those three resistors didnt care, they still get very hot.
I think i measured all the transistors but non of the rest has been shorted. Since i got a few 2sc2507 (and some b422) i could replace all of them blind. I also got some 2SA1145. But none shows any shorts.
If they blew open, could they also cause the amp to act up like that?
 
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