05-11-2015, 09:51 PM
The service manual is attached...
The voltages seen at the loudspeakers look normal to me - it's a bridged circuit running from 15V. The output amplifiers are TDA7384, which are pretty generic chips used in car audio, etc, so should be easy enough to source if needed. In fact, quite a lot of the silicon is non-Sony, which is good news.
Have you checked all the power supply rails?
Next, have you checked the operation of the muting circuitry?
Have you tried with a digital source (just need to hook up a DVD player)?
In-between the stereo analogue input and the audio amps is a bucket-load of complicated stuff. The audio is converted to digital and passed through DSP (IC802) which presumably does a Dolby Pro-Logic decode, or perhaps one of Sony's own "make surround from stereo" algorithms. There are also digital inputs - S/P-DIF or TOS-LINK, which will be carrying 5.1 Dolby Digital or DTS, which the DSP is able to decode. Finally, there's a USB input, which is basically the playback side of a USB sound card on a single chip, generating analogue audio that gets converted straight back to digital using the same processing as the basic stereo input.
Who was it that said "Big chips don't fail"? Let's hope he was right
All you can do is get the 'scope out and start analysing. Follow the audio through to the codec chip IC804. If analogue audio is making it to pins 29 and 30 (Left) and 31 and 32 (Right), that's good...
Next, does audio emerge on pins 23 (Centre), 24 (Sub), 25 (Rear L), 26 Rear R), 27 (L), 28 ®? If there's anything on any of those, that's good because it puts the problem somewhere between the codec and the audio output stages.
After that, there are some buffers and a volume control chip. All good analogue stuff that can be 'scoped. That's followed by some EF buffers, a LPF made from op-amps, more muting transistors, and the power amp ICs. Lots of complexity on the muting control side, as always.
The trouble is, understanding the schematics will take some time. Troubleshooting is not exactly easy with this sort of stuff - lots of surface-mount to contend with. And if it's one of the big chips, then you might be stuffed (if you can source them, can you change them?). From a quick Google, it appears that they are not the most reliable product in the world. For me, it's one of those quick "I'll check it's nothing daft", because anything more elaborate won't be economical... These are up to 12 years old now - that's not a bad lifespan for a modern bit of gear. Let's hope it's something age-related like dry joints or bad capacitors... At least it pre-dates lead-free solder.
Good luck,
Mark
The voltages seen at the loudspeakers look normal to me - it's a bridged circuit running from 15V. The output amplifiers are TDA7384, which are pretty generic chips used in car audio, etc, so should be easy enough to source if needed. In fact, quite a lot of the silicon is non-Sony, which is good news.
Have you checked all the power supply rails?
Next, have you checked the operation of the muting circuitry?
Have you tried with a digital source (just need to hook up a DVD player)?
In-between the stereo analogue input and the audio amps is a bucket-load of complicated stuff. The audio is converted to digital and passed through DSP (IC802) which presumably does a Dolby Pro-Logic decode, or perhaps one of Sony's own "make surround from stereo" algorithms. There are also digital inputs - S/P-DIF or TOS-LINK, which will be carrying 5.1 Dolby Digital or DTS, which the DSP is able to decode. Finally, there's a USB input, which is basically the playback side of a USB sound card on a single chip, generating analogue audio that gets converted straight back to digital using the same processing as the basic stereo input.
Who was it that said "Big chips don't fail"? Let's hope he was right
All you can do is get the 'scope out and start analysing. Follow the audio through to the codec chip IC804. If analogue audio is making it to pins 29 and 30 (Left) and 31 and 32 (Right), that's good...
Next, does audio emerge on pins 23 (Centre), 24 (Sub), 25 (Rear L), 26 Rear R), 27 (L), 28 ®? If there's anything on any of those, that's good because it puts the problem somewhere between the codec and the audio output stages.
After that, there are some buffers and a volume control chip. All good analogue stuff that can be 'scoped. That's followed by some EF buffers, a LPF made from op-amps, more muting transistors, and the power amp ICs. Lots of complexity on the muting control side, as always.
The trouble is, understanding the schematics will take some time. Troubleshooting is not exactly easy with this sort of stuff - lots of surface-mount to contend with. And if it's one of the big chips, then you might be stuffed (if you can source them, can you change them?). From a quick Google, it appears that they are not the most reliable product in the world. For me, it's one of those quick "I'll check it's nothing daft", because anything more elaborate won't be economical... These are up to 12 years old now - that's not a bad lifespan for a modern bit of gear. Let's hope it's something age-related like dry joints or bad capacitors... At least it pre-dates lead-free solder.
Good luck,
Mark
