Frontman 15 just buzzes

[John0007]

Found a cheap amp for 20 bucks which worked fine for a couple of years .then all of a sudden the volume controls wouldn't work but you could control volume with guitar control so I took it apart and the normal volume, gain ,and drive volume pots had broken where the bakilite substright leaves the pot.found new ones and replaced them now the thing just has a load hum and nothing works .any one have any ideas what might be wrong

[The Dude]

That could be any number of things. First, measure both AC and DC at the speaker output of the amp and let us know which it is. You could have a shorted output IC, bad or loose filter cap, etc., etc.

[Chuck H]

Since the amp worked (fundamentally) before the work, I would suspect anything involved with the work. Connectors reconnected, any leads that were removed are returned to their proper location, stress to board pads causing failure, cold solder joints due to surface tension, etc.

[g1]

Also, pots usually break like that when the amp does a face-plant. In most cases the input jack or related traces get damaged too.
Did you look at the jack closely and inspect the circuit board for cracks?

[Mick Bailey]

My inclination is to think that in the process of replacing the pots something didn't get reconnected and left the signal path open. Re-check the solder pads and make sure one or more tracks aren't broken and that the joints are good.

[John0007]

Reply to chuck

Since the amp worked (fundamentally) before the work, I would suspect anything involved with the work. Connectors reconnected, any leads that were removed are returned to their proper location, stress to board pads causing failure, cold solder joints due to surface tension, etc.

checked all soldered joints had continuity at all points.board does not have any visual defects looks perfect .I've taken it apart and reassembled mutable times with same results

[John0007]

Would all the input jack solder joints be grounded

[Chuck H]

checked all soldered joints had continuity at all points.board does not have any visual defects looks perfect .I've taken it apart and reassembled mutable times with same results

I'm only observing that the amp "worked" (the volume pot being ineffective was recognized and the reason for the repair) before you did repairs. Now it doesn't. The probability that something other than your work is causing this failure to produce sound seems remote. But it's not unheard of to have a peripheral failure happen at the exactly right moment to make you question your own repair. So it IS a possibility that it isn't your work. But that is still the most likely cause. Don't kill the messenger.

[Chuck H]

Would all the input jack solder joints be grounded

No schematic has been provided, but almost certainly no. If all the input jack solder joints were grounded then the input signal would be grounded and the amp wouldn't work like that. g1 is noting the construction of the amp. The input jacks actually act as supports for the board, relying on the solder connections and board pads. It can compromise the solder joints with even typical use stresses. The pots are actually floating on the board from what I can tell. They aren't even panel secured. That means any use of the pots puts stress on those solder joints because they are the only things holding the pots in place. These issues are very common failure modes for amps of this sort of construction.

[Jazz P Bass]

Would all the input jack solder joints be grounded

The only pin of the 9 pins of the input jack that is at ground potential is the sole lonesome one at the top.

Here is a copy of the G & the R Frontman 15 service manual.

Frontman 15G & 15R Mexico.zip

[Chuck H]

Here is a copy of the G & the R Frontman 15 service manual.

It's absolutely GREAT that you're so good at, and vigilant with locating and posting the circuits in question on the forum. It's been an asset to be sure, but... Sometimes I think a man should arrange things for themselves if they wish to progress. I did look up the schem, but I was trying to encourage the OP to be proactive to an appropriate level of accountability on the matter. Which seems only right since (probably) none of us have a broken Frontman 15.

[Jazz P Bass]

"Which seems only right since (probably) none of us have a broken Frontman 15. "

Actually, I do have one right in front of me.

[Chuck H]

Actually, I do have one right in front of me.

Bowing and stepping backwards

[g1]

Would all the input jack solder joints be grounded

It's possible they may measure like this if you have nothing plugged into the input jack. Plug a cord in there with nothing connected to the other end. Do all the jack contacts still read short to ground?

[Jazz P Bass]

It's possible they may measure like this if you have nothing plugged into the input jack. Plug a cord in there with nothing connected to the other end. Do all the jack contacts still read short to ground?

I just checked the one that I have.

With no input, the only ground connection is the top pin.