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Old 12th June 2012, 09:35 PM   #11
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Now that the amplifier stay on check the voltages with the voltmeter with the voltage selector in AC. Read the voltages and if they are good they should read almost zero. Caution when reading DC voltage in AC it is take a while to settle. This will tell you if you have ripples in the power supplies voltages.
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Old 12th June 2012, 09:40 PM   #12
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Thanks.

I think i'll lug it into work and take a look. Surprised that it just started working, I was wondering where to look next!

Think i'll stick to valves when I can
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Old 13th June 2012, 01:04 AM   #13
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Hi,
I check the schematic for the PRT and when you have time check pin 17 to IC40. It should read zero volts. If it read 2 volts or higher means the PRT circuit it is not working right. It is triggering the shut down.
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Old 13th June 2012, 07:12 AM   #14
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Quote:
Originally Posted by CSlee View Post
Unfortunately it wasn't the supercap. I removed it and the amp still turns on for a moment then dies. However, without the cap the dial movement is random compared to before.

Will check that B+, 15v and 5v are all OK. But as you said, this check ins't done in the first 3-4 seconds.
The random behaviour is to be expected when the memory gets erased.
Check all voltages anyway and don't rely solely on the fault detection for that. I find that if I assume something can't be the cause of a fault it sometimes is.

Quote:
Originally Posted by CSlee View Post
Update

I replaced the supercap, and no change. But I kept powering up to see if there was any change, and slowly some words popped up on screen. And after about a dozen power ups the amp has now stayed on saying "concert hall A" on screen.

I will leave it on for a while, and see what happens when powering on/off again.
Good idea, it gives the supercap the chance to recharge and gives you the opportunity to check points 1-5 of page 11 of the service manual.
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Old 30th October 2013, 09:21 PM   #15
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Default Bad resistors found

I had the same problem with the A1000 shutting off. The protection circuitry was causing a shutdown as there were several volts of DC output on the center channels speaker output (measured at the speaker terminals) and on the left channel. After days of testing the voltages using the schematic in the service manual, I found that two resistors had blown and were open: R424 and R351. These resistors are near Q337, one of the large transistors mounted on the large heatsink toward the back of the main board. These are 27k resistors.
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