Odd issue

[rgccarter]

Another post from me..

Been enjoying the WD88 very much - not made any mods yet apart from HT supply caps C12-13.

Noticed a strange thing yesterday however. When powering down with an audio signal the left channel turns off straight away. However, the right speaker fades out slowly over several seconds - which I would expect as normal behaviour whilst capacitors discharge?


1st Q - Am I right in expecting one channel turning 'off' immediately isn't expected behaviour?

I have had the bonnet up testing voltages, wiring, continuity etc, and nothing seems to be a miss. Also swapped around valves and temporarily swapped out some of the larger vaue caps (C7, C8 & C9) on the driver and output boards for similar values , but still the same behaviour.

Can't say whether this happened before I swapped out C12/C13 or not.

2nd Q - any pointers of what could be the cuplrit?

Not sure if it's actually affecting the sound, although I'm now telling myself the right channel sounds slightly louder and bass slightly more fuller

[Richard]

Hi, Both channels should display the same behaviour as they are from a common PSU.

Can we clarify which amp you have? Is it WD88VA? Is it a power amp only or is it an integrated with switched relay input?

I’d investigate the inputs if it has relays. Thoughts are a relay may be staying connected when powered off. Try using a different pair of input phonos.

[rgccarter]

it's a Single Input intregrated WD88VA without switched relay input

[bob orbell]

I suspect that you have a whisker of solder or wire that is shorting, but not enough to completely stop the amp. from working, I just tried my WA88 and with music playing both channels diminish equally at about 8 seconds. Do you have any discharge resistors fitted anywhere ? or even a by-pass capacitor that may be the culprit, check both channels for equal resistance, a bit time consuming, but might show something. Bob

[Richard]

The HT is bled by the divider at R25/R26 but that would affect both channels equally.
If you've not changed them I'd replace the 100uF 500V C9 caps as there is one per channel. Other than that check for a fault in construction or a wrong component value by comparing both channels as Bob says.

[rgccarter]

OK, done some poking around with a multimeter and found a few rogue resitances, some of these maybe within tolerance?
N.B. They have the right colour codes but measure differently.



I think R4B reading at 2.3M rather than 470k is probably problematic

Anything else on there jumpout as an issue?