Treble Pot Not Working on YBA1a

[KJS]

Treble pot does nothing on my YBA1a. Sounds like it's all the way off.

I am not a smart man.

What do i want to look for?

[Enzo]

Maybe the control is open electrically, or the connection to the board or the rest of the circuit has broken.

[Leo_Gnardo]

Seen plenty of bad PEC pots in these old Traynors. You can check its operation with an ohmmeter.

On rare occasions the treble cap goes open-circuit. Aside from a busted wire not much else can go wrong.

[Mick Bailey]

Firstly, make sure the pot shaft is actually moving. Sometimes they seize and the knob just rotates. Take off the knob and check it will move.

If this is OK then check the solder joints on the back of the pot. It's most likely that there's a problem with the connection where the 270pf treble feed cap attaches - it's a small ceramic disc on the circuit board. A wire could have come off, or there's a bad solder joint. If you think the cap has gone open, tack a replacement in parallel - anything near enough will do to test.

Another possibility is that the pot lug has come loose where it's crimped to make contact with the track. They can be squeezed up with pliers to get you by.

If you haven't worked on a tube amp before you need to familiarize yourself with the hazards and safe working practice.

[KJS]

Enzo, Leo, and Mick,

Thank you so much for your replies. Hopefully, I'll have a chance to take a look at it sometime today.

I have had experience with some minor repairs in an old tube amp and will be sure not to get myself killed.

[KJS]

Found it. Thanks again!

[Fragger]

Yes, I see the broken wire on/off the disc capacitor closest to the center of the picture.