this one was blowing fuses -
i was getting a short across V+/V- - traced it to the MOSFETS on the little breakaway power amp PCB. fortunately or not, the FETs are the pretty much the only non-SMD/miniature parts on that board - so it was possible (although hard) to replace them. i did. amp worked! phew. put it back together - BAM - another fuse blown.
checked the FETs, two of them - q10B and q11 - had blown, but not q10.
took the power amp board out, turned the amp on with a limiter in series - all good. at this point i figured it must be something else on the power amp board - SMD bullshit - so maybe time to give up.
BUT, there is one weird sympton that id like your guys' help with: even with the bad FETs out of there/the power amp PCB unplugged, when i turn the amp on, my limiter will sometimes glow really bright (like full on short bright) for a split second when i turn it on. it blew a 3A slow blow fuse (with the power amp/shorted FETs out of circuit) once, even. it does not do this every time. sometimes i turn it on and i get a normal dull bulb for a second that gets even duller after the initial switching on. but, like i said, SOMETIMES the bulb will light like there's a short but just for a second.
what's going on here? something is causing the current to spike but only sometimes and just for a second.........any thoughts?? bad rectifiers? bad filter caps? so hard to tell because otherwise it works! voltages/ripples,etc look fine!!
hmmmm
i was getting a short across V+/V- - traced it to the MOSFETS on the little breakaway power amp PCB. fortunately or not, the FETs are the pretty much the only non-SMD/miniature parts on that board - so it was possible (although hard) to replace them. i did. amp worked! phew. put it back together - BAM - another fuse blown.
checked the FETs, two of them - q10B and q11 - had blown, but not q10.
took the power amp board out, turned the amp on with a limiter in series - all good. at this point i figured it must be something else on the power amp board - SMD bullshit - so maybe time to give up.
BUT, there is one weird sympton that id like your guys' help with: even with the bad FETs out of there/the power amp PCB unplugged, when i turn the amp on, my limiter will sometimes glow really bright (like full on short bright) for a split second when i turn it on. it blew a 3A slow blow fuse (with the power amp/shorted FETs out of circuit) once, even. it does not do this every time. sometimes i turn it on and i get a normal dull bulb for a second that gets even duller after the initial switching on. but, like i said, SOMETIMES the bulb will light like there's a short but just for a second.
what's going on here? something is causing the current to spike but only sometimes and just for a second.........any thoughts?? bad rectifiers? bad filter caps? so hard to tell because otherwise it works! voltages/ripples,etc look fine!!
hmmmm