Yamahaha RX-V679 DC PRT High

[peterwheat]

Hey all,

I have a Yamaha RX-V679 that is entering protection mode after a few seconds of turning on. Shows "DC PRT 77H" error when I disable the auto protection.

All speaker terminals read ~0.4 volts across, except for the surrounds, which read 0 volts for right and ~0.9 volts on the left, which increases until the receiver kicks off. I'm thinking this is my problem child.

I took it apart and started testing the main output transistors, and didn't see anything blown open (I did this without desoldering, however I compared to nextdoor channel and all were very similar). The attached picture shows the transistors. Attached picture shows them.

Question is, what is my next step for testing?

Thank you for your help!

Service manual is located here, too big to attach

https://drive.google.com/file/d/1VtI...ew?usp=sharing

[petehall347]

most likely the differential transistors . is there no dc offset adjusters ?

[peterwheat]

Which ones are those?

Not that I am aware of, but frankly I'm not that knowledgeable on receiver electronics.

[petehall347]

have you got a schematic ?

[peterwheat]

Update:

I put things back together so I could reverify some voltages. I checked all the active speaker terminals for voltage again, and everything that's active is reading about 400 mV, with close to 0 on the non active channels. I had a speaker hooked up to one of them, and it sounded very distorted unless it was at a whisper like loudness.

[peterwheat]

Originally Posted by petehall347

have you got a schematic ?

Schematic should be in the service manual above, I can attach the main board pdf possibly?

[petehall347]

need to check the power supply first . if thats wrong it will never work properly

[peterwheat]

Originally Posted by petehall347

need to check the power supply first . if thats wrong it will never work properly

Should I just be checking voltages coming out of the power supply then?

[petehall347]

yes check those first .

[peterwheat]

Originally Posted by petehall347

yes check those first .

Checked these voltages, all correct. (within 5% or so)

[petehall347]

look for the -12.4v rail .

[peterwheat]

On the main board, correct?

[petehall347]

yes .if you look at the input to the amps on the schematic its there .

[petehall347]

also measure at for example Q1002 base .should be 0v ..i ask this because offsets are high when active . might be stray voltage getting in here .
i have a feeling the fault might be the input switching chips .
lets see those voltages first though before i get carried away too much .

[peterwheat]

Reads at -12.2V

[peterwheat]

Originally Posted by petehall347

also measure at for example Q1002 base .should be 0v ..i ask this because offsets are high when active . might be stray voltage getting in here .
i have a feeling the fault might be the input switching chips .
lets see those voltages first though before i get carried away too much .

Q1002 is in a Y shape, from the bottom of main board

-0.45V 0V

56.58V

[petehall347]

what does it measure when that channel inactive ? like not selected .

[budm]

Originally Posted by peterwheat

Hey all,

I have a Yamaha RX-V679 that is entering protection mode after a few seconds of turning on. Shows "DC PRT 77H" error when I disable the auto protection.

All speaker terminals read ~0.4 volts across, except for the surrounds, which read 0 volts for right and ~0.9 volts on the left, which increases until the receiver kicks off. I'm thinking this is my problem child.

I took it apart and started testing the main output transistors, and didn't see anything blown open (I did this without desoldering, however I compared to nextdoor channel and all were very similar). The attached picture shows the transistors. Attached picture shows them.

Question is, what is my next step for testing?

Thank you for your help!

Service manual is located here, too big to attach

https://drive.google.com/file/d/1VtI...ew?usp=sharing

So the Surround Left is the only one that has output offset that goes too high after a while then the receiver goes into output high DC shut down?

Is it Surround Left? Or is it Surround Back Left? I ask because you were asked to check Q1002 which is for Surround Back Left, not Surround Left. Please Clarify as to which Left channel is bad.

Below is for Surround Left checking:
Once it goes into shutdown,what DCV do you get on jumper J245 (close to Surround Left output inductor L6, see service manual PDF page 118)?
Is it Positive or Negative Voltage reading with ref to GND?

[petehall347]

i only used Q1002 as an example .. its fairly straightforward looking at the schematic .
from what i read offsets are only high when channel is active . and not just one channel . 400mv offset .
i haven't studied whether it cuts the speaker off or mutes the input when not selected .

[peterwheat]

SR: 0.353
SL: 0.302
C: 0.300
FR: 0.358
FL: 0.305
SBR: -0.009
SBL: 0.814

Those measurements are with all channels selected.

waiting on it to kick off so I can measure the jumper now.