VSX-1021-k MCACC flashing

[Plane Nuts]

Hello All,

I have a VSX-1021-K Pioneer Amplifier that has me stumped. Has MCACC light flashing meaning it is in DC protect mode and will not get out with release mode.
Attached are all the readings I pulled up to narrow down the issue to FR speaker and SBR speaker. I compared resistance values between components in the overload detection circuit of SBR and SBL looking for a short or different values with no luck. note I did not remove any components as nothing stood out of the ordinary.
I have also checked all transistors along the bottom of the amp including Q404 and Q410 equivalents for shorts or opens with no issues.

Not sure what direction to go now, should I remove Q404 and/or Q410 equivalent and test that way to try and confirm issue is 'up stream' from there?

service manual can be found here: https://elektrotanya.com/pioneer_vsx.../download.html

[lotas]

1 Switch the receiver into standby.
2 While holding down the ADVANCED SURROUND button, press and hold the STANDBY/ON button for about three
seconds.

[Plane Nuts]

Hi Lotas,

thanks for the reply however to clarify unit is stuck in DC protect mode and when trying to release it after about 5 seconds it will return to DC protect mode. What will forcing the unit in standby mode do? is it not the same as release mode (tune down and multi-zone on/off)?

[Plane Nuts]

contiued looking to find issue and not getting anywhere, and help?

[budwich]

I think you need to try what lotas suggested.... to see if resetting helps.

Since you have some good channels (how did you determine which were bad? OK... I see from your attachment that there is 12v on those detection lines), with disconnected power, do some impedance tests at "strategic points" and compare those between the suspect channels and good ones to see if it helps point to areas.

Look at the possible dc paths in page 53 (example).... checking caps along the signal route as a start and then active devices there after.

why 12v? what are the operating voltages (rails?) of the amp section?

[redwire]

Your 12V readings at R678 (SBR), R462 (FR), that looks like two channels have a blown power amp. This causes XDCERR to go low 0V and the MCU goes into protect mode.

When an AV receiver is stuck in protect mode, a quick test is measuring the output voltage of EVERY channel (not at the loudspeaker terminals cuz the prot relays are off) but at the bias-set testpoints like TP402, TP407 etc. Must be under around 1V. Not 12V!

I think I got a different service manual here: https://elektrotanya.com/pioneer_vsx.../download.html

[Plane Nuts]

thank you all for the input, I tried what lotas suggested and nothing happens.
now to check for impedance tests at 'strategic points' any suggestions on where to start? I have been concentrating to the right of Q476 and Q482 should I bee looking on the left? Finally @redwire what do you consider the power amp? is it what is within the red square on page 56?

[budwich]

"strategic points"... :-) my view is where the easiest access and identifiable points on the board. I am thinking on page 78-79 shows 12v sources and op amps. Not sure how accessible things but some points that are easy between r/l/sb might point at something.... not that I am good at reading schematics... :-) I was looking where 12v could show up along a signal route.... that's where I got to.


ADDED... never mind about the 78/79, i think those are preamp outputs.

[Plane Nuts]

Over the weekend I did some testing and metering, and attached is what I have come up with. Note when I mention swapped I swapped with between this channel and SBL. my next step would be to remove and test C501 and or C574 however these are surface mount, a little more tedious. I assume this is close to the problem due to the weird readings at Q480 due to the spike with reading. Anyone see something that I am missing? or something else to check?

Also note the main problem is that the 4.8V on the Right side of the drawing should not be there this should be 0V

[budwich]

not sure if it is an "record keeping" error or your measurement is "funny". I don't think the high voltage rails which you show as (-58v) is correct. One should be positive in some form... I think. Please confirm.

Based on a quick read of the schematic, the top rail should be +58v.

One additional thing... you mentioned the 4.8v on the output in this latest "test"....BUT didn't you previously indicate 12v.... what changed?

[Plane Nuts]

Budwich, the top rail is +58V, and what changed from 12v to 4v is the fact that Q476 and Q482 are now not installed in the circuit(removed) . I also forgot to mention Q481 was also swapped.

[budwich]

oops my eyes mistaken the track line for a negative.
good work on trying to isolate things.
I am thinking there is not enough negative to offset the positive. What happens if you put back c519.... that might turn on q484 and bring things down. For that matter, all those devices associated with q484 might go back.

how are you checking components ... with a cap / device checker or just a meter?

[budwich]

it appears that potentially to get q484 to fire, you need to cause Q479 to fire. You might check c508.

[redwire]

I looked at the voltage measurements, they are a bit coarse i.e. rail is shown as -56V but same node is -56.7 or -57V which is backwards.

Q480 is completely off, as it should be- trying to correct the +ve offset voltage. But across R694/R688 there should be no voltage drop i.e. between speaker output and Q480-B, not 1.8V measured. So the measurements are messy or C506 or Q480 is leaky.
Q484 doesn't appear to be doing enough. Either Q479 is lazy, the collector voltage is staying low at -56.7V or Q484 is lazy.

Keep checking transistors and make sure the p/n and pinout are correct.

[Plane Nuts]

Thank-you budwich and redwire for the inputs, I am checking components with a voltmeter, and including caps in the cap setting removed from the circuit, If I am unable to get a reading as I might be out of range I will swap it with the left channel. I will also compare with the left channel. regarding the coarse readings I will go back and double check, some for sure have variable values so I am giving you a mid range as it does not have time to stabilize in the in the 5 seconds it is in release mode. I will check out the other items when I get time later tonight or tomorrow.

[budwich]

caps are pretty hard to check with meter (my finding). Your swap technique is good.

from limited experience (crown amp and onkyo receiver), when I see voltage on one side that looks close to the "rail", it is likely that component is not conducting. IF it was, there would potentially be a voltage drop across the one watt resistor and would make the voltage there after lower. Of course, I am more than guessing... :-)

I would put back some of the components as suggested and see what the result. I am not sure that i see how you got to the "4,v" level and which components contributed the reduction of DC.

[Plane Nuts]

Redwire, see attached i have taken the values again and updated the drawing, note all the lower values (below 10v) are all variate about 1 or 2 volts and that is a rough middle point I entered. Example the 4.8V reading starts at 5.9 and goes down to 4.4v before going into protect mode again (this is over a 5 second period) the 0.6V and 0v at Q473 and Q479 at stable.

[budwich]

not sure why you tried comparing a good channel reading wth a bad channel reading around q484. The might help point you further towards the input side versus the output side.

[budwich]

another thing measure voltage between zener and diode (pairs) and compare those to a working channel.... maybe a zener isn't working.

[redwire]

Those numbers are better, I would say Q484 is weak or the new Q480 has a problem - wrong pinout or part.