Fender Bassman 250 no output.

[Randall]

So I get this Bassman 250 in for no output. Fuses are good, quick check of outputs shows nothing bad. Signal is good to Preamp output jack. I check the rails at the outputs, and get nothing. Start from the beginning, I have them both at the rectifier, but they both stop at the filter caps C18/C19. In other words, they get to the top side via the wide traces, but neither gets through the hole to the trace on the bottom side of the board. The negative rail I could get through with extra solder, but the positive side is a no go. Not wanting to rely on a solder blob, I ran jumper wires under the board from where the black and red wires connect to the board, to the respective legs of C18/19, sending both rials on their merry way. This post is not so much asking for assistance as it is wondering out loud how unusual it is for both rails to fail in the same way in the same place. Perhaps those big filter caps dislodged the copper through traces, but odd that it happened together?

fender_bassman_250_fba_schematic_rev-a.pdf

[g1]

Any chance those caps have been replaced? Some times people tear the vias out when replacing components.

[Enzo]

It is unusual for ANY particular failure to be exactly the same on most anything. On the other hand, there may be clues. If two filter caps stick up from the board together, and something smacked them, they might have been torqued sideways together and both snapped a via or other trace. They are next to each other, and often they are glued together. Are yours?

Some things are very rare, but you can never assume they won't happen. They just sit farther down my list of likelihood. Best not to think in terms of what are the odds. Better to think in terms of what is wrong, what is needed to fix it, and then do that.

[Randall]

They were not glued together (they are now). The vias were not ripped out, they were just not conducting. Maybe they were both smacked sideways, or dropped and snapped the connections. At any rate, it's working now.

[Enzo]

Well that is what is important of course.

The vias don't have to get ripped out, they only need to get cracked.

[J M Fahey]

Perhaps those big filter caps dislodged the copper through traces, but odd that it happened together?

Metal inside vias is *microns* thin and not directly attached or epoxied to PCB base material but deposited on a microns thin *graphite* layer , which is both very soft and lubricant.

The point is that plated through holes or vias are relatively easy to pull.

No mechanical stress on standard layer to layer vias, BUT if also used to hold heavy capacitor legs, we might have a problem.

As of 2 random failures happening at the same time, I agree that itīs statistically very unlikely ... but replacing caps affects both legs at the same time; replacing 2 caps affects 4 holes within minutes , so I can easily see rough handling as the root of this problem.

Dropping from a table or cabinet top also counts as a "simultaneous" event