Troubleshooting a microamp

[PeterJ]

Hi, all - I have a mid-2000s MXR microamp that's been acting up lately. When I step on the switch (a Carling DPDT), the volume mostly, but not completely, cuts out. Some sound still gets through, but the volume knob makes only a tiny bit of difference.

Is this most likely a switch issue? Is the answer simply replacing the switch? I've done some simple builds, so I'm not afraid to solder, but I don't want to start dissecting without some ideas of where to go. The paint flakes off these MXR boxes if you look at them wrong...

Thanks for suggestions.

[GibsonGM]

The first thing I'd check, with symptoms like that, is for a loose solder connection between switch and board. After that, yup, bad/dirty switch.

So, I'd re-flow the switch contacts at the PCB, and then try it out....lightly (carefully!) flex the PCB with a pencil eraser while engaged, to ensure that the issue is fixed.  Should take 10 mins. to know if that's it...

[PeterJ]

Cool! I'll give that a shot and report back. Thanks!

[ElectricDruid]

Have a look for cracked tracks on the PCB too, especially if the switch is PCB mounted. If the switch is a bit loose (or has been in the past) then the board gets flexed when you step on it and eventually the tracks crack. This can be a pain to find since often the problem is intermittent and only shows up when the board is flexed.

HTH,
Tom

[PeterJ]

I played around with it, and the sound comes back intermittently if I gently wiggle the plunger side to side. I did reflow the solder joints on the switch, with no change. I'm thinking I just need to replace the original Carling switch itself. I will try flexing the board before I do the surgery, though. Thanks for the tip.