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Old 15th May 2015, 07:39 AM   #1
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Red face Akai AA-V1500 Amplifier Repair Help

After a little help with a repair to my trusty old AA-V1500.

I have had the amplifier for roughly 15 years and it has done me well until this week, when the wife turned it on one day only to find it going into Protect mode. Just the night before it had been working just fine.

Upon disassembly, even with the pre-amp and inputs boards removed still goes into Protect mode. No obvious signs of damage, a little heat discolouration around some heatsinks but nothing else I can see. The power rails I can find (+/- 15V and +/- 50V) both measure OK.

If I bypass the protection circuit and engage the output relays I get +20V at the positive speaker terminals, both left and right channel. This suggests a common fault to all channels yet from what I can tell the power supplies are fine?

If anyone can give some tips or tell me where to find a service manual it would be appreciated, I'd love to breathe some life back into this trusty old amp.

Some pics:

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Cheers,
Jason
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Old 15th May 2015, 10:47 AM   #2
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I cannot find service information or this model listed but as both channels have the same DC on them, check for a bad earth point on the main board. Could be a poor common ground. Is the fault on all channels?
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Old 16th May 2015, 08:43 AM   #3
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I haven't placed it into surround mode on the bench.

I am struggling to find a schematic myself.

I have found that the amp board has two earths; M-GND (main power/speaker ground) and GND (signal ground). I can't see any traces of M-GND going into the amplifier drive sub sections, only GND. There is a high resistance (appears to change when I measure it - capacitor?) between GND and M-GND and I can't seem to find where or how they are coupled on the board.
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Old 17th May 2015, 01:30 AM   #4
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So.

If I bodge the 2 earths together, it clears up the +20V offset on the output terminals, and will play audio. Unfortunately I still have to override Protect mode - seems wherever the protection circuit picks up it's earth from is also damaged.

I really need a schematic!
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Old 21st May 2015, 08:47 AM   #5
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Anybody got any advice or perhaps a source for rare service manuals?
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