My Fender Frontman 25R guitar amp.

[rose62]

Good day, all. I'm Steve from west of Atlanta and I've got a guitar amplifier problem. I see that there is another forum for "repair." Should any questions be directed there? Thanks.

 

[rose62]

The amp will only produce sound through the gain channel. On the "clean" channel, at full volume there's barely a whisper. If I use the push-button on the control panel or the footswitch, the LED indicates that the channel has changed. And the volume and gain (distortion) controls both work well in the overdrive channel. Also, even when I'm on the "clean" channel the overdrive knobs control the sound. Attached is an image of the device removed from the cab. I put a meter on all the pots to see if they're changing states and to compare to each other and they all react the same. I don't know how to test the push-button installed. It would seem that although the light associated with the push-button indicates that it's changing channel the switch may not actually be doing so.

 

[Nigel Goodwin]

You could try swapping U1 and U2 over, see if the fault changes to the overdrive channel, it could be that U1-B is faulty. Or if you have a TL072 to hand?, replace U1 and see if that cures it.

The channel switching is done electronically, so if the LED goes ON and OFF then all is well with the switch.

 

[unclejed613]

either part of the forum will do... this part of the forum is kind of a "catch-all"... what problems are you having with the amp?

 

[rose62]

What are those parts and what do they do? Could I simply use some braid and remove and swap? How much heat can they take? They're identical, yes?

 

[unclejed613]

looks like your clean channel got something spilled on it. so some of the parts near the spill maybe corroded or damaged from the liquid causing a short circuit... maybe a picture of that area from directly above the board would help...

 

[Nigel Goodwin]

What are those parts and what do they do? Could I simply use some braid and remove and swap? How much heat can they take? They're identical, yes?

Yes, they are identical - and if you wanted you could fit sockets, and swap them about easily after that. One half of U1 is common to both channels, but U2 is only used on the over drive channel.

 

[rose62]

It looks like the TL072 is pretty cheap and available. Would it be a good starting point just to replace them? By the way, thanks for the input, everyone.

 

[Nigel Goodwin]

It looks like the TL072 is pretty cheap and available. Would it be a good starting point just to replace them? By the way, thanks for the input, everyone.

Very cheap and very available, but it's only U1 you need to try changing - U2 is used on the over drive channel only.

Nice thing with Fender, they make Schematics available on-line

 

[rose62]

"Nice thing with Fender, they make Schematics available on-line."

Yes, that would be helpful, if I knew a damn thing above the most very basic things about dc circuits!

 

[rose62]

So, I'm going to order the part. Yes, I am. I must. Had a jam last night and the thing works like it should? What in the world?

 

[rose62]

The amp has continued to function properly except that in the clean channel, which didn't work at all initially, is not real responsive when the channel knob is turned very low. But other than that it's all good. Does anyone have a theory about why it would suddenly begin to work? I hadn't used a pedal to switch channels for quite some time, using instead the push-button, and hadn't used the clean channel nearly at all for over a year.

 

[unclejed613]

there could have been oxidation in the switch, or whatever it was that appears to have been spilled on the PCB could have dried up... another thing that has become common is tin whiskers in switches, etc... for about 2 or 3 years Denon AV receivers were plagued with tin whiskers shorting a pair of switch contacts in the headphone jack, which would turn off the speaker relay.... they replaced the headphone jacks with a non-RoHS version, and the problem stopped happening.