Fender Princeton 65 drive channel problem!

[doofus4000]

Hi

I have a Fender Princeton 65 amplifier (1999) and have had it in storage for the past 5 years.

Pulled it out and starting using it again and the clean channel sounds perfect.

Whenever I change to the drive distorion channel by pushsing the little button I now get nothing. If I fiddle with the drive and volume knobs so that they are very low around number 1 I can get an acoustic guitar sound. If I try to turn the volume knob up it just gets really loud really quickly with no distortion. If I turn the drive knob up the sound stays acoustic and eventually there is this 'pop' sound around knob number 4 or 5 and I then get no sound at all when strumming the guitar, just a faint background hiss, turn the drive knob back down and I can get it back to an acoustic sound.

Anyone know what my problem could be?

Read up on different posts on the forums and most people are saying to check all the soldered connections on the bottom of the PCB. So I have got to the underside of the PCB (major pain in the ass to take it all apart btw) and everything looks ok apart from one piece of soldering which looks like it has been resoldered at some stage but it just corresponds to the little drive channel light on the top side of the PCB.

Can anyone help me?

Many thanks in advance.

[Enzo]

Perhaps that control itself is either broken, cracked or open at one end.

[doofus4000]

Perhaps that control itself is either broken, cracked or open at one end.

How do you mean 'cracked' or 'opened at one end'?

Do controls like this often break/break easily?

If it was that the control was broken what would recommend that I do..could I use one of the other knobs and see if it cures the problem maybe?

[Chuck H]

Don't use one of the other pots to troubleshoot. It is hard to say what circuits share what. Disabling another pot could cause additional and confusing symptoms.

If the amp worked when it was stored I would say to start with a good cleaning of all the jacks, pots and switches. All of them. Footswitch and it's plug included.

Info on cleaning components and what to use is available here by searching other threads.

I've "fixed" many amps that quit working after they were put away for awhile in working condition by simply cleaning oxide from the moving electrical contact points that can develop during storage.

[doofus4000]

Don't use one of the other pots to troubleshoot. It is hard to say what circuits share what. Disabling another pot could cause additional and confusing symptoms.

If the amp worked when it was stored I would say to start with a good cleaning of all the jacks, pots and switches. All of them. Footswitch and it's plug included.

Info on cleaning components and what to use is available here by searching other threads.

I've "fixed" many amps that quit working after they were put away for awhile in working condition by simply cleaning oxide from the moving electrical contact points that can develop during storage.

Thanks for the reply. But would the cleaning on the jacks etc help saying the acoustic clean channel works perfect?

[Chuck H]

It sounds to me like there may an out of phase and possibly oscillation problem happening when the drive channel is selected. It's hard to say without a schematic, but there could be a dirty jack switch or footswitch connection that is keeping the channel from doing what it's supposed to.

If the amp worked when you put it away, and it hasn't been dropped, flooded or loaned out, "I" would start by cleaning the electronics.

[doofus4000]

It sounds to me like there may an out of phase and possibly oscillation problem happening when the drive channel is selected. It's hard to say without a schematic, but there could be a dirty jack switch or footswitch connection that is keeping the channel from doing what it's supposed to.

If the amp worked when you put it away, and it hasn't been dropped, flooded or loaned out, "I" would start by cleaning the electronics.

Ok, I will give it a good clean as you say and see if that gets me anywhere. Many thanks for the info!

[Enzo]

How do you mean 'cracked' or 'opened at one end'?

Do controls like this often break/break easily?

It doesn;t matter if they do it often or not. All that matter is whether it happened here or not. It doesn't often happen that grand pianos fall from buildings, but if one falls on you, you are dead nonetheless.


The controls comprise a phenolic wafer or something similar, a shaft assembly, a contact assembly, and a housing. And that wafer has a resistive stripe around it. The contacts bear along that stripe to make the variable resistance. You see the wafer where it stick out of the housing, and the three legs are attached. SOmetimes a control snaps its wafer - the part where the legs attach is actually broken away from the part inside. That is cracked. Open means an electrical circuit path that is open. If the resistove stripe for some reason no longer makes contact with one of the legs, then the pot is open.

[doofus4000]

ok so I got a multimeter and checked all the controls, the drive control was not allowing any current to flow through it so guessed it was broken and got a new one (100k variable resistor). Soldered it in and it works! Thanks everyone for your advice.