Fender conductive eyelet board

[fuzzman72]

Hello!

I've restored a Bassman ab165 from 1967 replacing all the electrolytic of course.
At the first test the amp sound too much hissy to my hears and the pots (on both channels) a little bit scratchy.
To cut a long story short I've found that the board has various DC voltages on it with different values from point to point, from a minimum of 1V to a maximum of 5V on an empty eyelet.

I've swapped the old board with a new one bought from moddjobs, but the results are the same.
Cleaning the surrounds of the eyelets with alcohol worsen the problem; after the cleaning the empty eyelet has now 12V DC on it.
Lifting the upper board from the bottom one has no effect.
Any suggestion?

[Jon Snell]

The eyelet is empty so not a problem.
I have been servicing older amplifiers for many years and have only found the need to replace one board and that was because of electrolyte spilliage from a leaking capacitor due to age.
Never had a problem with leaking boards if they are dry and not damp.

[fuzzman72]

Yes, the empty eyelet is not a problem at all, but now I've lifted the low voltage side of the tone stack caps and I have 11v on the empty eyelet of the treble cap, 5v on the middle cap eyelet and 2.8V for the bass cap.
This is a serious problem.

[Jon Snell]

"I've swapped the old board with a new one bought from moddjobs, but the results are the same.
Cleaning the surrounds of the eyelets with alcohol worsen the problem; after the cleaning the empty eyelet has now 12V DC on it.
Lifting the upper board from the bottom one has no effect."

Not a lot else you can do if you are convinced the board is at fault.

[mozz]

Check all your grounds, tighten the pots, transformers.

[Greg_L]

Hello!

I've restored a Bassman ab165 from 1967 replacing all the electrolytic of course.
At the first test the amp sound too much hissy to my hears and the pots (on both channels) a little bit scratchy.
To cut a long story short I've found that the board has various DC voltages on it with different values from point to point, from a minimum of 1V to a maximum of 5V on an empty eyelet.

I've swapped the old board with a new one bought from moddjobs, but the results are the same.
Cleaning the surrounds of the eyelets with alcohol worsen the problem; after the cleaning the empty eyelet has now 12V DC on it.
Lifting the upper board from the bottom one has no effect.
Any suggestion?

Alcohol and heat. Make sure it is very dry. You can fix it, it just takes effort. Soak the board with alcohol and use a soldering iron on the eyelets to purge the crud away. Dry and repeat as necessary. Finish it off with a heat gun.

[Chuck H]

I've swapped the old board with a new one bought from moddjobs,

This always surprises me. Why rebuild the circuit on the same black fiber board that has already failed? Mojo boards and other new black fiber boards are known to be semiconductive. I don't doubt that they may even be more prone to the problem with age than the old original boards because they are being sold for appearance (lots of carbon pigment used) rather than function. Black fiber boards should be avoided in my opinion.

Cleaning the surrounds of the eyelets with alcohol worsen the problem

Does this worsening continue once the solvent fully evaporates? Wetting a black fiber board with anything will increase conductivity. But it should return to wherever it started once it's dry again.

[Tom Phillips]

It would be interesting to measure for residual voltage at various points of a black fiber board in a Fender amp that has been restored and is operating properly. Also know that you can probe at any point on the board. There is no need to limit yourself to probing only at an empty eyelet.

As I work on an old Fender parts board, I always clean the old and new flux residue off the board as I work. On a full restoration, I often end up cleaning the whole board. After 50+ years of working on Fender amps, I have never needed to replace an eyelet board here in the low humidity West USA.

In the amps I have built myself, I never use black fiber boards. Although they can be made to work, I believe that the labor effort is so great that it's worth using higher quality materials. There are no bean counters watching over me in my shop.