Hello wonderful people

I have to admit defeat on this one. I'm fixing a HiWatt clone amp, based ont he Ceriatone DR504 clone. It's a beautiful piece of work by the customer. The problem in very low output and lots of DC on the pots.

Working my way through the problem I found an unconnected turret which measures ~70Vdc relative to the chassis. The paxolin board is new, there is no visible short and no continuity between the turret and anything surrounding it. No DC on the board.



Checked my DMM and seems to be working fine. I'd ignore it but wondering if it might be a clue as to why there is DC elsewhere (on other disconnected turrets and the pots). You can hear the DC on the pots so I'm sure it's there!

I wodnered if it was just a poor DMM (UniT UT58C) or just a random value given the turret isn't connected and just floating at a random voltage

Peace adn love guys, would be very grateful for any insight

Pat

ps - no schematic but here is Ceriatone's layout from their website which this amp was based on:

 

What point in the circuit (and where on the chassis) are you using for the common connection of your voltmeter? Is the chassis aluminium?

 

Thanks Keith

out of habit I stick it in the fixing screw as seems fine rest of the time. It is aluminium. Have put the other lead right on the bare chassis edge as well

pat

 

Many years ago I was servicing a HP 201C Audio Oscillator. It had a small amount of distortion on the output that should not have been there. When I measured at the test points, I got some strange results, both AC and DC. After many hours of checking, I discovered that the two aluminium chassis which were bolted together had become oxidized and insulated from each other. I cleaned the contact areas with wire wool and it worked when I put it back together.
The strange DC voltage you measured reminded me of that. Could one of your chassis ground points have become insulated from the chassis? That probably still does not explain the voltage you measured on a blank turret but it may help you find the fault in the amplifier.