Dead Denon AVR-4520 Reciever - 0.7 Volt on 5V Rail

[ic_guy]

Hello dear eevblog community,

i'm more of a 3.3volt guy and as soon as it comes to more than 120 volts i'm completely lost.

my denon avr 4520 unfortunately died last sunday and since then i've been sitting in front of the circuit diagrams at a loss.

The reciever sits in a cabinet and is cooled by an external fan. This probably broke (not sure when) and this caused a lot of heat in the cabinet. From one moment to the next, the reciever switched itself off when playing music.

I already had a Denon where the TOP256YN was defective. I had another one at home and so I replaced this component first, but unfortunately there was no improvement.

After doing some measuring, I can now say that there is about 0.7 volts on the 5V rail. All fuses are intact and there are apparently no defective components.

Do any of you have any ideas as to what the problem could be?

Schematics : https://www.manualslib.com/manual/1621490/Denon-Avr-4520ci.html
Power supply on page: 146

Many thanks in advance

[m k]

Nasty schematics coloring.

So something is pulling you 5V down or it is missing.
Start going back from the output connector.

U6501 is a feedback, it will tell the primary side how to adjust.
But those last rectifier diodes are more promising suspects.

Low dashed line is a relay.
Without 5V other parts can't get their AC.
So only digital side is present first.

[ic_guy]

Thanks for the answer.

I have now tested all the resistors and diodes. Everything looks good. U6501 also removed and tested, also looks good.

My current guess is DS6518 (KIA2431AP), I have a second Denon with a KIA2431AP, should I swap them?

With last rectifier diodes, you mean D6516 / D6515? When I'm probing them, the Current goes up and up. Is this a normal behavior?

[m k]

Of course you can try another D6518.

D6515 and D6516 are correct.
Before them and over the transformer should be an AC voltage of some sort.
After them should be that 5.2V DC.

If voltage or current is pulsing slowly, like once a second, it means an overload.
There power tries to start, see the over current, stop and start again.

If both sides of diodes are AC voltages then at least one diode is shorted.
That can be very bad.

What resistance you get from between 5.2V and GND?
There are large capacitors, let them unload a moment after power off.
Low value there means a short somewhere.
Is it different if you disconnect N6502 output connector?

[ic_guy]

I'm sitting directly in front of the power supply unit, everything else is disconnected.

I have now removed the D6515 and D6516 and replaced them with one from the other Denon. Same behavior.

D6518 replaced, same behavior

Replaced 6501 for fun, same behavior.

Between v5 and GND it is 3 ohms at the beginning and then quickly goes up to 3.2M ohms.

I don't measure any pulsing, directly after starting it currently jumps to approx. 0.5-0.7v and stays there. Even if I then pull the plug, it stays like this and slowly reduces. So what would speak for some kind of protect mode? If I then measure the input of the transformer, I get around 300V.

Still drives me absolutely crazy, so few components and still no clue what it could be

Thanks for your great help, otherwise I would be completely lost

[David_AVD]

Replace capacitors C6515 and C6519. Check the chain of 1M resistors and their associated traces. I've seen a few with issues around there.

[ic_guy]

C6515 and C6519 replaced, same behavior.

All 1M resistors down the line are good. 

[m k]

From where exactly you measured that 300V?

Earlier you said that current goes up and up, I'm not sure what that means.

Remember that swapping parts has a catch.
If part of bad machine is broken it may have taken something with it and then your good part may also fry.
If that happens then it's possible that putting this newly broken part back to good machine harms it also.

Few voltage measurements,
transformer secondary, that is AC, somewhere between it and those coils before D6515 and 6516,
C6519,
D6522, under U6502 and
R6514, between V and C of U6502.

[ic_guy]

Earlier you said that current goes up and up, I'm not sure what that means.

Not the current, the resitances between v5.2/gnd. Which starts at 3 ohms at the beginning and then quickly goes up to 3.2M ohms.
Edit: Oh, now i know what you mean. Ignore this sentence

• Primary transformer ~330v (On the mainline after the first rectifier, just to check if there is main power)
• Secondary transformer .009v
• C6519 2.21v
• D6522 2.58v
• R6513 Starts at ~2.2v and goes down to 1.91v (in around 5 Seconds)

When i measure U6501, its exactly 0.0v

[m k]

U6502 startup goes so that first C6515 is charged through D pin.
So first the main primary winding is just a resistor, but that's a quite short time, possibly difficult to see with the multimeter.
It's also a live side, so don't use scope if it's not differential.
C pin must reach 5.8V before startup goes further.
At 4.8V auto-restart is activated.

So you must get more voltages to C pin.
Check D6514.
D6522 can also be faulty and have its 39V threshold dropped down.
Check also zener over U6501.
If D6514 is faulty it probably is not the cause, so something else is also or has been faulty.

Do you have an AC voltmeter?
The winding behind D6514 must generate a voltage high enough.

E,
check current limiting pin X also.
Q6501 must be operational and pin X connected to ground through those two resistors.
The higher the resistance the lower the current limit.

[Chris56000]

Hi!

. . .I've been searching all over the diagrams for the +5 V Standby supply, and I fear that Denon haven't shown the entirety of the circuits in that Service Manual, as I can't trace the standby switching forward from any of the microprocessor ICs to the power supplies!

. . .I would next take a look on the A+7 V and A–7 V supplies from the "AUDIO_REG_UNIT 8U-210119-5", as these two power supplies are used by the two fans fitted in the bottom of the chassis enclosure, and these supplies are sensed by the control system to shut the main supplies off if there's no supply available for the fans!

. . .Locate the "AUDIO_REG_UNIT 8U-210119-5" from your layout and assembly diagrams and check the "A±7 V" supplies on connector plug N3902 – if either or both of these supplies are low or missing, make sure fuses F3901 and F3902 are intact, and then carry out component checks on the two series regulator circuits on your "AUDIO REG" board – these are simple symmetrical +/– series emitter follower stabilisers and you should have no difficulty fault–finding them!

. . .If these supplies are OK at pins 1, 2 and 3 of plug N3902, I would spend some time dismantling all the boards and examine them ALL VERY CAREFULLY with an illuminated LED magnifier, paying particular attention to any heatsinked regulator transistors and ICs – you might have a dry–joint somewhere on a transistor, IC or connector plug pin that's deleted a supply path somewhere!

. . .See how you go with the above first, these receivers are worth a lot of money and time spent removing the boards and checking them carefully for obvious faults INDIVIDUALLY for problems might turn something up, there's enough adequate information provided in the S.M. to enable you to dismantle and refit all the individual PCB assemblies without risking any damage you can't easily rectify!

. . .If your receiver has been built with that "lead–free" solder muck, as it almost certainly will be, there could be any number of dry–joints and poor connections on the innumerable panels, which will cause no end of baffling and inexplicable fault symptoms!

Chris Williams

 . .PS! Sorry to be so long replying with fault–finding suggestions, I've been thro' that manual for days trying to find the standby supply source and the switching paths back to the PSU!

 

[ic_guy]

- D6514, 0.5V multimeter probing, looks good.
- On current limiting pin X  I measure 245v
- D6522 My TC1 tester goes only up to ~20-30v , can't test it.
- U6501 is a KIA PROGRAMMABLE PRECISION REFERENCES, i don't know how to probe it. https://datasheetspdf.com/pdf-file/952261/KEC/KIA2431AP/1
- Q6501 gets 220v and pulls X to Ground.

Do you have an AC voltmeter?
The winding behind D6514 must generate a voltage high enough.

Yes, but don't know if I'm doing it right.
Measured between 1 and 6 = Shot peak (but my multimeter is slow) above 1V, and then goes down to 0
Measured between 6 and 5 = 0v

[m k]

Manual indicates that current limit pin X voltage must be low, much less than 2V.
Check its connecting resistors and their traces.
You can do that by checking voltages point by point from ground.

Standby power.
Power supply connector's MAINPOWER_MO comes from U2001 (180/281), but it's a 3.3V chip.
Its M3.3V goes to Reset/Supply page 179/281 and beside it goes D5V.
There in the middle of those voltage selectors is D5.2V driven U1904 voltage something disabling M3.3V enabled MAIN_RESET.
Top right of 178/281 has a power supply connector with its D5.2V and a bit lower the same through some coils and renamed to D5V.
Same page and small connector in the center has REMOTE3.3V and B/P_IRIN, they go to page 148/281.
There B/P_IRIN is U6801 something and left of FLD_UNIT is ON/STANDBY switch.
So M3.3V is the standby power.
Maybe chips are hibernating, maybe not.

[Chris56000]

. . .I honestly think the OP is barking up the wrong tree with this – I explained in my first post that I think that main power supply is not being enabled from elsewhere rather than having an actual fault on it – I have spend many years repairing industrials, monitors using switch–mode power supplies of all types, and when they're only producing 0.5 to 1 V out it almost always means they need a turn–on/enable signal from elsewhere!

. . .A power supply that is faulty nearly always produces negligible or zero o/p voltage, or else they trip, or sometimes low voltages due to dried–out output filter electrolytics!

I really do think the OP needs to be looking at what I advised previously – I have found from 40 years experience that if you can't find an obvious fault where you think it may be, you're almost certainly looking in the wrong part of the circuit for it!

Chris Williams

[ic_guy]

@MK: I was wrong, X is 75mV.

@Chris56000
Hi, thanks for your long answer. I also assumed this at the beginning. But the SMPS board should generate 5v even without connection to the rest, as long as you trust the SM (P. 103) :

Is a DC 5V voltage output
when the cord supplying the
power from the SMPS B'D
to the HDMI B'D (1808) is
unplugged?

-> IF NOT, troubleshooting SMPS.

[Chris56000]

. . .You can't always rely on Chinese (and many other manufacturer's!) Fault–Finding Flow Charts I'm afraid – I found a lot of them to be simplified to such an extent that many causes of the breakdown are glossed over or omitted !

. . .A lot of switch–mode power supplies can turn off under overload/short–circuit conditions in far less time it takes a microprocessor system to reset and initialize, so you need to try and beat it at it's own game, which you can do using an external/lab bench type PSU as explained below!

. . .If you have a lab bench supply, set it to +5.6 V, and connect it's negative o/p to the chassis–earth (0V) of your Denon, and it's positive output to the + 5V rail via a 1N5401 diode, with the marked (Cathode) end to the Denon's +5 V rail.

. . .Turn the current limit to zero (minimum), plug your receiver into the mains, switch it on, and then gradually increase the current limit control on the psu from minimum, watching the front panel display and LED indicators for signs of life as you do so!

If the lab psu shows signs of current–limit and you can't reach 5 V output, there could be a short circuit across the line which could be almost anywhere, but you can lift things of the 5 V line in turn by disconnecting plugs/PCBs one at a time, if the lab psu output comes up to 5 V with a large drop in current on the psu Current Meter when a connection/PCB is removed, your fault can only be on the last item you disconnected, you can then refer to the circuit diagram for that part!

. . .If the 5 V line comes up on an external bench supply, even if you still have a "dead" display, or some sort of error code/fault indication, you can then make voltage checks on the many i.c. regulators that are operated off the 5 V  line!

. . .Remember also, if you try this and the front display shows something that suggests part of the system isn't operating, it doesn't necessarily mean that subsection has failed – it might be missing a separate power supply of its own!

. . .If, on the other hand, the entire unit comes to life with a normal front–panel display and your audio returns to normal, you can then see if the Denon's own supply is producing its own power – if it's still at 0.7 V, then it might not have been enabled as a result of your fault condition – however, if BOTH the Denon's internal supply and the lab supply power up together when you feed 5 V externally, something external to the Denon PSU has turned it on @ the same time as you connected the external source, in the event of that happening, I'll give you some further pointers, but we need to try and get the system operating on a temporary supply, as there could be one thing "chasing the other" as it were!

. . .As I commented previously, this unit needs a great deal of time and very careful investigation if you're going to get anywhere, and I have detailed previously and at the beginning of this post the way to go about it and what to look for!

Chris Williams

[m k]

- D6514, 0.5V multimeter probing, looks good.
- On current limiting pin X  I measure 245v
- D6522 My TC1 tester goes only up to ~20-30v , can't test it.
- U6501 is a KIA PROGRAMMABLE PRECISION REFERENCES, i don't know how to probe it. https://datasheetspdf.com/pdf-file/952261/KEC/KIA2431AP/1
- Q6501 gets 220v and pulls X to Ground.

Do you have an AC voltmeter?
The winding behind D6514 must generate a voltage high enough.

Yes, but don't know if I'm doing it right.
Measured between 1 and 6 = Shot peak (but my multimeter is slow) above 1V, and then goes down to 0
Measured between 6 and 5 = 0v

Seems that you better measure away from the transformer to be sure, Like red and D6513.

AC voltages are measured just like DC voltages, like between red and green.
Nowadays meter probes are also keeping their places, older meters may have different jacks for different things.
There probe polarities have no meaning either.

So main transformer's secondary and its AC voltage between red and green before those coils, any red contact point there will do.
Put your meter to AC range and measure, what you get?
You must get something or it can't be the source for 0.7V of the other side of those rectifier diodes, earlier measurement is not enough.

Then main transformer's primary side.
You've already measured over 300V DC between red and green.
What AC you get from between U6502 D pin and green?
All contact points are not the same, don't use frame ground.

Now switch back to DC range and try again.
If U6502 is still starting you get that same earlier 300V DC.
Then the chip should also be loading the C pin capacitor C6515, and finally get it over the earlier measured 2V and some.

You said earlier that voltage over R6513 changes a bit after few seconds.
You shouldn't have that resistor if your machine is for Europe.

You've also said that U6501 was 0V, that shouldn't be so yet.
I'm assuming here that you meant the transistor side of U6501.

You can test those primary side diodes by removing U6501 and using diode test range of your meter.
Those are off line measurements, also some time after a power off, so that capacitors have time to discharge.
There you see a threshold voltage over the measured diode.
You can't see the zener voltage, but you know if the diode is shorted or possibly open.
If D6514 is open you can replace it with D6509, that's from a protection circuit and C6519 will eat the initial bump.
Your earlier 0.5V over D6514, if that was a live situation you may have measured C6519 and a primary side winding.

Transistor side of U6501 can also be tested using that diode test range, it shouldn't conduct.
If it does there must be a protection diode or it is broken.

Using alternative 5V source through a diode is not a bad idea either.
You may even have an easy connection point in that open N6503 connector.

Generally many things are marked open without any other info.
Then others have more info, like that R6514.
Over U6501 transistor you have a zener, what part number it has?
Same with main voltage detection circuit on low left, what capacitors you have?
Then the output side, are your connections like in schematics or something else?

[ic_guy]

@Chris: , then for the explanation, I have connected the HDMIBoard and then get a flashing red led with 5V. So everything looks good for now.

I have now got my hands on a Denon x2400, which has more or less an identical SMPS board. Here I was able to confirm that the power supply generates 5.2V directly when connected without an adapter or additional board connection

@MK, ok will start now.

[ic_guy]

What AC you get from between U6502 D pin and green?

Remember my multimeter is not really fast. But it is at least over 1V for 0.3 seconds, then drops to 0v.
I guess this is the moment where the secondary part gets some voltage and loads the caps. Which are the 0.5v-0.7v I can measure (Which will drop after that)

Now switch back to DC range and try again.
If U6502 is still starting you get that same earlier 300V DC.

Is constantly at 321v. (D Pin - green)

You said earlier that voltage over R6513 changes a bit after few seconds.
You shouldn't have that resistor if your machine is for Europe.

You are absolute right, I guess doing this with Covid19 does not really help

You've also said that U6501 was 0V, that shouldn't be so yet.
I'm assuming here that you meant the transistor side of U6501.

No, measured between Anode/Cathode of the diode side. At start is over 0v and then instant down to 0v.

I will test more later. Thank you so much for the help!

[ic_guy]

Generally many things are marked open without any other info.
Then others have more info, like that R6514.
Over U6501 transistor you have a zener, what part number it has?
Same with main voltage detection circuit on low left, what capacitors you have?
Then the output side, are your connections like in schematics or something else?

I have the europe one, everything which is marked open in the schematic is open on my board.

I placed some parts from the AVR-4520 into the x2400, and all working. (U6501, D6516, D6515, D6518)

[m k]

The switcher can be in an on going OFF phase of remote ON/OFF.
But even then it will charge and let drop the C pin.

So can't say what happened.
The manual is warning about noise and V pin, but that is against switching currents.

You may have done something unknowingly and it may come back.
On the other hand, using hot air may have melted some bad joints.

For the future,
connecting U6502 V and X to S will turn them off,
F to S give switching frequency of 132kHz, F to C and frequency is 66kHz.
So 3 pin operation is possible.