In case it is relevant, I am using as my GND point the external GND terminal on the rear of the AM, next to the Phono inputs, which makee it easier for me to hold the GND probe steady whilst I measure with the DMM Input probe

Apologies for my miss-spellings !

 

While I was taking power rail measurements, I noticed a brown area near to Q315 and I uploaded some photos. It is difficult to work out if this is just old, darkened resin or if it indicates perhaps scorching near Q315 ?

 

While I was taking power rail measurements, I noticed a brown area near to Q315 and I uploaded some photos. It is difficult to work out if this is just old, darkened resin or if it indicates perhaps scorching near Q315 ?

 

Strange voltage readings.

Can you take a photo of your multimeter showing the entire meter with the screen and range setting while you are taking a reading from the positive supply voltage?

Using the GND on the back of the amp is ok for now until we can figure out why your reading is 40V and not 55V.

 

Sorry for the delay in following up my measurements, I have taken readings this morning and attach photos also. The reading today is +38.76V. Should I measure at other points to investigate why the rail is below 53V ? Thank you !

 

I have been googling reasons why a power rail should reduce from 55V to 40V but not found any clues. However, given the possible scorch marks near Q315 I wonder if a damaged Q315 might somehow drag down the power rails ?

 

Start at the Transformer and measure the AC, then go to the bridge rectifier and measure the DC , if the AC is wrong could be transformer, if not then the DC supplies to each channel needs to be isolated to see which one is pulling it down.

 

Thank you Dodgydave, I will take the measurements and report back.

 

I cannot see pulling the supply voltages down by that amount without generating heat and smoke somewhere on the amp.
I would suggest touch, feel, smell for hot components. Be careful when touching.

You can also try to find a thermal camera which will instantly reveal your hot spots. Some smart phones can do IR imaging.

We know that the right channel is out of whack. I would be inclined to search for what is causing this and maybe the supply voltages might return to normal.

 

I cannot see pulling the supply voltages down by that amount without generating heat and smoke somewhere on the amp.
I would suggest touch, feel, smell for hot components. Be careful when touching.

You can also try to find a thermal camera which will instantly reveal your hot spots. Some smart phones can do IR imaging.

We know that the right channel is out of whack. I would be inclined to search for what is causing this and maybe the supply voltages might return to normal.

Thank you also Mr Chips. I couldn’t get to my amp today but I will do tomorrow and check out the voltages and temperature. The only signs I have seen so far of potential damage is the staining near to Q315 as posted on the photos I uploaded.