Help trouble-shooting a preamp

[The Zen Master]

The short story is:

I purchased a Mojotone "Music Man Clone" 2-band bass preamp (3-knob version) and installed it in a kit bass (no longer available - I got to hand select a neck) with a Seymour Duncan 70's Music Man Alnico 5 4-string pickup, a Fender American Standard Bass Bridge (through body) and Schaller tuners (I sent the neck out and had it professionally re-fretted and leveled).

It sounded so good I could not believe my luck. A few professional friends played it and were equally impressed.

One day, 16-months later (4-months after Mojo warranty expired), I picked the bass up, plugged it in, and the treble control was having no effect whatsoever. The bass did nothing but sit in a closet since the last time I played it.

I sent it to Mojo and they were kind enough to replace everything. I reinstalled and the bass sounded beautiful.

Then one day, bam, I pick it up and plug it in and no treble control whatsoever.

I am just a guy that played the bass when I was a kid and I owned a 78 Stingray - that I wish I still had. I know nothing about designing circuits but I soldered a few heathkit radios together when I was a kid.

If I wanted to test the treble pot (1M Rev Log) itself, to make sure it is functioning as expected, how would I do that? What tester do I need and what is the procedure?

I would really like to figure out what went wrong with this preamp - twice.

If anyone can help I will be forever grateful!

 

[Crater]

If I wanted to test the treble pot (1M Rev Log) itself, to make sure it is functioning as expected, how would I do that? What tester do I need and what is the procedure?

Resistors are tested with multimeter set to measure Ohms (resistance). To get an accurate reading, you should probably disconnect the pot from the preamp; there could be components in parallel with the pot that could throw off the reading. (I did not make this video)

 

[The Zen Master]

Thanks Crater I will check it out.

 

[The Zen Master]

I haven't done anything yet but I did send an email to Mojo - they suggested I inspect everything to see if maybe anything bent over time and is shorting. It was snug going together but I did not feel any resistance or pressure but I will give a look.

However - change in plans - I am going to build one of these: MM Stingray 2 band shared PCB design - a copy of a pre EB Stingray preamp from another thread here on Talkbass (ordered parts for 3 preamps).

My kit stingray bass came with 2-pickups - I only installed one Seymour Duncan pickup in the rear position, put the battery in the pocket for the forward pickup, and used a single pickup pick guard. There is ample room for the battery and the preamp in the forward pickup pocket and this will eliminate any possible crushing or bending of anything. I never liked that mojo double-sided-tape'd the preamp to the back of the pots in the first place.

Once I get the new preamp working I will swap everything and troubleshoot the mojo preamp later.

Should be an adventure!