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Old 22nd Nov 2022, 4:08 pm   #22
waynej4
Triode
 
Join Date: Nov 2022
Location: Chatham, Kent, UK.
Posts: 16
Default Re: Quad II problem - Rectifier blowing (GZ32)

Quote:
Originally Posted by GrimJosef View Post
Point T should be connected to ground via the transformer's speaker secondary winding - PQSRT. The cathode winding UVW should be connected to ground via the 180R cathode resistor. Since UVW should be electrically continuous I'm surprised that the good amp only shows T connected to V. It might be worth repeating the measurements from T to U and V. It can be hard to push the point of the meter test-lead through the decades-old insulating oxidation layer on a transformer terminal, resulting in an apparent open circuit when in fact there is continuity.

Cheers,

GJ
T does indeed connect to ground. I've measured T, U, V, W again and you are correct, they are connected. Both amps show the same measurements across these terminals.

Also X, Y and Z are connected on both amps ( I previously thought X and Y weren't). Only difference I see on them is the resistance is higher on the bad amp between X and Y, 300ohms compared to 120ohms on the "good" amp.

Quote:
Originally Posted by Diabolical Artificer View Post
Next, you need to find the short and any other potential faults. With the amp powered off, meter set to ohms, black lead to chassis or ground take a reading at the Y terminal on the OPT, this is with the GZ32 unplugged. You should get a reading of a few hundred kilo ohms or more, if it's a few ohms you have a short. Repeat with a reading on the other big cap C4, in your case it's replacement.

Andy.
For the "Bad" amp, I get a reading of 250ohms from the Y terminal. For the "good" amp it is around 6Mohms. Same for the C4 Cap.

Quote:
Originally Posted by cathoderay57 View Post
You're right of course; time that I re-engaged my remaining Braincell ..... We still don't know if the 32+32uF caps had enough headroom on their peak voltage rating though! Jerry
The C4/C6 cap is rated at 500V.

Thanks again for the suggestions/help. It is very much appreciated.
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