Fender Frontman 65r

[mississippi]

I have got a Fender Frontman 65r with the following problem.
When the amp is switched on after a while you wil hear a crackling noise.
The time between the crackling noises and the clrackling time is very random.
The schematic diagram is available. Does somebody have an idea where to look and find a sollution??
Thanks in advance.
Regards, Mat.

 

[firechief]

For best results you should post the schematic with your question. Try pulling out the first pre-amp tube and report if it crackles.

 

[mississippi]

Ok, here is the schematic diagram of the amplifier.

 

[firechief]

OK that helps. Needless to say that you should not pull out the "tube" Try this- Plug a phone plug into J4 "power amp in" jack. Just a cable with nothing connected to the other end. This seperates the pre amp section from the power section. If the crackling noises no longer happen then the problem is in the pre amp section. This electrically breaks the amp into two sections and pronvides a clue as to where to look. If you touch the other end of the cable pluged into the power amp you will probally hear a bad noise. That is normal and wont hurt anything. Report back.

 

[jaycee]

try and isolate the problem - is it in the preamp or the power amp stage?
crackles are typically a sign of dirty wipers on pots, bad contacts in sockets, or dry solder joints

 

[Bare]

OR compromised Capacitors.. Not unlikely after 50 years

 

[mississippi]

Thanks all.
@Firechief: The problem must be in the power section. After separating it from the pre-amp section the crackling was still there.
@ Bare:
This amp is from 08-2005. This is too short for 50 years.

 

[JMFahey]

Crackling usually comes from a bad/poor/intermittent contact "somewhere".
Most possibilities are in the preamp section, simply becouse you'll find most pots/jacks/switches there; not that many possibilities at the power amp.

If crackling "comes from the Power Amp", *maybe* you have a speaker tinsel wire problem.
Connect amp to another speaker to check that.

*If* not, and your crackling effectively comes from inside the Power Amp PCB itself, it can only mean some cracked solder or track, a pesky problem to find.
Tap all over it with a chopstic or plastic Bic pen or similar, part by part, and then push it here and there, making it flex *a little*, maybe you get lucky causing the crackle or a pop at will.
If so, resolder all around the suspect spot with *a little* solder and a good iron.
Avoid bridging close up pads, making blobs, etc.

Good luck.

 

[mississippi]

This weekend I will solder als spots, and I will look after bad contacts.
You will hear from me afterwards.