15-03-2014, 09:39 PM
(15-03-2014, 08:54 PM)richard296 Wrote: If the resistor got that hot in use there was hardly no ventilation for the heat to dissapate or flow. As earlier mentioned the alloy case is inverted trapping the heat and the vents were none existant. It's no wonder it burnt out. richie. ps the amp was working fine so where do you reckon the problem could be nothing seemed to get hot on the boards the only thing i didn't check for heat was the transistors on the alloy heatsink in the amp.
Yes, a scorched printed circuit board isn't always indicative that a resistor has been subjected to an excess current flow through it as many service tech's will confirm.
You mentioned earlier that you did have a signal playing through the amp and it sounded ok but after a while it went distorted.
Normally one would expect the output stage to be the cause of the problem but not exclusively.
Try powering it up again with a signal input, if it sounds ok at switch on again then check straight away the voltage on the collectors of both the power output transistors (2N3055's) the case of the transistor is the collector, if you carefully hinge up the printed board the collector is the connection via a solder tag to one of the nuts and bolts that secure the transistors, the collectors should be insulated from the heatsink, if the heatsink happens to be earthed then be careful with you meter probe when measuring the collector, you don't want to short anything out, make a note of the two readings.
Leave the amp running until the sound goes distorted as it did before and quickly measure the two collector voltages again and make a note and switch off.
Lawrence.
