Recap it and get it over with especially C16
Done, fully recapped. R41 and Rbonus were replaced with 8k resistors, all I had underhand was 8 or 20k...
Perfect
Measure V across R38 in the OFF position.
V = 0V
Good. Hopefully you switched to the Millivolt scale
With no signal. Short C16 and measure V across R41
V = 0V, in both ON and OFF positions. interestingly, the LED did not turn green when switched to ON, with C16 shorted...
Can't. Only happens when C16 gets charged above D5's voltage
Check delay to LED change from OFF to ON.
Hard to estimate, I'd say 0.5-1 sec.
Better number - don't you think?
Move switch to AUTO.
Apply music. Check delay to LED change.
I'd say a good couple of seconds here, longer than OFF-ON change.
Lot's of reasons for a slight change. I thnk it's a better delay than stock?
R43 and the internal leakage current of C16 allows the timing circuit to discharge when the mains are cut. At 5RC, the cap is about 99% discharged. I can fix that with a J174 FET and a resistor. The resistor across the cut must be used too.
I'm just confused as to why ON wouldn't show a green LED with C16 shorted?! Expected?
Totally. If C16 can't charge, then delay will be infinate.
That ought to keep you busy for a while.
I'm off to Paris on sat, south of france on wednesday, spain on Friday.... Then I have a few days of work, and I'm off to Italy for a few days... Next few weeks will be a bit more on and off so I'm trying to speed things up, or at least stop somewhere reasonable! Can't complain about holidays though...
Luck you. Hiding from the big wedding?
Would you happen to have another amp lying around? If you did then I would input a signal on Low level in or Speaker in and see if there is hum present on Line out.
Check for the presence of any AC between SG of the connector and ground (No signal applied). If you have a frequency counter mode, check for the abcense of 2x the main frequency.
Let's do something a little bit different than before.
Remove Q8, Q9, Q10 and Q11
Put a 1K or so resistor between where E and C go on Q8 and Q9. Estimate the current as 80/((2 * R)+220) to size the resistors.
Tell me what you currently have installed for R13 and R14
Look at voltage between EC of Q7
Look at voltage between junction of R15/R11 and base of Q7
Look at voltage between junction of R16/R12 and the base of Q7
Consider installing the bias pot modification.
Remember as R14 gets bigger the higher voltage is applied between the B and E of Q7. The resistance should be highest in the CW position of the bias potentiometer.