Sony GX 70 ES

Hi Klaus,

First of all: Your Sony is a STR-GX70ES.

It's impossible to say exactly why it cuts-out after a few minutes.
Most likely because the protection-circuit is doing it's job and something is not working as it should. It can be the output amplifier, it can be the power-supply or even the protection-circuit itself.
In your output amplifier there is a chip STK-3102/3. I would check solderings around it and do some measuring as well. For that you will need the service-manual. ...and some experience with an oscilloscope & a digital multimeter.
I can help with the manual. PM me with your e-mail address for a free pdf-copy.

Kind regards,

/tri-comp

Hello, looking on the internet to find a possible solution for my problem with my Sony STR-GX70ES, ran in to this topic.
The problem discribed looks very simular to my problem.
My STR-GX70ES started with the same problems listed above, but now the protection circuit falls in as soon as it is switched on (red "P" blinking on display).
I was also thinking about a faulty amplifier chip, in my case it's a STK3082 III, but that's a simular chip as the STK3102/3 i found out.
Can anyone confirm that a faulty amplifier chip can cause the protection circuit to fall in.
@tri-comp, i am also interested to receive a copy of the service manual.

Regards, Geert Keizer

STR-GX70ES_user schrieb:

Can anyone confirm that a faulty amplifier chip can cause the protection circuit to fall in.

It absolutely can. If one of the output transistors shorts out, for example, you'd get DC on the output and the protection circuitry activates.
For basic diagnosis, I would get a datasheet for the STK plus a multimeter and test for conductivity where it shouldn't be. A short between collector and emitter of a transistor would be a dead giveaway.

audiophilanthrop schrieb:

STR-GX70ES_user schrieb: Can anyone confirm that a faulty amplifier chip can cause the protection circuit to fall in. It absolutely can. If one of the output transistors shorts out, for example, you'd get DC on the output and the protection circuitry activates. For basic diagnosis, I would get a datasheet for the STK plus a multimeter and test for conductivity where it shouldn't be. A short between collector and emitter of a transistor would be a dead giveaway.

I already did some basic measurement on the chip.
I have measured potential on te ouputchannels to check if an undesired DC potential exsits, this was not the case.
Now i realize this could be the case because of an activated protection circuit, but the te supply voltages are still present.
I will try to measure conductivity as discribed above, but do i have to de-solder the chip to do this measurement.

STR-GX70ES_user schrieb:

I have measured potential on te ouputchannels to check if an undesired DC potential exsits, this was not the case.

So far, so good.

Now i realize this could be the case because of an activated protection circuit, but the te supply voltages are still present.

Wait.. you measured behind the loudspeaker relay? In case of working protection circuitry, there'll never be any significant DC levels at this point.

I will try to measure conductivity as discribed above, but do i have to de-solder the chip to do this measurement.

No, normally desoldering should not be required for such a basic check.

audiophilanthrop schrieb:

STR-GX70ES_user schrieb: I have measured potential on te ouputchannels to check if an undesired DC potential exsits, this was not the case. So far, so good. Now i realize this could be the case because of an activated protection circuit, but the te supply voltages are still present. Wait.. you measured behind the loudspeaker relay? In case of working protection circuitry, there'll never be any significant DC levels at this point. I will try to measure conductivity as discribed above, but do i have to de-solder the chip to do this measurement. No, normally desoldering should not be required for such a basic check.

I measured directly at the pins of the STK3082.

So the problem apparently lies elsewhere. I would guess that the STK is only a pre-driver of sorts (common for higher-end mass-market amps at the time), so there could still be something wrong after it. There should be some test points for idle current and DC offset adjustment, I'd try measuring there. If that still doesn't turn up any DC, the protection circuitry needs a closer look. Service docs would be required at this point.

Problem is still not solved
Can someone send me a servicemanual of the STR-GX70 ES?

Hi, my name is Jo,
I recently bought a second hand STR-GX70 ES.
It seemed to work ok in the shop, but when i got it home and plugged my speakers in to it there is this feedback noise like the earthing wires are loose or something.
I'm not that great technically and would really appreciate some advice.
I have tried different speakers with it, in the A and B speaker sockets, but the buzzing noise is always there. I noticed that buzzing noise changed frequency when i switched it to CD, Radio, Phono etc...
I know this is not normal obviosly i thought it might be a common problem or an easy one to fix...?
Help please,
Thanks