Denon AVR-X4000 – Fast red blinking after 2nd relay

[SevenOFF]

Hi everyone,

I’m working on a Denon AVR-X4000 that goes into protection mode (fast red blinking LED) shortly after the second relay click.

According to the service manual, a fast red blinking LED indicates a DC detection (DC_DET) or ASO (abnormal current) fault, meaning the unit is detecting a potentially dangerous condition on the power amp or power supply side.

Here’s what I’ve done so far:

• Fully opened and cleaned the unit (a lot of dust inside)
• Removed and visually inspected the AMP board → nothing visibly damaged or burned
• Testing is done with nothing connected (no speakers, no HDMI, etc.)
• Only once it powered up normally and worked for around 5 minutes, then went back into protection
• I tried disconnecting the BN704 connector (carries DC_DET, ASO_DET, THERMAL signals from the AMP board) to test if the AMP board was responsible
  → But I’m not sure whether disconnecting BN704 might itself trigger protection, or if it actually isolates the AMP correctly

I’m attaching a short video of the behavior :

https://youtu.be/lzmcI9jLVPY

and also the full service manual in case anyone wants to check the schematics or pinouts

Any ideas are welcome — thanks in advance!

Seven

[CapLeaker]

Look hard on all the connectors on the PA board (with the big heat sink) and check every connector. Maybe it is simple as a wire pulled out of a connector or a bad solder joint.

[SevenOFF]

Hi, already checked the PA board and looks fine and i've disconnected bn704 and it's still doing the red light so i think that the PA Board isn't the issue but not sure
here is a few pics :

edit : i've removed the whole PA Board from the denon and it's still doing that so i don't think the PA Board is the issue lol

[SevenOFF]

okay so small edit, after i unplugged the whole amp board didn't see but it blink red but slower this time sooo i'm lost rn ;-;

https://www.youtube.com/watch?v=yAoLvnDXHI8

2nd edit : i tried to start it after that i've recorded that video, after a few minute plugged in with the red blinking light, i had the power amp disconnected and it worked for a brief amount of time like 10s until a 3rd click happend sooo i'm pretty sure it's either the PSU board or the main board

[CapLeaker]

Why would you start the amp without the PA? The blinking light means you got trouble with the PA. Either it has a short / over current condition, or there is an open or not fed power somewhere on that board.
Download the Service Manual and go through the troubleshooting steps. Start with all the little power supplies and make sure they all there and working to spec.

[SevenOFF]

the issue can be the PA but it can be the PSU board too or the main board no specially the PA from what i've read, i've checked the transistor with a multimeter and it seem fine, and i've tested some small resistor seems okay too giving the right amount

[dobrykamil]

Put the amp board back and attach all cables. Black probe on the chassis, red on any pin of the brown, bias connector. Switch avr on. With working channel, you should have there 2-30mV. Do this for each channel. A rapid flashing LED, means DC protection. If you disconnect amp cables, over current protection will kick in (slow blinking LED). It's a Denon's thing. Once you find faulty channel, let us know, what voltage are you getting on bias connector. If it's positive value, then check KTC3206 transistor, as they quite often fail.