Members blindopher Posted June 27, 2014 Members Share Posted June 27, 2014 hi, I need to do a fix on my amp: MOD 102 - a DIY 5W SE class A head Here's the schematic: http://www.modkitsdiy.com/sites/default/files/product_files/mod_102_schematic_0.pdf I know the filter caps are rigged with bleeders, but me being on the paranoid side, I would like to be able to drain them if by some unlikely chance the bleeders are fried. If need be i'll jumper a preamp tube plate pin to chassis and measure voltage, BUT what about the OTHER caps - do they present potential danger? Aside from the 3 power section filter caps (which are wired in parallel, correct?) there are 3 other smaller electrolytic caps which also appear to pack a nice voltage, and bypass caps and coupling caps. To sum it all up, can I TOUCH anywhere inside the amp if the 3 filter caps are drained below 10V and the amp is unplugged? I just want to be as safe as I can - this is my first amp project (i've done a pedal before) thanx P.S. another link to the amp page http://www.modkitsdiy.com/kit/mod_102_guitar_amp_kit Link to comment Share on other sites More sharing options...
Moderators AMZ-FX Posted June 27, 2014 Moderators Share Posted June 27, 2014 1. Unplug the amp.2. Wait several minutes for the bleeder resistor to do its job. Two or three minutes, not 15 seconds!3. Use a multimeter to measure the voltage at B1 or B2. If B1 or B2 is high voltage: 100v, 200v or more, then the bleeder resistor is defective and should be replaced. Bleed the voltage off B1 or B2 with a 220k resistor then go to step 4.4. The voltage should be close to 0v. If it is above 0v but below 15v then use a 1k resistor in series to short B1 or B2 to ground. If it is over 15v then use a 10k resistor.5. Work on the amp. Once you have the caps drained to 0v you are good to go, and you can leave a wire clipped from the power rail (HV, B1 or B2) to ground, if that makes you feel better. Proceed with caution... but you seem to have plenty of that! regards, Jack Link to comment Share on other sites More sharing options...
Members blindopher Posted June 27, 2014 Author Members Share Posted June 27, 2014 Got it! thanx! Link to comment Share on other sites More sharing options...
Members Maveric Manic Posted July 4, 2014 Members Share Posted July 4, 2014 Just keeping the Standby switch On for 3 minutes with power off and unplugged from AC will discharge as well but I check it with a voltmeter. Link to comment Share on other sites More sharing options...
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