Fender BDRI +16/-16 Supply

[Helmholtz]

Please measure pin 1 and pin 3 voltages.

[bobloblaws]

Do you think adding a cap might fix it?

Weird, now I'm seeing .065V on V1A pin 2 rather than -0.197V. Come to think of it, that's what I recorded yesterday when I was checking all the tube pin voltages. Maybe the problem is board conductivity after all.

[bobloblaws]

Please measure pin 1 and pin 3 voltages.

Pin 1 -> 234V, pin 3 -> 1.8V

[g1]

Do you think adding a cap might fix it?

I would think so, but it's kind of a band-aid solution. Easy enough to test, either at the jack if it's chassis mounted, or right in your cable or guitar itself.

[bobloblaws]

I just thought of something. When I was working on the bottom of the PCB there was a lot of damage around the first couple of pots, looked like heat damage as well, strangely. I re-soldered as well as I could and checked continuity, but I'm wondering if there is conductivity on the board as xtian was talking about above.

Here's a few snaps.

[Helmholtz]

With the given wiring, each input would need its own coupling cap to make sure there's always a DC grid leak path through R3.

[Tom Phillips]

Here's a few snaps.

Is that black crud old solder flux and just on the surface? If so, I'd give that area a good cleaning with IPA & a toothbrush. An excellent (NASA soldering course type) procedure, if you are up to it, is to remove all the existing solder, then clean the area with IPA, then re-solder and then give the area a final cleaning with IPA. you certainly do not want residual solder flux spanning the space between two contacts.

[bobloblaws]

With the given wiring, each input would need its own coupling cap to make sure there's always a DC grid leak path through R3.

I'm not sure I understand. We are still talking about trying to solve the DC on the grid problem, yes? I was thinking of putting a cap in series between the junction of R1 and R2 and R4. This would not change the grid leak provided by R3, or am I way off base?

[Helmholtz]

That will work - but only with input 2.

[bobloblaws]

That will work - but only with input 2.

Sorry Helm, I still don't know what you are driving at. How will the grid leak be affected for input 1?

[Helmholtz]

DCV will not be blocked for input 1.

[bobloblaws]

DCV will not be blocked for input 1.

Right, but I don't understand why. The 1M grid leak is still there.

My lack of basic theory is obviously showing. Here's a little diagram of what I've done. It removes the scratchy sound from turning the guitar volume up or down and the tone in general seems OK but the voltages on V1A are really messed up.

[Helmholtz]

See my post #36.
With your wiring the tube has no DC grid leak path through the grid leak resistot R3, so the grid is floating.

[bobloblaws]

See my post #36.
With your wiring the tube has no DC grid leak path through the grid leak resistot R3, so the grid is floating.

Ahhh, I think I finally figured out what you are driving at. The cap is blocking the path between the grid and grid leak resistor. And the point you made about it working only for input 2 assumed I would put the cap between R1 and the junction of R2 and R41.

Thanks for your patience!

[bobloblaws]

Is .01uF an appropriate value for this scenario?