Issues with Printed Circuit Boards used in Guitar Amps

[SoulFetish]

That’s a good point. It makes sense that the I would be seeing components exhibting some kind of failure. Those are the amps needing repairs. No one is going to spend a couple of hundred dollars to have me not repair a perfectly working amp.
Well, if they they bring in a perfctly working amp, then the problem is almost certainly between the guitar and the floor.

[loudthud]

I don't know where to start with all the comments so far, but thanks a bunch.

Just going by what I've read here and on other sites, board mounted pots and jacks frequently have fractured connections to the PCB and replacements are hard to find after a couple of years. Even spraying the pots can be a pain because the only place to spray the cleaner is between the pot and the PCB. I like R. G.'s idea of using conventional pots on short wires to a PCB like he used on the Thomas-Vox replacement boards. Also, the idea of a removable panel under the PCB is very good. I have an old Ampeg B25 like that.

One of the amps that seems to have a bad reputation is the Fender FM212. The snap-in filter caps frequently have fractured solder connections on the PCB. I see a lot of threads on that amp but I have never opened one up myself.

Some years back there were always lots of complaints about the cables interconnecting PCB's. Most used a type of "insulation displacement" system. Is this still a problem with newer amps like Fender Hot Rod and Blues series?

I don't like double sided boards if wires have to solder directly to the board. Eyelets are many times stronger that thru holes if you have to solder and un-solder wires more than once or twice.

Yes, I build custom pad stacks and components (is there any other way?) for all my PCBs. I downloaded this PCB software that was supposed to make it easy to order boards from vendors in the US and China. It totally sucked. Cryptic names for all the footprints, I couldn't find any components I knew. Even a 1206 surface mount resistor couldn't be found. Couldn't figure out how to make my own components. I'll stick with Tango that I paid $800 for back in the 80's. Problem is the Gerber files it makes need to be converted to current standards.

On the design I'm working on, it's solid state so building the whole thing on an eyelet board isn't practical. All wires that go off board get eyelets. All 2WFP resistors get eyelets and I mount them up off the board. All 5W and 10W box resistors go on turrets. The main reservoir cap is on the main 2.5x10 inch PCB because it has a 4 way star on the ground pin. On the prototypes I build there are several ground wires that go to the power supply board.

[Enzo]

The Fender FM212R is just one example of what I myself call the Fender Wedge Chassis. I call it that because the chassis is a bent sheet. The front is only as deep as the panel control strip, maybe 2", but the rear panel is more like 8" tall. So seen from the end, it is wedge shaped. They made a number of models laid out like that. The big main board sat on the sloping bottom panel. Obviously solid state amps.

The two main can caps for the V+ V- rails sat in the middle of the board mostly, and stuck up into the air. My personal theory was that that large sloping flat panel was in the backwash of the speakers and so gave the caps a good shake. Even though the caps usually had silicone daubed between them, they still liked to crack their solder. Resoldering the main caps became an automatic step on all wedge chassis Fenders in my shop.


I don't think it was the snap-in-ness of the caps so much as it was the layout.

[Gregg]

...board mounted pots and jacks frequently have fractured connections to the PCB...

To avoid that for home builds you can insert the pots in the PCB, tighten them first to the front/back panel and then solder them in place if you can reach them with the soldering iron. This way you can eliminate some of the mechanical stress on the pots.

[SoulFetish]

FWIW, After working on a couple of GK amps, I remember thinking that they had very nice quality pcbs inside their amps. I could just be a sucker for thick, blue FR4 boards. So, maybe some of the more experienced technicians have worked on more of them than I have.