fender princeton chorus (1988)

[mrtunes]

i have a princeton chorus - the board says 1988 on it (i got mine in the mid-90s). the likely cause of my problems below is that for many years it was stored in a basement, so i believe things are rusted inside from changes in temperature.

on input jack 1, the connection is too unreliable to be used. input jack 2 works a little better, but if you do something like sweep the treble knob, sound cuts in and out, and then gets unreliable as well. i am guessing jack 1 needs to be soldered into place a little better or replaced altogether.

i have been able to open the amp up and dropped a bit of contact cleaner into the pots (i was given a small tube by the music store, and was told only a small amount would be needed).

how can i diagnose this a little more precisely? i have a multimeter but wouldn't know where to begin with the schematic and writing down values.

[Chuck H]

The amp probably just needs more extensive cleaning inside. Get some contact cleaner/deoxidizer and work over all jacks, pin connectors, switches and anything else that isn't a soldered connection. Then do it again. Long storage can result in a lot of oxide build up.

If the problems continue and the jacks are board mounted it's possible that the trace pads on the board for the jacks are damaged or that the jack/s are indeed just worn out.

Due the amps era and age it's also possible that you have some leaky or bad capacitors. This could also cause some of your symptoms, but is less likely.

[nashvillebill]

Don't forget to clean the contacts in both the Mono and Stereo return jacks, these are switching jacks so they will cut out the signal if they are dirty. Same with the headphone jack.

I have one of these, it's a great little amp with a very clean chorus.

[g1]

Does it have the plastic jacks with the metal jack nuts? If the plastic threads are stripped and the nut no longer tight, then it is more likely you have bad solder connections from the jack wiggling around.

[Chuck H]

Does it have the plastic jacks with the metal jack nuts? If the plastic threads are stripped and the nut no longer tight, then it is more likely you have bad solder connections from the jack wiggling around.

I'm not even a repair guy and I can't count how many repairs I've done because of this. I install the jack upside down (if it fits that way) and then use short traces to the board so there's less stress on the pads (or traces I soldered to just ahead of where pads use to be). If there's no room for upside down mounting I try to get a jack with metal threads and engineer some kind of chassis isolation with non conductive washers. I can't imagine how many amps have been tossed because of that failure.

[nashvillebill]

They're all the multi-pin plastic jobs like this:

I have a reference that the generic form of this jack from www.tubesandmore.com is S-H507-A and folks claim that one holds up better than the FMIC version.