I bought an AB 600 LX (Class AB) and AB9620B (Class G) on an auction site. They apparently came from the same person, whether a DJ amp rental or maybe a band, etc. from California. Both had issues.
Anyways, sent the 9620 to Bob at AB Amps and he had it fixed in no time, and sent me a new VU board with brand new volume pots. So that amp is good to go as soon as it's put back together, which will be soon as I'm working on something else at the moment.
The 600LX is another story though. While the 9620 would power up, then go straight into protection mode, was able to disconnect a channel board at a time to discover one of the boards was bad. The 600LX however powers up, but doesn't seem to go into protection, and it's fan isn't turning on. Amp is fairly basic with not a lot going on, minimal caps, etc. Thinking it's something simple, and seeing as ON SEMI parts are inexpensive, was planning on putting in new transistors, and also going the slow route of probing until something doesn't jive. There IS a schematic, but it's a poor transfer to .pdf and Bob doesn't have anything better and doesn't really work on them, so kinda stuck doing things the hard way. Was just wondering if someone was really familiar with these and could give some pointers on what to check 1st. DC Offset is rather high at like +1.6v, so something is goofy. Fuse isn't blown. Dunno if something is actually bad, or if a dead fan puts it in some sort of "off" state, though the offset being high like is probably something died. Any input this amp would be greatly appreciated.
Anyways, sent the 9620 to Bob at AB Amps and he had it fixed in no time, and sent me a new VU board with brand new volume pots. So that amp is good to go as soon as it's put back together, which will be soon as I'm working on something else at the moment.
The 600LX is another story though. While the 9620 would power up, then go straight into protection mode, was able to disconnect a channel board at a time to discover one of the boards was bad. The 600LX however powers up, but doesn't seem to go into protection, and it's fan isn't turning on. Amp is fairly basic with not a lot going on, minimal caps, etc. Thinking it's something simple, and seeing as ON SEMI parts are inexpensive, was planning on putting in new transistors, and also going the slow route of probing until something doesn't jive. There IS a schematic, but it's a poor transfer to .pdf and Bob doesn't have anything better and doesn't really work on them, so kinda stuck doing things the hard way. Was just wondering if someone was really familiar with these and could give some pointers on what to check 1st. DC Offset is rather high at like +1.6v, so something is goofy. Fuse isn't blown. Dunno if something is actually bad, or if a dead fan puts it in some sort of "off" state, though the offset being high like is probably something died. Any input this amp would be greatly appreciated.
Anyone familiar with AB Amps? Was hoping to get some insight from people that might have experience working on their Class AB amplifiers from the 90's.
It's not overly crowded and not a lot there (mainly resistors). Was hoping someone could give some pointers on what to test 1st to narrow down where the fault might be, or if/when these things fail, is there a general culprit?
It's not overly crowded and not a lot there (mainly resistors). Was hoping someone could give some pointers on what to test 1st to narrow down where the fault might be, or if/when these things fail, is there a general culprit?
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