driver testing [resolved]
- Thread starter joralieu
- Start date
Those voltages suggest that that C4S board should be working, so I'd be looking for missing jumpers or a broken wire that's not allowing the regulator to pull things down properly.
What OB voltages do you see on each side?
7V is the correct value. 15V means that you have a bunch of current being sucked down somewhere else.
On the 9 pin socket on the side with 15V, there is a little resistor that connects to the earth lug on the 5 pin terminal strip holding all the zener diodes. What is the DC resistance between the star ground screw in the center of the chassis and that terminal where that resistor connects? This connection not being 100% would prevent the 5670 regulator half from doing its job properly.
On the 9 pin socket on the side with 15V, there is a little resistor that connects to the earth lug on the 5 pin terminal strip holding all the zener diodes. What is the DC resistance between the star ground screw in the center of the chassis and that terminal where that resistor connects? This connection not being 100% would prevent the 5670 regulator half from doing its job properly.
I've never seen a 431 fail in the way you're describing. I suspect a broken wire or missing jumper on the C4S board.
There's a terminal labeled "X" on the PC board, can you measure the DC voltage on that pad on the side where you have 15V at Kreg? Also it wouldn't hurt to just swap the 5670 tubes to be extra sure this isn't something that's tube related, though that seems quite unlikely under these circumstances.
Fundamentally this may have a lot to do with the 2.49K and 249K resistor swap. You could try replacing the 431 regulator there, and that might work, but you may also just have an iffy joint or a lifted trace on one end of the 2.49K resistor on that side of the board. I would probably pop in a new regulator and add a little heat and solder to the 2.49K resistor.
Ok, I finally got the hooked up and still have a problem. The left channel is significantly lower output than the right with the trimpots turned all the way up. Would this be a problem with the driver board? I have switched tubes and cables around and the left side remains low.
Are the DC voltages consistent between channels? Most of the time when we see something like this, it's an issue with output transformer wiring if everything else is equal between channels.
You can post some build photos, concentrating on the areas around the output transformers.
