I recently purchased a non-working guitar amplifier [cheap] It has plastic input jacks soldered to a circuit board which is cracked slightly . The amp makes a motor boat sound , could it be related to the input or possibly a seperate problem?
Quote from: rodman on November 24, 2009, 04:07:30 PM
I recently purchased a non-working guitar amplifier [cheap] It has plastic input jacks soldered to a circuit board which is cracked slightly . The amp makes a motor boat sound , could it be related to the input or possibly a seperate problem?
Could be related to that crack. Is the board itself cracked, just the trace or both? Is the jack still fully soldered to the board?
Also, the motorboating sound is frequently bad power caps most of the time if I recall so that would be worth a check.
Quote from: rodman on November 25, 2009, 11:40:54 AM
I've removed the input jack , [it appears the stress of being board mounted caused the crack ] And soldered in a regular jack using a short piece of shielded cable . One side to ground and the other to R1 where the original circuit board goes [ no change]. The crack is faint , I don't know if it has broken the circuit . How can I check the caps ? Thanks , Rodman
It's best just to replace the caps, they are cheap anyway. Should be less than a couple bucks a piece. Make sure to drain them first (light bulb connected to both legs of the cap) before taking them out.
" The crack is faint , I don't know if it has broken the circuit ."
But that is a pretty important question now isn;t it? Poke the leads from your ohm meter to points on either side of the possible brweak and measure for continuity. That will tell you.
The "stress" of being soldered to the board didn;t break the board. Someone stepping on their guitar cord more likely was what happened. Or posssibly the amp fell on its face while something was plugged into the jack.
As to the problem, it is important that all areas of the circuit needing a ground connection get one. If the board is cracked, a ground trace could be severed leaving some part of the circuit floating. Of course all the traces need to be there, they don;t add extra ones. So while grounds come to mind as they cruise around the edge of hte board, ther are other things there as well.
Doesn;t matter what order an RC is in, but in this case, the cap is in series but the resistor is in shunt.
A schematic that is close should be enough to do the repair with. I don;t even know if Fender published documentation for those. They are "replace only" under warranty, they will not allow us to repair them under warranty. No, I am wrong, it was the only Squire guitar amp schematic in the service files, but there it is. Please note that the clumsy scan is right off the factory service disc, not my fault.
SHould be what you need.
Can you get pictures? It should be simply enough to repair, shouldn't you just be able to bridge over the crack with some solder?