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Old 02-11-2019, 08:49 AM   #1
Dannyx
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Question Pioneer VSX-919AH Phase Control blinking (AMP Overload?)

Good day folks. I found a Pioneer VSX 919 receiver in the trash pile and I thought I'd give it a whirl and try and fix it just to prove that I can and pass the time away....after my colleague gets bored of it, since he usually likes taking stuff from me so he can get all the credit, which he just did >_>

The problem is that the "Phase control" indicator flashes and the amp turns off, which according to the service manual which you can get here (pages 43 and 44 - too large to upload) indicates an "amp overload". The operating principle is shown on page 44. Not entirely sure how it all operates, but basically the base of Q5019 shouldn't get pulled low. If it is, Q5019 becomes conductive, which drives the base of Q5020, which then pulls pin 6 LOW, signaling the fault to the processor (which we assume functional at this point). The full schematic is on page 100. Problem is I can't quite figure out WHY that pin gets pulled low and what causes the issue. Mostly these VSX amps have problems with their DSP chips and I wrote a post about one some time ago, but this one is a bit different and looks like the problem lies in the amp section which might just be doable.

Haven't done any in-depth measurements myself yet and I couldn't find a pinout for the PAC014a amp modules, although I DID manage to find one for a STK442 which according to some chaps is close enough, so I at least know what those pins do. I wonder if removing the modules entirely should cause the amp to stay on. Any ideas how we should proceed ? Cheers and thanks !
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Old 02-11-2019, 11:12 AM   #2
R_J
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Default Re: Pioneer VSX-919AH Phase Control blinking (AMP Overload?)

Check for DC on any of the output pins, one or more of them likely has dc trigering the protection circuit.
It looks like it could also be triggered by Q4921 on the W board (trans 3 assy)
I do see a couple icp-N10 (circuit protector fuses) I would check, IC5401,IC5402
I would also check those IC5005 (fuse links?) and any others that look like them

Last edited by R_J; 02-11-2019 at 11:59 AM..
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Old 02-11-2019, 01:18 PM   #3
Dannyx
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Default Re: Pioneer VSX-919AH Phase Control blinking (AMP Overload?)

Shouldn't DC on the outputs return a different error ? Page 43 says AMP ERR should blink on the display.

Now since XOLERR seems to be the line responsible for the error I'm getting, it should be high under normal conditions and go low when a fault is detected ? XOLERR also appears on page 112 hooked up to transistor Q4921 like you said, whose base is on the fan output. I imagine Q4921 is normally "off" when there is power going to the fan and it turns on when power to the fan is cut, pulling XOLERR to GND again. Disconnecting the fan can't possibly cause it to trigger, at least from what I can see, since power should still be present on the TP1 point corresponding to the base of Q4921...that would've been really stupid

I also see NM for some of the components...not mounted maybe ?

Last edited by Dannyx; 02-11-2019 at 01:29 PM..
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Old 02-11-2019, 03:00 PM   #4
R_J
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Default Re: Pioneer VSX-919AH Phase Control blinking (AMP Overload?)

Check the voltages on Q5019 & Q5020, that should give some indication of what is causing the error. You might be missing a voltage that is causing the circuit to give a false error ie: V+5 or V-12_A
I guess NM is the part is not installed

Last edited by R_J; 02-11-2019 at 03:14 PM..
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