Advice in Yamaha PC2002

[artcarmo]

Hi,im in trouble with one chanel of this amp,when i get this amp the B channel has repared, i use it for a while and the B chan burn (litteraly with sparks fog etc etc),so i fix it with motorola MJ15022/23 for the output replace bad R's drivers etc and it go good in bias& offset ,again go on fire after two hours ,but this time under" ligth load" (listen in livingroom),i realize that the MJ's are fake,again replace everyting bad but this time whit ON SEMI's parts direct from they, everyting ok bias etc and...again on fire....after few hours low volume etc etc.i got new parts and i m ready to go again but i m looking for advice (or a good fire stinguisher).so please if any can help....

[artcarmo]

The good ones that burn in the second round

[lineup]

may be some oscillation
= unstability, which in the end will corrupt the output and overload it
This can have several reasons.

- The input filter capacitance can not stop RadioWaves from enter amp
- The compensation capacitance is too low (small caps to reduce HF gain)
- The Zobel output filter is not working. 1 cap + resistor across output.


One question:
When you turned on the amp, after changing Transistors,
how hot was the heatsink, close to Output Transistors?
Without any signal at input.

[artcarmo]

i try put the schem but is like 560K ,and office doc format

[artcarmo]

cool like the other ch sink...(advice don't touch the to3 pnp and npn at same time....)

[artcarmo]

can i check those whitout the outputs in place? the oscil?( by the way i have an oscilloscope again, that dont have last two times that repare it) advice on those checks...