Eugene Noise Fest is right around the corner, and I've the intention of providing sound this year. This essentially equates to my window of procrastination coming to a close as I assess the pile of amps and consider my buried PA speakers. I have three weeks to get my shit together.


First up is a Soundcraftsmen RA7502 power amp. This unit would pull brownout levels of current off the wall for a split second and crowbar into protect mode, cycling through those two states every four seconds or so. I contacted a forum member on audiokarma.org who used to work on these Class H amps and described the symptoms. He stated that's usual behaviour for a shorted power transistor or drifted components in the protect circuit.


Here's what I take to be the audio stages hanging off the actual power stage, more or less freed up from the power supply section. Power amplifier stage as follows:


Turns out I have a cooked output transistor. Thankfully the protection scheme in these amps is fast enough that I only lost one active as opposed to the entire rail.


Now to determine if this is a Toshiba 2SB554 or a Toshiba 2SD424. Hmmmm