Incorrect voltage after assembly debugging

[JosephDuffy]

Hi everyone,

I've just put together my Reduction and performed the tests. The resistance tests all passed, but the voltages failed on 2:

Terminal 10 is 74.3V when it should be 0
Terminal 60 starts at ~120V and slowly drops. I let it get to 100V in about 20 seconds. Should be 165V

I will also note that the LED connected to B4 turned off when measuring terminal 30, but came back on after turning off and back on the amp. It also turned off when measuring 51 but came back on a few seconds later.

I've done a visual inspection of the circuit and gone back through the instructions to see what I missed but I can't spot it. A bad solder somewhere maybe? I'm finding it hard to link the 2 problems, unless they're not related.

Any help would be much appreciated

[JosephDuffy]

On my third look I spotted that 33 and 34 red and black wires were swapped. I have swapped these and this fixed the reading on 60, but not 10.

With my more fresh eyes I've taken another look and can't spot the issue. I will take another look at it in a couple of hours in case the problem jumps out at me.

[Paul Birkeland]

Please post photos of your build, as the high voltage at terminal 10 is very undesirable. 

70V at terminal 10 could just be a very poorly soldered 475K resistor that isn't grounding the output end of the capacitor.

The on/off behavior of the LED's is also very indicative of soldering issues, as loose parts will cause this kind of intermittent behavior. 

-PB

[JosephDuffy]

Please post photos of your build, as the high voltage at terminal 10 is very undesirable. 

70V at terminal 10 could just be a very poorly soldered 475K resistor that isn't grounding the output end of the capacitor.

The on/off behavior of the LED's is also very indicative of soldering issues, as loose parts will cause this kind of intermittent behavior. 

-PB

Thanks for the reply. I've uploaded some photos of the build. I'll take a look at the 475K resistors and touch up any joints that look loose or poorly soldered.

[Paul Birkeland]

Yeah, resolder those joints at 10 and 11 and see if that voltage disappears.

[JosephDuffy]

Sorry for the delayed reply; I recently moved cities for a job and I've been busy!

I've re-measured the resistances and I've found that terminal 10 is giving me anywhere between 30KΩ-170KΩ. I have resoldered terminals 10 and 11 but this has not fixed the problem. I have also checked the surrounding terminals and cannot see any issues. I've uploaded a photo of that section of the board, in case that's of any use.

[Paul Birkeland]

Do you still have DC voltage greater than 0V at terminal 10?  What voltage do you see at terminal 9?

Based on your descriptions, I would frankly reheat every solder joint in this amplifier.  The fact that probing back around the power supply terminals causes issues downstream points to flaky solder joints there also.

[JosephDuffy]

Do you still have DC voltage greater than 0V at terminal 10?  What voltage do you see at terminal 9?

Based on your descriptions, I would frankly reheat every solder joint in this amplifier.  The fact that probing back around the power supply terminals causes issues downstream points to flaky solder joints there also.

I was working my way through the various joints and not seeing any improvements, so I decided to swap the 0.47µF 400V capacitors that are across 2 and 10 and 23 and 31, and I've observed that I now get a correct reading (~470KΩ) on terminal 10, but the wrong reading (~30KΩ+) on terminal 23. Does this mean that replacing the capacitor across 10 and 23 could fix the issue?