FENDER frontman guitar AMPLIFIER repair

Thread Starter

Plato69

Joined Apr 23, 2020
2
Hello there, i'm new to this forum so please let me know kindly if I do something wrong/disattend this forum's rules etc..

So i ran into this old amplifier looking for junk in a basement and i took it. It still worked pretty well except for a quite loud background noise and some annoying problem with ne normal volume potentiometer (or at least so i thought initially)

This is the circuit schematics of the device I'm talking about

https://idoc.pub/documents/fender-frontman-15g-15r-guitar-amplifier-schematic-qvnd60wyor4x

So, to reduce the background noise I removed the reverb unit and that seemed to help a little.

About the normal volume potentiometer I ran some tests with my multimeter and it looked like a perfectly fine working logarithmic potentiometer but I still have this problem with volume that quickly escalates from nothing to super loud just by opening it a little bit (let's say 1/10 of the whole ride) I don't know what happens if I turn the knoob even further because the loud noise is already unbearable at that level.

I tried testing some of the capacitors directly linked to the normal volume and the main input part of the circuit but I only have a basic multimeter so although high capacitance capacitor seemed to work fine (by running a "resistance to infinity" test) the small capacitance ones were basically untestable.

Lastly I still have some background noise which at this point i think might depend on some defects on the main input part of the circuit.

Do you guys have any idea how to approach this reparation project?

Thank you in advance for your time

Plato
 

MrChips

Joined Oct 2, 2009
21,400
Please describe the noise you are hearing.

Be prepared to buy a new volume control pot.

In the meantime, you can try spraying the inside of the pot with control cleaner. Work the pot back and forth while the cleaner is still present (while the power is off).
 

Alec_t

Joined Sep 17, 2013
11,419
After a long period unused there's a good chance the contacts in any plug/socket/switch will have tarnished/oxidised. I'd try contact cleaner on all those contacts.
 

Thread Starter

Plato69

Joined Apr 23, 2020
2
The noise I hear is basically just a white background noise (maybe some peaks on the higher frequencies end of the spectrum)

I must say the amplifier itself works i just need to be careful to set the knoob just to the right position or I might go deaf (or end up out of the amplification range, so basically unamplified, very subtle sound that blends in with the background noise).

I will try the contact cleaner but i'm not sure it's the right move since measuring resistance for different configuration of the pot. gave me a pretty solid logarithmic progression.

Can something be wrong with the IC4560?
 
Top