Sony GX590 Problem!

Hi Thomas,

First of all, if you expect help, you should GIVE some help and not let people guessing.

You DO NOT have a SONY GX590 amplifier, because there isn't one!
What you have is probably a RECEIVER (Tuner/Amplifier) called STR-GX590.

To repair it you should have the Service-Manual to be able to track & follow signals. To measure you need an oscilloscope and some knowledge about how to use it and some general idea about electronic circuits.
If it were so easy everybody would do it and the 4 years I spend in training/school would be wasted.
So, it's NOT so easy.

I CAN help with the service-manual but when it comes down to how to find the problem, you're on your own.
PM me WITH YOUR E-MAIL ADDRESS for info on the manual.

mfg,

/tri-comp

Hallo,

hast Du denn schon mal die Endtransistoren durchgemessen? Liegt an der Endstufe eine positive und negative Spannung an?
Hast Du überhaupt ein Vielfachmeßgerät?

Grüße
On

Ja hab ich gemessen. Es liegen positive und negative Spannungen an. An den 2 großen NPN +40 Volt und an den zwei großen PNP -40 Volt.
Mit Multimeter, Oszilloskop und Funktionsgenerator bin ich ausgestattet.

Auf dem Kühlblech sind auch noch 2 kleinere NPN Transistoren, an denen aber nur eine geringe Spannung von unter 2 Volt liegt. Das hat mich ein bisschen verwundert, weil bei unter 2 Volt große Ströme fließen müssten, damit das Teil ein Kühlblech braucht.

Grüße, Thomas

Hi Thomas,

Oj, oj, You still have a lot to learn

Anyway, the 2 small NPN-transistors Q711/Q761 are transistors for controlling the Bias-current of the output-transistors. They are mounted on the heatsink to measure the heat generated by the output transistors.
When the output transistors heat-up, Q711/Q761 conduct more current and thereby lower the Bias. Lower Bias = less heat generated and in that way thermal run-away is prevented and the output-stage stabilized.

Hope that explains what they are doing on the heat-sink

mfg,

/tri-comp

Actually I took another look at the schematic and noticed something.
This receiver is made with an electronic source-switch.
The signal to the output-amplifier is selected NOT with a regular mechanical switch but with an IC.
Especially THIS Sanyo IC (LC-7822 / IC201) is very well known to become defective. If it really is dead you will experience exactly what you describe: Very low volume

Use your oscilloscope to check the signal-level at the input & output pins and see if I'm right.
Good luck,

mfg,

/tri-comp

ist vieleicht nur die Tape2/Monitor Funktion aktiviert (LED)?
Dann kommts auch nur ganz leise (Übersprechen)

audioB schrieb:

ist vieleicht nur die Tape2/Monitor Funktion aktiviert (LED)? Dann kommts auch nur ganz leise (Übersprechen)

...could that be why he left the forum or has no comment
It also happened to me a couple of times in the past

mfg,

/tri-comp