Sony TA-V33 amplifier repair

[Swarm dude]

Hello
I bought a Sony TA-V33 amplifier at a local flea market and when I turned it on - no sound came out of the speakers!
This is what I know and what I did:

1. The speakers are of right impedance (the amp supports from 4-16 ohms, the speakers are 6.8 ohms)
2. All fuses are O.K.
3. No ICs appear to be charred or burnt
4. The power amp IC has a supply voltage that is within it's limits: 72V
5. I measured voltages between the power amp IC's (STK4151II) output pins and the negative speaker terminal. Voltage reading between the 10th pin and the - terminal was 36V DC and between the 13th and - terminal was 10 mV DC.

So, it appears to me that the IC is bad?

Do I have to just replace it or do you guys suspect there could be some other fault?
Please help.
Thanks

[vtech]

Not familiar with the specific model but looks like the amp is in protection mode. Based on your readings, the IC is definitely defective. The output pins(10,13) should be in the millivolt range or it will cause the protection to kick in(not shown in the diagram). You can see how it would destroy any speaker if there was no protection.

--also make sure your plus/minus 42volt Vcc's are not missing.

[Swarm dude]

The Vcc is +/- 36V DC which gives me a reading of 72V on the multimeter. Am I correct or not?

[vtech]

While that is an acceptable number to read, you always want to measure your DC in reference to a common ground point(chasis ground--same as neg speaker in this case) rather than hooking the meter from positive to negative rails which will always equal to total rail voltage (32+32 or about74)

Main purpose is to make sure that the IC is seeing a balanced rail voltage. In most STK's it does not have to be exact and can be off by few numbers either way.

[Swarm dude]

[Swarm dude]

...so can i go forth and replace the STK, or will the new one probably die too because of some other fault that caused this one to fail?
The new IC costs around 30$ in Croatia and since I'll be spending my pocket-money on it I don't want to lose 30 bucks in a couple of seconds after I turn on the amp (if you know what I mean).
I know you can't be 100% sure unless you have this amp in front of you, I just need a green light who knows more about amps than I do.

[vtech]

Majority of STK failures are internal or due to overloading. As long as you don't get a hold of counterfeit IC, you should be OK. Don't know about your market but there are good many reject STK's are floating around that will last for a short time. As long as you deal with a reputable supplier, you should be alright.