Marshall MG10cd & Fender Frontman 15G

[DrGonz78]

I have acquired these little amps as a means to play w/ them and fix things that might be wrong. I found these all dusty and a bit neglected, yet still in decent condition.($5 deal). Cleaned them both up, both powered up and they sound pretty good actually. There are issues w/ the pots on both amps.

The Fender Frontman had issues w/ the first 3 pots, 1- Volume 2- Gain (both for the overdrive channel), 3- Volume (for main clean). All the pots cracked at the plastic part that connects to the leads on the board. I was just curious to see if super gluing the plastic back together would at least allow the pot to work. Which I found out it won't... Is this true? or could it be something else to look at... The switch between clean/od is also not working when I click OD results in no signal(this might not be a bad switch). Clean works good but can't control volume now. Anyhow, just wanted to ask if you can fix (glue) the pot in this manner to get it to work(theoretically)?

So, the other amp I am playing w/ is the Marshall MG10cd. Now this one had two really damaged pots. I removed them to attempt to rebuild it... Just doing this for fun now so don't laugh too hard at me... So I opened the pot up and saw how cheaply built these are... Plastic holding steel and the plastic lost the battle(the part that holds spinning knob in the socket). So I somehow super glued the plastic part and got the two pots in a working order. Soldered it to the board but still it won't work. My question also here is that one of the pots was a 50K pot and the other a B5k. I think in this case that I may put the 50k on the Contour knob and put the B5k pot on the Volume for the OD channel. The Clean sounds great already and that pot works. The OD switch works on this one but only the gain knob is working and I get very little volume. So I am gonna open it up again now and look at the pot that is on the volume (clean) to see if it is 50k, then switch it back.
UPDATE:
AMP POTENTIOMETER>>> CLEAN = A5K, GAIN = G1M, (VOLUME = B5K, COUNTOUR = A50K) the last two are the ones in question.
I am pretty sure that I put them back on in the right place. Now opening up the inside of the amp I notice I put the back metal part upside down, so that might be the problem too. Will fix and test tomorrow.
End all: How do we find out information as to what pots are on any amp in general? Are there references to look up what pots are originally on an amplifier?
Thanks for reading take care~

[52 Bill]

Broken pots on those amps are a very common problem. These amps are manufactured so cheaply, that they are usually not repaired under warranty, but are just tossed and replaced when they break.

If the backing wafer is broken, it is likely that the resistance element has broken as well and there is no longer any continuity between the two outer pins of the pot. These can't be easily glued back together so replacement is the only fix. Do you have an ohm meter available to test your pots?

As for what pot goes where, you can find this out by looking at the schematic drawing of the amp that you are working on. It will list all of the parts and show how they are interconnected to make the circuit of the working amp.

In repairing your two amps, I suggest that you replace the pots before you do anything else like messing with the channel switch etc. The broken pots will basically open up the audio path causing the signal to drop out in part or in total, as you have described.

Good luck.

[Enzo]

I guarantee that if the brown plastic wafer is cracked across, the pot is gone and must be replaced. You can't glue it back together any more than you can glue a broken light bulb back together.

Small practice amps like those usually belong to inexperienced owners, who knock them over, step on their cords, or let things fall on them. Smack the knob, and it pushes the shaft back into the pot, snapping the wafer.


The amplifier's schematic tells you what values of pot are used.

Order the right parts from a supplier and replace the broken pots.

[DrGonz78]

52 Bill & Enzo,

Thanks for the responses! Yeah it was just my attempt to see if I had steady enough hand to try to rebuild the small little pots parts back together again. Both attempts were failures but yet I did get to see how simple a potentiometer really is and how it is put together. I am wondering if there are parts online to rebuild pots and/or make your own pots. This way I might be able to order large quantities of these to rebuild my own pots for future repairs as I collect more amps. Probably, best just to order them as they come but just a thought.

I think my multimeter is toasted since it blew a fuse! lol I am gonna buy a new one on sunday and start working on a few different amps. Thanks again for the feedback, again you answered my questions perfectly.

~DrGonz

[Enzo]

Uh... no. No one sells pot parts. There is no market for them. I operate a pro audio repair shop. My basic rate is $60 an hour - a dollar a minute - for labor. Our member Frondelli is in Manhattan and their rate is twice that amount. I get them cheaper than your do, but let us say a pot costs $3. If I could "fix" one in under three minutes, I suppose I could save a dollar. And then I would have a fixed worn one, not a new one.

One thing about stocking parts. I can pretty much cover resistors, and even caps, but pots? No way I can stock them all. Even the same basic pot might have support wings at Fender and not at Marshall. COuld be a split knurled 1/2" shaft for one model, and a solid D-shaft elsewhere. 12mm? 16mm? 24mm? Tapers - linear, audio, reverse audio, center taper, etc. Pots are custom ordered for amp makers. If you get the ALps catalog, you will find it is a chart that helps you generate a part number. The part number then describes all the atributes of the pot, which they then make for you. Yes, you would be ordering 10,000 of each.

And just like repairing a pot, building your own from parts would be much more expensive than just buying pots. Unless your time has no value. And ask anyone in the auto business, how much does a $25,000 car cost if you buy it as parts? $100,000? $250,000? Large multiples of the complete car cost.

[drewl]

I usually end up with a bunch of these amps with nothing wrong but broken pots or cracked solder connections.
Just replace the pots if you want, they're usually under $2 each if you order ten or more which I do as I know I'll need them for something or else.

[DrGonz78]

Yup I figured this much after reading your posts. Just curious to learn any information about amp repair and appreciate all the advice.

[J M Fahey]

The *only* way to make it worth, is on very special occasions, as in not having the physically right one, but having same resistance and curve ones on he shelf.
Since it takes me 1 hour to get to Downtown , say, 30 minutes lost at the Shop, and another hour back, if I´m not needing anything else and I have the customer hanging from my neck, it pays me to lose 15 minutes doing some surgery switching tracks, since most 16 mm (as an example) carbon tracks are physically about the same.(not always, eh?)
We are not talking part cost here, which is irrelevant, but actual time spent.
But, as I said, it must be a *very* special situation.