2230 buzz after recapping P150

[bibota]

Buzz first, are you plugging in with the thing on and the volume up a bit? It would be normal to get a buzz when the center pin of the cable hits the connector, before the ground connects. With either cable you have ground, so the next one you plug in won't buzz. Do you have buzz with both cables plugged in? That would be abnormal. In general, don't plug in with power on and/or volume off zero.

If that cap is supposed to be non-polar, you have to order the right type of cap and replace it, lest it explode or other bad things happen.

Just as you say Conrad, coming back to the buzz: I find that what happens now is well beyond the normal short "pin hits connector" kind of thing.
For you to get a true taste of it, here's a recording. Some may find it irritating so please turn down your volume a bit. The sequence of events (approx 5 sec each) is:
1. volume going from zero to 10 o'clock with no RCA plugged,
2. Red pin being inserted into Left Phono,
3. White into Right Phono,
4. White out
5. Red out

 

[bibota]

I think the cap on the back of the board is wrong too but that needs verified.

Thanks rBuckner, had it reversed but makes no difference to the noise.
With the buzz as strong as ever after all of the changes made to the caps orientation, could the main problem be elsewhere? Perhaps a bad ground, as Conrad suggests.

I had a few spikes of hope along the way, first when discovering a broken wire connection to J157, and another one to J158 the next day. Again, it made no difference to the sound after soldering. At first I thought that lack of continuity may have been the cause of the buzz but no, surely both must have happened while fiddling with the board trying to repair it.

 

[ConradH]

Gain of a properly operating phono section is extremely large. I'd expect exactly what you're hearing. BTW, in particular with phono stages, one never plugs or unplugs with the volume up or even the power on. That said, there's a certain strangeness to the sound, a wavering and lack of edge I'd normally expect, but so far you haven't described anything unexpected unless there's some other factor I'm missing or don't understand. It does go away when either cable is fully inserted?

 

[bibota]

Gain of a properly operating phono section is extremely large. I'd expect exactly what you're hearing. BTW, in particular with phono stages, one never plugs or unplugs with the volume up or even the power on. That said, there's a certain strangeness to the sound, a wavering and lack of edge I'd normally expect, but so far you haven't described anything unexpected unless there's some other factor I'm missing or don't understand. It does go away when either cable is fully inserted?

Hi Conrad,
Thanks for the plugging-unplugging phono tip.

Regarding the buzz, the most unexpected thing is that it has appeared, whereas previous to recapping P150 it wasn't there at all.
Before that, the inserting of the RCAs was a very unremarkable thing, only accompanied by the discrete pop of the pin touching connector. And the faintest of background noise after that, completely undetectable unless you really went chasing it and turned the volume close to the max with no musical signal from the record.
Also to rule that out, the turntable's ground wire is indeed hooked to the amp.
To me, this bad sound certainly signals something being wrong. Perhaps even in a different area than P150, possibly something that got disturbed while moving the thing about..

 

[bibota]

It does go away when either cable is fully inserted?

1. Before any RCA inserted: reasonably quiet but nothing like the old days (a slight hum is audible, noisier than I was used to)
2. With one RCA inserted: very loud buzz
3. With second RCA inserted: the very loud buzz goes, the hum remains

 

[ConradH]

Ok, if you get a buzz with one RCA fully inserted, there's almost certainly a ground problem. All the various grounds have to be connected together at some point. Power off, measure resistance between RCA shells, chassis, power supply common and ground points on the phono circuit board- you'll have to look at the schematic and layouts to find them. There almost has to be a broken wire or trace somewhere in the ground system.

 

[bibota]

...measure resistance between RCA shells, chassis, power supply common and ground points on the phono circuit board- you'll have to look at the schematic and layouts to find them.

Thanks Conrad, this is just the kind of practical advice I needed.
Up until now I was using a children's sort of multimeter, but I ordered a reasonably accurate one which should be delivered today by Amazon. I'll print the schematics, start measuring and see what conclusion I can come up with.