Need help after stupid mistake with Yamaha M60

[Garfield]

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

 

[thom01]

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

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.

 

[Dave1027]

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?

 

[whoaru99]

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.

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.

 

[avionic]

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.

 

[avionic]

I did replace four 2SC2581 a

What are the TR #'s that you replaced?

 

[avionic]

I did replace four 2SC2581 and the two of that channels driver-tranistors.

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).

 

[Garfield]

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)).

 

[avionic]

(in fact only the bottom two were blown

Those two are for the APS switching. Where did you get the 2SC2581's?

 

[Garfield]

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.

 

[Garfield]

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

 

[whoaru99]

The negative speaker terminals as well as the negative main filter cap-pins (the high voltage ones) do also have a short to ground.

Unless I misunderstand your comment, speaker negative is common ground.

 

[Garfield]

okay, sorry i somehow thought it isnt ground.

 

[whoaru99]

okay, sorry i somehow thought it isnt ground.

As well as would be the common midpoint of the main capacitors for the (+) and (-) rails.

(+)(-)(+)(-) common ground (+)(-)(+)(-) if that makes sense.

 

[rjsalvi]

How many watts is the bulb you're using in the DBT?

 

[Garfield]

It is a 60 Watt bulb.

 

[rjsalvi]

It may not be big enough for the M60. Try a 100W incandescent bulb. If the bulb isn't enough wattage, the relay may not close.

 

[Garfield]

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...

 

[rjsalvi]

It helps out if you can list the circuit board part numbers for the overheated resistors. They're burning up because the current draw through them exceeds their wattage rating. That's a sign there might be a short somewhere...possibly a faulty transistor. Knowing the resistor board designation makes it easier to trace what the resistors are connected to and narrows down the suspect component(s).

 

[Garfield]

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..