Sony HCD-SH2000 No sound

[Rusenga]

Hi techs, I have a Sony hcd-sh2000 sound system which has very faint sound output behind a loud humming noise. I have tested all semiconductors voltages against ones in the schematic and all seem to be ok except mute output from system controller IC which is a 3.3v but is appearing and disappearing. I have isolated this leg but still the 3.3v is on and off. Anyone ever come across this fault please help.

See attached the schematic and the main and amp boards.

[Jolly62]

Re: Sony HCD-SH2000 No sound

Did you check Q207? It seems to be the common component to mute all the amplifiers.

[Rusenga]

Re: Sony HCD-SH2000 No sound

Thank you for your reply. I did check Q207 it has -3v on the collector, 3.3v on the emitter and 3.2v on the base. However pin 51 on IC100 has a 3.2v out of the IC which is coming on and off every 3s or so. I isolated the pin and there is no change the 3.2v is still going on and off. With pin 51 on IC100 isolated, the voltages on Q207 are stable. I am suspecting IC100 might be faulty but I may be wrong.

[Jolly62]

Re: Sony HCD-SH2000 No sound

If IC100 was faulty, I think the system would not switch on at all.
Have you checked all the power lines?
What about pins 63, 71 and 72 on IC100?
Considering the "pulsing" of pin 51, I would check all the pin values arriving at IC100.

[R_J]

Re: Sony HCD-SH2000 No sound

I would suspect a bad audio output, either a bad ic406~409 or a bad output transistor Q1418~1425.
I would check if there was any DC voltage on any of the speaker connections, it could be that there is dc on the outputs and the protection circuit on page 41, is detecting this and telling ic100 to mute any audio.