PPIMV Troubleshoot

[Dave1992]

Hey guys,

First off, sorry if a post like this has been done before but here it goes...

I've decided to install a PPIMV on my 2011 1959slp (w/fx board) following this video instruction https://www.youtube.com/watch?v=e4EXWkt01A4 .

So far everything check's out, there is no short anywhere and I read the proper resistance on the negative voltage supply.

When I check for the negative bias voltage there's -140 on pin 4 of the powertubes and nothing on pin 5. I haven't switch the amp off stand by so far to prevent damage to the tubes.

Anyone can help me figure this out? I'll try post pictures as well but the servers seems to be full... Thank you very much

[Dave1992]

By the way, it's a 250k dual gang pot with the 2.2m resistor configuration just like in the video above. Everything is the same.

[danman]

Pin 4 is the screen grid so it should not have any negative voltage on that pin. With the amp in standby, pin 4 should not show any voltage so unless you wired something wrong, your meter is probably just showing a ghost voltage. You can remove the power tubes, power up and switch the amp into play mode and you should see high voltage DC on pin 4. If pin 5 does not show a negative bias voltage in the area of -40 to -50 vdc, work your way backwards through the bias circuit to see where you are losing voltage. Check the turret on the board where the two 220k resistors use to connect to. From there work your way backwards through the bias circuit checking for proper bias voltage.

If your jumper wire that led from the 220k junction to the 15k resistor at the top of the board was run under the board, I'm guessing that it fell out of the turret when you heated the turret to remove the 220k resistors. Look under the board to see if that jumper is still connected properly. If your jumper is ran on top of the board then you can disregard this part.

[Dave1992]

EDIT: Everything works fine!

So I've taken the tubes off the amp and put it in "play mode" and Pin 5 had -38.5v on each tube socket. There is no sign of a short anywhere else. So basicaly I'm all good right? There was no voltage on pin 4 aswell.

[danman]

Excellent! Your meter was probably just reading a "ghost" voltage when the amp was in standby. You will see this phenomenon occur when measuring a point in the circuit that does not have any voltage.

[Dave1992]

Any idea why this can happen?

[danman]

This may explain it better than I could.
http://www.extech.com/blog/posts/150323 ... ng%20power.
https://www.grainger.com/know-how/safet ... t-voltages