Help salvaging a WD Kit6550 (or not)

[Nick]

That all looks ok, nothing obviously discolored. Again, its back to checking voltages. I guess its possible a dry joint may be the problem, so check all the soldering on the right hand channel remaking any that are questionable.

[Paul Barker]

Is this damage? What type of cap is it? Electrolytic Power supply or is it foil coupling? I cant see another though so probably power supply. Though it doesnt explain youre one channel problem it doesnt look right.

[Nick]

Its C1, 2,3 or 4 in the schematic. As already said, doesn't explain the problem with one channel. May be worth checking the value of the balancing resistors R1,2,3 and 4.

[simon]

Bienvenue JM.

This is a slightly different version to Dave's that I looked at last year. But yes, the electrolytic caps will be at least 23 years old so it's sensible to replace them all rather than just some. Dave's C1-C4 were okay but these clearly aren't. The amp was a bit of a pig to work on so if it was me I think that while I had the sub-boards out I'd replace all the lytics, not just C1-C4.

But the voltages need checking to understand what's going on. If you do measure voltages yourself and aren't comfortable doing this keep one arm behind your back! Don't go into the amp with both arms - you don't want a shock going across your heart. Use a clip lead to attach the DMM negative probe to earth, then carefully probe around different nodes with the positive probe.

[Mike H]

That all looks ok, nothing obviously discolored. Again, its back to checking voltages. I guess its possible a dry joint may be the problem, so check all the soldering on the right hand channel remaking any that are questionable.

Did also occur to me to look for 'dry' solder joints on the tag board(s), having had that kind of thing happen to me, i.e. weird intermittent noises and signal drop-outs.

[jmc]

Bienvenue JM.

This is a slightly different version to Dave's that I looked at last year. But yes, the electrolytic caps will be at least 23 years old so it's sensible to replace them all rather than just some. Dave's C1-C4 were okay but these clearly aren't. The amp was a bit of a pig to work on so if it was me I think that while I had the sub-boards out I'd replace all the lytics, not just C1-C4.

But the voltages need checking to understand what's going on. If you do measure voltages yourself and aren't comfortable doing this keep one arm behind your back! Don't go into the amp with both arms - you don't want a shock going across your heart. Use a clip lead to attach the DMM negative probe to earth, then carefully probe around different nodes with the positive probe.

Thanks Simon,
I ordered the capacitors AND some insulated gloves today...
Hopefully some fun for the WE

[jmc]

Hey guys,

as you may think, it has been a busy weekend (and a busy week )...

So:
- I swapped the faulty capacitors
- I did a first short listening test, and both channel worked
- I repeated the measures that were in the building instructions (you can see them below)
- I did a careful measure of SPL between the 2 channels (using the same loudspeaker, switching inputs) -> the good news is that I had less than 0,5db difference
- I put the amp back in my install and did listen quite a bit of music (and looked at a few movies).

The very good news:
- the crackling sound on startup and his on shutdown is completely gone
- the amp sounds very well
- I had to apply level correction in my AV receiver (that acts as a preamp here). I have a 3,5 dB correction between left and right channel but it comes from the room (I have proven that with switching channels, it is always the left loudspeaker that is a bit low, regardless it is connected to right or left channel of the amp).
- as well, I always had a light motor boating sound when I had no signal. Even that is gone.

So all things being considered, this is a success (so I nearly fainted when opening the unit).

Many thanks to you all for your suggestions and help.

[jmc]

This stated:

- I cannot explain why a fault in the PSU impacted one channel only
- I am a bit perplexed with the fact that some of the voltage are a bit or slightly below whet I measured when I initially built the unit.

Possibly, it is because I did not swap the PSU valves (5U4) and they are a bit tired?

The unit sound great anyway.

[Nick]

Good result. If there was a inbalance that has gone now, it may be something simple like a poor joint that has been fixed. The power supply caps as you say should only affect both channels. But take the win when you can. The numbers look close enough, lower voltage could well be the rectifier, or maybe a difference in line voltage between then and now.

[Andrew]

Don't they have lower line voltages in France, 220v compared to the UK's spec of 220v to 240v?

[Paul Barker]

Excellent. Hard work rewarded. Very well done.