Odd Amp Repair

[JKRamsey1991]

So my single channel no effects AB763 that I built a couple years back developed really bad blocking distortion all of a sudden. This amp has been played a lot and carted around in my car a lot as well. Pulled the chassis out and chopsticked the main board and found nothing. Did redo a couple small things that I just use better practices now than I did then but no real issues. I then pulled the doghouse. One of the 80uF series caps in the power supply had somehow managed to break a leg. Now this is in a doghouse the cap soldered to an eyelet board and setting firmly on the eyelet board. I have no idea how the leg broke on it. Soldered in a new cap and shes back in business.

Still curious how the leg broke though.

[jim]

I think it is vibration related.  When you repair it make sure its flat on the circuit board and not suspended by the leads.  Jim

[JKRamsey1991]

I think it is vibration related.  When you repair it make sure its flat on the circuit board and not suspended by the leads.  Jim

I'm def going to. Also going to silicone it down to make sure.

[jjasilli]

Some recent Posts have extolled the virtues of putting play or give in cap leads.  Best practice is to do that for all component leads.  That way there's some give when confronted with vibration, heating & cooling.

[Tony Bones]

That might make sense for stationary equipment, but anything that's subject to a lot of vibration (like riding around in a car) will wobble back and forth. If unlucky, a lead will fatigue and break.

I suppose what would work is to leave a service loop (i.e. a vaguely "S" shaped bend) in each lead, but fasten the device body mechanically so that it can't vibrate.

Designing to withstand harsh environments, including vibration, is a somewhat evolved science. Generally speaking, just letting things flop around by their leads is never a good idea.

FWIW, I have built engine control computers for cars and would never use solid core wire anywhere in a car. It's guaranteed to break eventually. Solid leads on components can't be avoided, but I tend to prefer SMD in those applications anyway. 

[jim]

other things to consider--avoid multiple try 90 degree home run bends--get it right the first time.  Bending-straightening cycles work-hardens the leads (like bending a coat hanger many times) They get brittle.Softer rounder bends will preserve the strength of the leads.   Larger axial lead electrolytics are particularly sensitive to lead fatigue right where the wire joins the body.  Jim