Denon AVR-X1600H repair help

[wwwpro]

Hi all,

I have a Denon AVR-X1600H stopped working recently.

It was originally went into protection mode and complaining about DC power issue. After some troubleshooting steps, and found that both fuses F3001 and F3004 on regulator board were blown (Page 32).
The AVR went out of protection mode after replacing both fuses and boot up normally but no audio output.

I did follow the schematic and confirm most of the power supplied are correct.
On BN823/CN823 I am getting all +5V, +12V and -12V from the regulator board. (page 27 of the SM)

The 5V missing are the following (page 12 of the SM)
D5V_POWER
DV_POWER
DA_POWER
DA_POWER2
CEC_POWER
CEC_POWER2
NET5V_POWER
H5VOUT_POWER

I can only measure 3.3V from the above which I believe it should be 5V instead.

I suspect the MCU (IC751) is not sending out the "mainpower" signal to kick start the 5V circuit on SMPS?

Any suggestion is appreciated.

Here is the service manual.
https://www.manualslib.com/manual/2798515/Denon-Avr-X1600h.html

[MathWizard]

So why did both fuses blow, they must have went at the same time, did you check all around there with it un-powered with a DMM ? Something probably went short or near short circuit, and passed way too much current for the fuses. Maybe it was temperature related, if it doesn't immediately blow up again, after replacing the fuses.

I'd want to un-solder and check all the electrolytic capacitors, at least on the power rails, with a DMM or an LCR/ESR meter if you have one. I'd check all the diodes and BJT's and regulators too. But yeah I know, taking apart a stereo, and desoldering a bunch of stuff isn't for everyone, but taking out the caps, really makes it easier to check the rest of it.

Also I'd want to know for sure what the SMPS is doing, does it share those fuses from that AC in ? What voltage is the AC in ? I'd check all that unpowered at 1st too. If the SMPS isn;t working now, and the fuses aren't blowing, I'd be looking there right away too.


When testing and repairing stuff like this, it's great to use a series limiting light bulb, ...in series with the DUT. Then if the DUT becomes a short for any reason, even like from your DMM probes slipping, welll then all that happens is the old style incandescent light bulb turn's on. But depending on how much current the DUT draws normally, the voltage drop across the bulb can be a lot, and the DUT might not work right.

Also an isolation transformer would be nice, and an auto-transformer.

Do you have an oscilloscope ? The voltage rails might be doing worse things than a DMM can see. And sometimes for repairs like this, I will disconnect certain areas, and power them from my own PSU, with safe current limits.


Ok but you're saying the SMPS is not getting a power-good, turn-on signal ? Again I'd check as much of both PSU's un-powered 1st, then I might try applying the power-on signal, and see what happens. If the SMPS sees that it has a problem, it won't want to turn on, or not for very long, and you might need a scope to see it trying.

For the audio signal, I'd make sure all the chips are getting Vcc and aren't burning up. Then I'd start tracing the signal path in from the inputs. Depending on the PCB's, it might be easy to remove a section, and power it and check it, but again I have a bench PSU, so it's pretty safe.

[wwwpro]

Thank you for your reply @MathWizard!

At the beginning the unit was working for less than 1 mins then shutdown.
I thought the IC305 (KIA7805BPI) is causing the issue (seems common fault for Denon AVR), so I went ahead and replaced the LM7805.
Fuses were gone after the regulator replacement, I swapped the regulator back and replaced those fuses.

The unit went on "protection mode" before and complain about the DC output of the power amplifier is abnormal.
I cleared the protection history and the unit is "working" since than, no more shutdown. I left it running for over 10mins still nothing turning itself off. I can feel the heat sink is heating up(normal temperature), this indicating the power supply to the amplifier is working?

On BN823/CN823 I am getting all +5V, +12V and -12V from the regulator board. (page 27 of the SM)

Unfortunately I only have a DMM with me for troubleshooting, the majority of the SMPS is working(the standby 5.2V on BN601 Pin 1&2 is working) except for the "MAINPOWER" Pin.
My understanding for the "MAINPOWER" is a signal from the MCU (IC751) Pin 139 > L7404 > CN741 Pin6 > back to the SMPS

All the IC VCC seems to be correct.

[wwwpro]

Did a test to supply 5V to SMPS MAIN_Power (BN601 pin6) while the unit is unpowered. I can hear the clicking sound from the relay RY601.

Wonder if I can bridge CN823 pin 5 and CN741 pin6 to fake the power on signal?

[MathWizard]

Yeah it all sounds pretty good. Ok so a low voltage regulator, powered all the time, it blew the fuses. Yeah for that relay and transistor, the MCU must hold that pin high to turn on the relay, to pass power to the SMPS.

Did you check for a broken PCB trace or lifted pad between the 4.7k base resistor, and the MCU ? If that signal really is missing from the MCU, I wonder why.

Just applying 5V to that base resistor divider, from the 5V rail should be fine, or even off the 12V rail, but then I'd probably add a few more k. But when testing that, or in the final version for sure, I'd cut the trace back to the MCU, just in case the voltage is a problem for that pin, for any reason.

Now there might be other pins going to the MCU, telling it there's still a problem tho. Sometimes the problem sensing circuits, can go bad themselves too.

[wwwpro]

Thanks again MathWizard.

Something strange just happened before I bridge the 5V over to the main power pin. The whole front display panel was gone and the power amp is no longer heating up.
Not sure is something short along the circuit board. I found the fuse F1001 is gone. Now I have to wait until the replacement part arrives before I can go ahead the troubleshooting.

Back to the topic of the missing 5v from the MCU main power signal pin. Is it possible the MCU still keeps the last protection error and stop sending the signal out? Although I have followed the service manual to clear the protection history.

[MathWizard]

I didn't look up the protection circuits, but if time is no big deal, I'd disconnect as many PCB's as I could, and check the PSU's with a dummy load like a few power resistors. And for instance the Front display PCB, I'd check it all over unpowered again. That's were F1001 was, then I'd power it or any other troublesome PCB, off my own PSU. You might still need some other voltages from it's PSU, like on my stereo, it's Vacuum Florescent Display uses an AC voltage tap.

I have my main 3CH bench PSU that I can set a current limit on, which is really handy. So I'd hook up 5,12V and then I still might need to turn on a logic circuit, or make some little circuit with a few voltages even. But that's going all out, and I wouldn't make money by the hour. But if you don't have one, you can try using 5 and 12V PSUs from cableboxes/etc. And even just make some voltage divider or basic BJT circuits or regulators on a breadboard, might be enough for some voltage/currents just to turn on and idle a few circuits on a PCB.

My stereo is some used Denon AVR-2802, it had a problem within the 1st day, but I decided to keep it as a project. Now a year later the main MCU is getting worse, and it's not sending volume info to certain chips, some of the times when it should. But it still always updates the dB on the display, so the MCU is receiving the data from the knob and remote. The volume chips also seem to have a problem, and I was already programming my own MCU to help them. Now, I'll have to read the volume data from the VFD, and other places like the IR-sensor and rotary encoders. Today I solder on some wires for all that, and both those last 2 things are new to me.

So I need to decode some more digital signals, and get the volume and input CH info I need, to send to the input CH/vol chips. And 8MHz is not really fast enough, for the ways I'm trying to do it in assembly so far, so I'll try 12MHz.