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-   -   yamaha dsp a1000 swiching on and off (http://www.diyaudio.com/forums/solid-state/120284-yamaha-dsp-a1000-swiching-off.html)

homertooties 28th March 2008 10:28 AM

yamaha dsp a1000 swiching on and off
 
Hello everyone well its been a while hope your all good....

I am in process of trying to fix a yamaha dsp a1000,bought it faulty
for ten pounds gonna try and fix it or strip for parts....

Here is the problem ...you switch amp on 2 seconds later switches off again,desoldered all output stages ,desoldered -and + rails supplying power amps no difference,there are five amplifiers ...front,back,centre
are the high pow ,and the rear channels are lower powered ones

Checked output transistors predrivers changed the 22000uf psu caps
no difference doubt its the transformer as it is huge,seems to me it is a psu problem...

Does anyone have a service manual they could mail me or any advice would be fantastic...also checked the impedance switch and cleaned it....

Brouilly 28th May 2012 08:59 PM

Old thread revival.

I just had one of these come into the workshop, not overly confident with SS amps of this size, especially with all the DSP getting in the way - but it is showing the same problem you have here. Did you get anywhere with it?

Amp turns on for a half a second, then switches off. Few seconds later the relay at the mains inlet switches back.

In that second the transistors are seeing voltage from the power supply, they don;t seem shorted.

Does any one have any tips? I may just tell the guy to sell it for parts or send it to someone that knows more. But i'm up for a bit of fault finding.

Cheers

Charlie

tauro0221 28th May 2012 09:15 PM

Hi,
Here it is a link for the schematic.
http://www.sportsbil.com/yamaha/DSP-A1000.pdf

Brouilly 28th May 2012 09:27 PM

Thanks, I found a schematic but was hoping the might be a tell tale answer to such a problem. Seems to be the same issue the OP had.

Just looking over the schematic now, there is so much DSP in this thing!

tauro0221 28th May 2012 10:18 PM

Hi,
I think there it is a micro that check the voltages to be within specs. and if not it will shutdown the amplifier. That it is a complicated amplifier to troubleshoot. The first thing to do it is check the power supplies voltages to see if they are OKAY.

Brouilly 28th May 2012 11:08 PM

Certainly is a complicated amp. On power up the transistors see about 50v before the amp powers down again, so it seems to be working. I noticed in this thread http://www.diyaudio.com/forums/solid...dsp-a2070.html that there is a cap in question that may be faulty. It will be interesting to see how that pans out.

If i had the time it would be interesting to troubleshoot in detail, but I am not confident with the DSP and ICs in the amp to start pulling things apart.

Thanks for your help

Charlie

jitter 1st June 2012 07:02 PM

According to the manual (page 11), "abnormality detection" doesn't take place during the first 3-4 seconds after power on. You write that the amp already turns off in half a second which may indicate that something else is faulty.
See if you can measure points 1-5 on the same page in the short time it's switched on.

The cap in the other thread you linked to is meant to keep the settings stored in volatile memory. When these caps go bad over time, the settings in the memory will not be kept alive for very long and, when erased, the amp probably starts in default mode. Perhaps it is related to what your amp is experiencing, perhaps not, but it is worth checking if it's still OK (in your amp it's C145).
If it's somehow wreaking havoc with the 5 V power supply to the microprocessor, no doubt it will not function properly.
Personally, I would temporarily disconnect it from the circuit by desoldering it from the board (you may remove R195 instead if you're comfortable desoldering SMDs, see section D4 of page 43). This will erase any settings stored in the memory but should not affect normal power provided by IC37 which is 5 V measured on (e.g.) pin 4 of IC40 with respect to pin 1 of IC40.
After removal of C145 power up the amp and see if it works OK. If this did not solve your problem, it seems unlikely that the supercap is the culprit.

Also check to see if the supercap has gone leaky. This stuff is corrosive and will eventually eat through copper tracks. It happened to my Pioneer PDR-555RW (common fault in this model). Once a trace has been corroded through, unpredictable behaviour of the microprocessor may be the result.

Brouilly 10th June 2012 11:25 PM

Thank you very much for your detailed reply - I will follow your steps and report back.

Charlie

Brouilly 12th June 2012 10:01 PM

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.

Brouilly 12th June 2012 10:13 PM

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.


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