[Pete Birch]

Hi,

Firstly, apologies for my first post being a question.

I recently bought a second-hand Sony STR-DB1080 receiver and am having a problem with it - basically when the amp is first switched on everything is fine but then the sound from all speakers (5.1) starts to distort after the amp has been running a little while (how long this takes varies, anything from 10 mins to 2 hours before it starts).

This happens no matter what the source (radio, digital TV (analogue inputs) or DVD (digital coax)) but only when using the surround processing i.e. if I switch it to 'analogue direct' then the distortion immediately stops (but then you only get 2 channel sound from analogue sources).The distortion occurs no matter what surround processing is used (DD, DTS, DTS-ES, DD-EX, Sony's Digital Cinema Sound, Prologic, Prologic II etc).

I've searched this forum but haven't been able to find anything useful so thought I might see if anyone could help.

I have the receiver set up with pre-outs going to my Altec Lansing ADA995 5.1 surround system that came with my Dell PC (the sub has an amp in it which powers the speakers) All speakers are 8 ohm so I've set the impedance selector on the back of the amp to 8 ohm, although I've also tried 4 ohm, which has no effect on the problem. I've also tried wiring the speakers directly to the normal speaker-outs rather than the pre-outs, which worked fine but produced the same distortion. The distortion is even produced when headphones are connected, although as above it stops when using 'analogue direct.'

I've tried moving the system to a different room, in case there was interference from something else, but the same thing still happens.

I've tried changing pretty much all of the amp settings that seemed appropriate and have reset the amp settings and the surround field settings, but nothing helped.

Any help / suggestions would be greatly appreciated.

Cheers

[Dick Knisely]

Can you return it? Sounds very much like a heat-induced failure of a component. Lots of possibilities some simple and some not. Sounds like once the amps warm up the heat expansion makes a connect become iffy or the heat is making something go way out of spec. Neither of those is normal.

The fact that direct mode avoids the problem, I think, puts the failing component/connection in the logic section as opposed to the preamp/amp portions.

I'm guessing but if it were mine, I'd be expecting a complete failure soon.

[Steve Berger]

It does seem like a failure on the Digital Board and unfortunately there are very few simple problems that can occur there (voltage regulator IC?)

However, loosening board mounting screws can cause ground problems and re-tightening them is a simple fix.

[Pete Birch]

Thanks for the suggestion - I've tried tightening every accessible screw (none were loose) but this doesn't seem to have had any effect

Any other ideas?

[Steve Berger]

Have you tried tapping (gently) with a non-conductive stick on various things. There are many possibilities. The front panel boards pass data through many connectors back to the digital board. Relays can come unsoldered and chatter or cut in and out. STRxxx, STKxxx, and UPCxxx IC's can develop thermal problems. Solder connections often respond to vibration while thermal failures can respond to freeze sprays. Oscilloscopes are needed to signal trace but most of the connections on the digital board are not accessible to a probe.