Amplifiers contain voltages high enough to Kill you even after the amp has been powered Off !!! If you don't have enough electronic experience to identify and discharge the Filter Capacitors which contain these Deadly voltages, take your amp to a Qualified tech. If you don't know a qualified tech in your area, post a request in the alt.guitar.amps newsgroup, the folks there will be happy to help you.
HOWTO:
1. The items you'll need are:
2. Strip the wire on one end and attach the alligator clip (solder it on if you can). Then cover that soldered connection with heat shrink.
3. At the middle of your length of wire, cut and strip each end. Solder in the 150-Ohm 10 watt resistor. Then cover the resistor and the solder connections with another piece of your shrink wrap.
4. On the remaining end, slip on a piece of heat shink. Attach your multimeter probe (solder it on if you can). Then shrink the heat shrink over the connection.
6. Pull the chassis out, being VERY Careful not to touch anything inside yet.
7. Clip the alligator clip end of your discharging probe to the metal of the chassis, making sure it's good and tight.
8. Now go through the chassis with the probe end and touch the + side of every cap you see.
9. That's it !!!