What is wrong with my amp: part 2

[cstockdale]

Thanks for the help last time around. I simply have had very little time to play this amp lately (I have a 10 month old baby: most of my playing these days is acoustic or POD). I was playing tonight through the Hot Rod, and there is that damn crackle again.

Opened up the back of the amp and check this out:

I turned out the lights to see if I could see any shorting etc as I played, and saw sparks from high heaven. Where the plug in is to attach an external cabinet (I don't use an external cab) there were sparks like mad. Turned the lights on, and saw a little screw rolling around making contact with the plugin. Every time the screw hit the plug, sparks, and crackle sound.

So, where did that screw come from ( I know I have a few loose)? There are 6 screws that hold the circuit board inside the amp chassis. Only one of them is still there , 4 are rolling around the tray at the bottom, one is missing altogether (I bought this amp used). Now, it seems easy enough to screw them back in, but after the warnings about high voltage capacitors being able to kill you, I don't want to touch a thing without asking first:


how can I be sure the capacitors are no longer holding a charge?
what do capacitors look like so I can avoid touching them?
Has this ever happened to anyone else?

 

[Tadpui]

A capacitor will be recognizeable as a small cylinder that will probably be standing on end on the circuit board. It'll have a number accompanied by either the letter 'f' or 'μf' (ferods or micro-ferods, being a measure of capacitance).

I don't know of a way to determine if a capacitor is holding a charge...I think the only way to know is to discharge it, and usually that's done the hard way (brizzzaaap!).

Maybe invite someone over that you don't like very much and have that person screw them back in. Is your mother-in-law busy tonight?

 

[cstockdale]

I found a way on the net for draining the caps (not completely, but enough to avoid any real pain)... just for those interested I got this off of a site that gave very detailed instructions for doing your own amp mods:

with the amp on and warmed up, don't power it down with the power switch or standby, just yank the plug out of the wall, and keep strumming until the sound dies away: then your caps are drained.

I still avoided touching them just for safety's sake, but now the screws are all back in, and I discovered half the screws in teh amp were loose, I tightened it all up, and voila: she is sounding hotter than hell again.

 

[Chill]

That's a good way to get the voltages down to 10-20V or so. I also made a cap discharging tool with an insulated clipper lead from Radio Shack: cut it in half, solder in about 1K of resistance with 1W, electrical or liquid tape over it, and voila, clip on a cap in the middle of the supply, wait 30 sec and measure the voltages. They should be in the mV range.

And check out The Unofficial HR Deluxe owner's page: http://studentweb.eku.edu/justin_holton/