Hi All,
I'm in the process of trying (!) to repair and not having much luck, i replaced the obviously problematic parts (they had definately been overheated, despite the fact that the resistor near Q62 (obviously burnt) is obviously burnt, it still functions perfectly.... After replacing the transistors (Q62 and it's partner right behind it), they stopped getting massively hot on turn on, however Q61 (top blue circle in second pic - also replaced this pair...) (and partner, they are the same transistor powered as a pair...) is still getting massively hot, i mean, in the first ~10 sec of running they will be at 60deg already! The resistor that's giving it "power" is right above the burnt one, it's not dropping the voltage much at all it's about 150ohm from memory and is feeding about 42 or so into the transitors... They get hot quick - one thing - they run as a pair - normally MPSW42 - i replaced them with MPSA42 - because that's what i've got lying around - they have a combined capacity of about 1.2-1.3w - however mpsw about 2w, but to me this doesn't account for the massive heat in such a short short time. The circled diode in the second pic was faulty, short circuit. It's been replaced.
I've checked what i can (there is a missing capacitor, i had a problem desoldering it, so am getting a replacement, i suspected it had shorted out! not so
)
So where i'm at is - amp function -
on turn on it has a ~4.5 amp (limit of my p/s) drain for about 5 seconds (always about the same time, regardless of how many times i've off/on'ed it), after about 5 seconds it goes back to about 900ma drain, which is acceptable, but then the "de thump/protection" circuit cuts out (amp's "started" so it lets audio out) and it goes "thump" through the speaker and then protects, then does it again about 5 seconds later again (protection cutting back out again)... and so forth... The outputs (i've measured) appear to be OK - not shorted and no odd readings i can see....
What happend: user had it in the car and turned a corner and it blew 60 amp worth of fuses... Which would indicate something shorted.. but no go, nothing shorted, if i don't connect a speaker it doesn't produce a "thump" in the power drain at all.....
ANY help anyone can offer me? Sorry the images are big, but i can downsize if some prefer but i am much appreciative of ANY help i can get here!!
http://www.behavingbadly.net/diy/ampsmr.jpg
http://www.behavingbadly.net/diy/ampsmq.jpg
Thanks
Aaron
P.S. Amp is an MTX500D (65v rails!)
I'm in the process of trying (!) to repair and not having much luck, i replaced the obviously problematic parts (they had definately been overheated, despite the fact that the resistor near Q62 (obviously burnt) is obviously burnt, it still functions perfectly.... After replacing the transistors (Q62 and it's partner right behind it), they stopped getting massively hot on turn on, however Q61 (top blue circle in second pic - also replaced this pair...) (and partner, they are the same transistor powered as a pair...) is still getting massively hot, i mean, in the first ~10 sec of running they will be at 60deg already! The resistor that's giving it "power" is right above the burnt one, it's not dropping the voltage much at all it's about 150ohm from memory and is feeding about 42 or so into the transitors... They get hot quick - one thing - they run as a pair - normally MPSW42 - i replaced them with MPSA42 - because that's what i've got lying around - they have a combined capacity of about 1.2-1.3w - however mpsw about 2w, but to me this doesn't account for the massive heat in such a short short time. The circled diode in the second pic was faulty, short circuit. It's been replaced.
I've checked what i can (there is a missing capacitor, i had a problem desoldering it, so am getting a replacement, i suspected it had shorted out! not so
So where i'm at is - amp function -
on turn on it has a ~4.5 amp (limit of my p/s) drain for about 5 seconds (always about the same time, regardless of how many times i've off/on'ed it), after about 5 seconds it goes back to about 900ma drain, which is acceptable, but then the "de thump/protection" circuit cuts out (amp's "started" so it lets audio out) and it goes "thump" through the speaker and then protects, then does it again about 5 seconds later again (protection cutting back out again)... and so forth... The outputs (i've measured) appear to be OK - not shorted and no odd readings i can see....
What happend: user had it in the car and turned a corner and it blew 60 amp worth of fuses... Which would indicate something shorted.. but no go, nothing shorted, if i don't connect a speaker it doesn't produce a "thump" in the power drain at all.....
ANY help anyone can offer me? Sorry the images are big, but i can downsize if some prefer but i am much appreciative of ANY help i can get here!!
http://www.behavingbadly.net/diy/ampsmr.jpg
http://www.behavingbadly.net/diy/ampsmq.jpg
Thanks
Aaron
P.S. Amp is an MTX500D (65v rails!)