Electronic Circuits and Projects Forum

Hi all. I'm a bit of a no-nothing but due to skintness, I need to
fix my kids guitar amp which got dropped down some stairs. It
stilll works but the shafts have been broken off the pots which I
need to replace. They are circuit mounted mini pots but I have a
cunning plan to run wires from the circuit board and replace them
with standard mini pots from maplins to save money. what I need is
someone to help decipher what is marked on the pots and tell me what a
suitable replacement would be.
Below is a list of the pot stampings and their function.
1 B50K 9924 Q volume
2 15A50K 9923 treble
3 15A2K 9921 A mid
4 15A50K 9923 bass
5 B50K 9924 Q reverb
6 30C100K 9852 A gain }
7 O5C1M 9923 limiter }
8 T@2B50K 9917 presence } OVERDRIVE
9 B50K 9924 G volume }
and here is a list of what maplins offer in the way of
mini pots

Min Pot Lin 1k JM69A
Min Pot Lin 4k7 JM70M
Min Pot Lin 10k JM71N
Min Pot Lin 22k JM72P
Min Pot Lin 47k JM73Q
Min Pot Lin 100k JM74R
Min Pot Lin 470k JM75s
Min Pot Lin 1M JM76H
Min Pot Log 10k JM77J
Min Pot Log 47k JM78K
Min Pot Log 100k JM79L
Min Pot Log 1M JM80B
Are any of these ok as replacements for any of the broken ones??
It's a fender princeton chorus and I haven't managed to find the
right schematic for it yet :-(
cheers. kev.

Do you have a multimeter? Can you measure resistance?

1 B50K 9924 Q volume = 50k log
2 15A50K 9923 treble = 50k lin
3 15A2K 9921 A mid = 2k ?
4 15A50K 9923 bass = 50k lin
5 B50K 9924 Q reverb = 50k log
6 30C100K 9852 A gain } = 100k ?
7 O5C1M 9923 limiter } = 1meg lin
8 T@2B50K 9917 presence } OVERDRIVE = 50k ?
9 B50K 9924 G volume } = 50k log

I think all the 9924 pots are log
All the 9923 pots are lin
The 9921 (A mid) I think would be lin
The 9852 might be log because it's a gain control

These are only guesses.
You can use a resistance meter and adjust the pots.
An analog meter with a "needle" will be easier to use for this.
As you adjust the pot, see if the needle (or reading on display)
moves in a linear or log fashion.

Good luck with the repair!

Here is a schematic

Fender Princeton Chorus DSP Guitar Amplifier Schematic

rgds

Thanks tunedwolf. Sadly that is not the right one.:-(
I think my sons one is a model before that..

flat5, yes I do have a multimeter. Can you explain how to
go about checking the pots in VERY simple terms pls:-)

with regard to the 2k lin pot controlling the mid range, is there a way
I could use either the 1k or 4k ones that Maplins supply by sticking
a resistor in the way or something? or am I going to have to source a
2k one elsewhere??

Thanks for your time guys.
kev

BUMPING Re this question. Anyone :-)))
with regard to the 2k lin pot controlling the mid range, is there a way
I could use either the 1k or 4k ones that Maplins supply by sticking
a resistor in the way or something? or am I going to have to source a
2k one elsewhere??

Pity, well if I come across an earlier version...

You might get away with a 4K7 dual ganged sub-min pot, just parallel both sections.
This will give ya 2K3 or thereabouts. I would doubt that the additional 300R will make that much of a difference.
Are there no markings on the original pots that would give you a clue as to the manufacturer? Or have you tried a Fender agent for the originals, or a pointer to a supplier? the originals might not be that expensive anyway.

rgds