VSX-74TXVi MCACC Flashing

[MobileXT]

Im working on a AV Pioneer VSX-74TXVi receiver that one day wont turn on with flashing the MCACC. I replaced IC5301 AND IC5302 still the same problem. Any help would be greatly appreciated.

[R_J]

Re: VSX-74TXVi MCACC Flashing

Do you have the service manual? if you do, check page 191. I suspect you have a problem in one of the output sections. Replacing the fault DETECTOR is not fixing the FAULT.
Check the output transistors in each channel, check the dual emitter resistors, and if you can turn on the amp. Check the DC voltage on CN4003~CN4006 These are the output pins and should be at near zero volts

[R_J]

Re: VSX-74TXVi MCACC Flashing

Disregard my previous post.I looked at page 192 and did not realise they were the output transistors. My mistake, I was looking at the heading "DC Detection Circuit"
Were those outputs ic5301 & ic5302 actually shorted? and was R5327 ok? Were R5321 & R5322 ok.

[madan1]

Re: VSX-74TXVi MCACC Flashing

Im working on a AV Pioneer VSX-74TXVi receiver that one day wont turn on with flashing the MCACC. I replaced IC5301 AND IC5302 still the same problem. Any help would be greatly appreciated.

Why did you change those transistors?

[MobileXT]

Re: VSX-74TXVi MCACC Flashing

Disregard my previous post.I looked at page 192 and did not realise they were the output transistors. My mistake, I was looking at the heading "DC Detection Circuit"
Were those outputs ic5301 & ic5302 actually shorted? and was R5327 ok? Were R5321 & R5322 ok.

I will check on those resistors I will update later.

[MobileXT]

Re: VSX-74TXVi MCACC Flashing

Why did you change those transistors?

Thinking that would be the problem but is not.

[MobileXT]

Re: VSX-74TXVi MCACC Flashing

Disregard my previous post.I looked at page 192 and did not realise they were the output transistors. My mistake, I was looking at the heading "DC Detection Circuit"
Were those outputs ic5301 & ic5302 actually shorted? and was R5327 ok? Were R5321 & R5322 ok.

I check with multimeter it was ok IC5301 AND IC5302 but I did replaced it anyway just to make sure but still end up "Amp Error" then shutdown to protection mode.

[madan1]

Re: VSX-74TXVi MCACC Flashing

Thinking that would be the problem but is not.

But did you do any tests? Did you check them for shorts?
Also, If those fail, they blow and the emitter resistors ( as already mentioned above ) and usually the previous stage(s).
Another thing you can do - if you suspect that specific transistors, just remove them. If the previous amp stage is fine, the unit should power up fine.


By the way, that amp has 7 output channels and each of that channels has a pair of output transistors just like those you changed.. I'm not getting how you decided to change exactly that particular pair... what tests did you do to determine that this channel is causing the problem?

[R_J]

Re: VSX-74TXVi MCACC Flashing

What about the outputs in the other (5) channels? [ic5001/5002, ic5101/5102 etc.], did you test them also or just the one channel

Check the DC voltage on CN4003~CN4006 These are the output pins and should be at near zero volts. If one is reading a positive or negative voltage above a couple volts that would be the bad channel

[MobileXT]

Re: VSX-74TXVi MCACC Flashing

But did you do any tests? Did you check them for shorts?
Also, If those fail, they blow and the emitter resistors ( as already mentioned above ) and usually the previous stage(s).
Another thing you can do - if you suspect that specific transistors, just remove them. If the previous amp stage is fine, the unit should power up fine.


By the way, that amp has 7 output channels and each of that channels has a pair of output transistors just like those you changed.. I'm not getting how you decided to change exactly that particular pair... what tests did you do to determine that this channel is causing the problem?

On The other side forum pointed me that could be the cause of the amp error. The unit power on with the combination of advanced surrounds + enter the receiver reset an turn on after initiating 5 to 10 minutes will shutdown with amp error on FL display.

[MobileXT]

Re: VSX-74TXVi MCACC Flashing

What about the outputs in the other (5) channels? [ic5001/5002, ic5101/5102 etc.], did you test them also or just the one channel

Check the DC voltage on CN4003~CN4006 These are the output pins and should be at near zero volts. If one is reading a positive or negative voltage above a couple volts that would be the bad channel

Ok I will look on this one but how to access these test voltage without removing the amp block? Is there any test point outside that can easily access?

[R_J]

Re: VSX-74TXVi MCACC Flashing

Can't you access the X board? Why did you pick the two outputs you did? Why not the other 5 sets of outputs?
You are the one with the amp in front of you, so you would need to at least provide some pictures to see what we are dealing with.

[MobileXT]

Re: VSX-74TXVi MCACC Flashing

Can't you access the X board? Why did you pick the two outputs you did? Why not the other 5 sets of outputs?
You are the one with the amp in front of you, so you would need to at least provide some pictures to see what we are dealing with.

Here is the picture inside the amp block I will upload more pictures later.

[R_J]

Re: VSX-74TXVi MCACC Flashing

You should be able to get to CN4003~CN4006, they are on this board

[MobileXT]

Re: VSX-74TXVi MCACC Flashing

You should be able to get to CN4003~CN4006, they are on this board

On CN4003 I have -.360v on Standby Mode
On CN4006 I have -0.700v on Standby mode

[MobileXT]

Re: VSX-74TXVi MCACC Flashing

Reading from the Amp

White reading = -1.60v
Purple= -.292v
Orange= -.255v
Green = -.279v
Brown= -.267v
gray= -.259v
yellow = -0.083v

[R_J]

Re: VSX-74TXVi MCACC Flashing

The amp must try to turn on, being in standby the voltages WILL be next to 0. See page 191, try doing the release mode. while monitoring one channel output at a time, This should cause the amp to turn on, then shut down with the error but should show which channel has the dc offset fault
The plugs have designations CN400x, and either pin 1 or 2

[MobileXT]

Re: VSX-74TXVi MCACC Flashing

The amp must try to turn on, being in standby the voltages WILL be next to 0. See page 191, try doing the release mode. while monitoring one channel output at a time, This should cause the amp to turn on, then shut down with the error but should show which channel has the dc offset fault
The plugs have designations CN400x, and either pin 1 or 2

I Attached the result of the Diagnostic from Pages 191.

[R_J]

Re: VSX-74TXVi MCACC Flashing

I Attached the result of the Diagnostic from Pages 191.

You have an amp output problem. Do the test I asked so you know which channel has the problem. If you look at page 192, you will see you have about 3 seconds to test for the offset voltage
Or remove the amp section and test every transistor and resistor in ALL the amp outputs
What you need to do is have your meter connected to one of the output points, the turn on the amp (you may need to re-run the diagnostics each time). The amp should turn on for about 3 seconds and then turn off with the error. during this time you should see one of test points voltage go to + or- 5~50 volts. if the voltage is near 0, that channel is ok, the one with voltage is the problem channel

[MobileXT]

Re: VSX-74TXVi MCACC Flashing

You have an amp output problem. Do the test I asked so you know which channel has the problem. If you look at page 192, you will see you have about 3 seconds to test for the offset voltage
Or remove the amp section and test every transistor and resistor in ALL the amp outputs
What you need to do is have your meter connected to one of the output points, the turn on the amp (you may need to re-run the diagnostics each time). The amp should turn on for about 3 seconds and then turn off with the error. during this time you should see one of test points voltage go to + or- 5~50 volts. if the voltage is near 0, that channel is ok, the one with voltage is the problem channel

Thank you very much! I'm kinda understand what you saying now. I will keep you posted once I do the test.