Sony FA-T55 apm problems

[cseko]

Hello everyone.
I just got my hands on a real vintage Sony FA-T55 amplifier, which is broken. When I first took it apart I noticed some melted soldering and some brown spots on the PCB around some of the transistors, I changed them, also a couple of the caps as well, just to make sure, and I actually made it turn on, the sound was horrible, so I changed the transistors from the power amp, but even before I started, it went off, and won't come back to life. It's really annoying, as I saw it working, so I know I'm not that far from the solution.
There is two relays, one for the main power, one for the speakers protection, both (?) driven by an HA12002 IC. I'm suspecting that the problem is around the relay driving circuit, but I really don't want to order a lot of parts, before I made sure it's necessary. Has anyone have some experience about same kind of stuff, or any advice or help? It would be wonderful, as it's really a fine little amp, I want to make it work anyway. Thanks a lot!!!

[anatech]

Hi cseko,
Sony FA-T55? Never heard of that model. Could it be a TA-F55 by chance?

Firstly, the HA12002 is a speaker protector type circuit. It will prevent the speaker relay from connecting speakers to an amp with problems. Learn to love that little chip. It's not likely to be your problem though. The power relay is not driven from the speaker protector normally.

Can you show us a picture of the inside? It may be one with a switching power supply, or it may have a normal transformer. If it's very light, it may very well be the switching power supply type.

Questions for you now.
1.) Where did the replacement transistors come from?
2.) Where the transistor numbers the same as the ones you took out?
3.) Did you use fresh thermal compound (not the computer type!)?
4.) Where the insulators cleaned off and in good condition (no cracks, creases or missing bits)?
5.) What do you have in the way of experience?
6.) What test equipment do you own or have direct access to?
7.) What measurements have you made so far?

-Chris

[cseko]

Oh yea, my bad it's ta f55. And the problem started before I even touched anything, so I'm pretty sure that its not the replacement parts. I have the schematics and before when it was working, I made the correct measurements, and now it's dead so all I can measure is the power supply, where it connects to the pcb, it has the correct voltage (around 300V). I have in the way of experience a few years, building stuff, I started to get addicted by audio in the last year, but I've done a lot of electronics before. And inside it have a pulse power supply, here is the picture, i have the schematics too. thanks

[cseko]