Phonoland

Bit of an odd problem here. My 442 starts every track very quietly, and gradually it comes up to full volume. I understand this is more or less what AVC does, except it never used to start so quiet, or take so long to get up to full volume! We're talking up to 1 minute for volume to be normal

I recently finished my recap by replacing the 4 capacitors on the pickup input board, but didn't notice this till several days after.

I have also had the tonearm off yesterday, but the set down position seems the same. I guess set down can affect AVC but doubt it would cause this? The service manual mentions gain adjustments but doesn't sound like this would help.

With AVC off (in test mode) the amp works fine

Looking at the schematic, I suggest two areas to check:

Check the value of C23 (AGC time constant) it is listed as 100mfd. A larger value will cause longer recovery from squelch or compression.

Remove the mute-squelch relay. this should help rule out any issue with squelch voltage not being removed at set-down.

Set-dowm position has only a tangential effect on AGC in that if the stylus sets into the playing grooves apparent squelch recovery will seem longer -but not as long as you've indicated.

Does gain reduction track the same in both channels?

Rob

Rob, thanks as ever for your advice, sounds like some good stuff to be going on. I was considering the mute relay, but hadnt considered that cap. I recapped the preamp board a few months back, and no issues till now, I wonder if I have a bad cap or perhaps a bad resistor that has taken it out.

Too tired to try today but will investigate further tomorrow. I didnt meter the outputs, but the gain seems the same on both channels

If the machine worked properly till just recently, I'd check the mute relay's squelch contacts. In this case, remove the relay. . Also, it is helpful to measure the voltage on the time constant (C23) and see how it tracks. Compare the squelched voltage against that on the schematic (the online one isn't clear enough to read).

A "loud" record should produce a lot more voltage than a low record. The voltage into the photocell exciter lamp should vary in-step with the time constant cap (though it will be different).

Rob

Ok, took out the mute relay and cleaned the contacts, there's was the usual black stuff coming off with the deoxit and piece of card, but that didn't solve it.

C23 is rated 100uf and tested at 95uf on my meter. I then looked at the leads connected to the preamp board, and I THINK I may have reconnected two the wrong way around when I last had the board out. Odd as I always photograph the boards before unplugging this stuff... Anyway I reconnected it all and tested, AVC now works a charm. Guess this is down to engineer error

Feeling suitably stupid now!

Cables connected the wrong way -

E - tan - squelch
F - white green - photo cell lamp

E was in F and vice versa!