Pioneer SA7800 Transistors Shorting of one side channel with two resistors burn out

[Shoaib17]

Dear Sir
A few Months Before I imported Stereo Amplifier Pioneer SA7800, When I Started Using It, Its Suddenly Got Burn Something Inside and Stop Working, While I Open It to TroubleShoot I found two Transistor Got Short and two resistors got Burn Out,
I Replaced Two Resistors and Powered them on Again until they Burn Out, Then Replace Alternative Transistors as Actual Nos are Hard to Find, and Again Replaced two Resistors.
Power it On Again and Shorting and Burning got Repeated.
Please Help me Out to Find out the Reason for Shorting Transistors.
Availability of These two Transistors 2SA1075 and 2SC2525 and Along With Which Other Parts Need to be Replaced.
Please Help me Out Guys, I Love the Vintage Amplifiers and Gears,

Thanks

 

[petehall347]

what did you replace the outputs with ?

 

[Shoaib17]

I replaced it with 2SA1076 and 2SC2526

 

[petehall347]

where did you get them from ?
what id numbers are the burned resistors ?

 

[Shoaib17]

I get those used ones, and resistors details I forgotten, it’s there in attach photos,
Thanks

 

[markthefixer]

he burned up the 150 ohm 1/2 watt emitter resistors for the drivers, in a NSA amp. R58 & R60....

it is serious.

 

[Shoaib17]

Yes, Mark
Thanks

 

[petehall347]

he burned up the 150 ohm 1/2 watt emitter resistors for the drivers, in a NSA amp. R58 & R60....

it is serious.

i suspected those would be it .. plenty of testing ahead and new parts needed .

 

[Shoaib17]

Hi
What should I do next. Please Help

 

[petehall347]

test everything . transistors diodes capacitors resistors

 

[markthefixer]

Hi
What should I do next. Please Help

get a computerized transistor tester, even a cheap $30 chineseium or (better) a Peak atlas DCA55.

learn how to navigate and identify component locations using the service manual.

get good at desoldering and resoldering components.

learn how to "drive" a dmm - for voltage (unit powered up) readings and for ohmmeter(unit powered DOWN!!!) readings
learn how the transistor tester reports good parts.

This is a NSA amp, a complex & unforgiving circuit. 100% test (out of circuit) every transistor and diode in the amp.
Look for burned resistors, but test EVERY resistor with one leg lifted out of the circuit.
Report back the parts numbers of each damaged component.
We (well, I probably) will figure out replacements.

SOME of the transistors (and especially the ones burning up the resistor) are hard to find replacements for.
The drivers are hard to find, they need to be 100 to 200 Megahertz parts..
you can use 4 megahertz parts, but distortion will be 0.03% instead of 0.003% (don't ask me how i know)

This will have to be repeated (100% testing) upon EVERY unsuccessful powering up of the unit
- you will find newly damaged by the test components.
So we endeavor to cover it ALL before applying power.... (to speed things up)

This is NOT a dig at a noobie, all (but the super experienced) do this.