Denon AVR-1603 power rail question (B+, B-)

[David_AVD]

The ICP-N15 type devices that look like 2-pin TO-92 transistors are one-shot.

They are not Polyswitch / PTC / resettable devices and usually have a lower resistance than a PTC of the same rating.

I've seen them in plenty of gear dating back to well before polyswitches were common.

[Martin72]

Together with D157, Q117 is a kind of overvoltage protection, the rest is in the hands of the controller.

But, previously, it was said that the power rails were ON, not with the good voltages though.

He did a RESET on the receiver and the relay switched to on, if I remember it correctly.
I strongly guess it will switch off again when the controller detects a (still persisting)failure.
Therefore he should check the protection signal also, imho.

[guizmo1967]

The relais will switch on, when....

...Q116 is conducting...
...Q117 is NOT conducting...
...RLY_POWER signal is high.(CP555, pin13)
Check the state of the PROTECT signal (CP555, pin7)

That's all true ! PROTECT pin is +4.8V

The Q117 drives the Q116 which gives power to main transformer. But, previously, it was said that the power rails were ON, not with the good voltages though.

When exactly the PWR_DOWN comes high? When IC105 goes OFF, you lose the power rails, because the relay RLY106 turns OFF.

What are the voltages on these connectors?

The power rails were on because I forced it to be on with the reset procedure I described !

The only voltage I get on these connectors is CPU_5.6V (+5.6V) because the main relay (RLY106) is not on .... but if you want I can force it and tell you the rest of the voltages !

When I do a RESET, all voltages stays on forever, the CPU don't shut down nothing ??

[guizmo1967]

One more thought, maybe the main CPU is dead but I check what turns on the standby led and it's a 16 pins IC (BU2090F) that DATA and CLK are driven by the main CPU, so it is not dead

[guizmo1967]

Ok for all following this problem, I did RESET the receiver to turn on RLY106 and those are the voltages I got:

CP555
1- +16.48
2- -8.26
3- -8.26
4- -33.8
5- 0
6- 0
7- +0.56
8- -7.31
9- 0
10- 0
11- 0
12- 0
13- +4.66

CP556
1- +5.54
2- 0
3- -8.26
4- -8.26
5- -23.5
6- +6.64
7- 0
8- 0
9- +4.94
10- +4.95
11- +49V

There is an error on the schematic for CP555 pin 1, on the board it is +24V

All reference to anode of D153 !!

!!!!! THERE IS something wrong with GROUND !!!!! If you add +8.26 to all the voltages that are not right, then they will be OK

[Audiorepair]

All reference to anode of D153 !!

!!!!! THERE IS something wrong with GROUND !!!!! If you add +8.26 to all the voltages that are not right, then they will be OK

Yes, likely you have a fried ground trace(s) when you shorted the transistor to heatsink.
This ground is the one that goes to the 15 volt regulators' ground, which should be chassis ground, which is not the same ground as your Star ground reference.

Also the schematics show pins 1 & 3 of CP555 as connected together, where your readings show otherwise. 
Perhaps this trace is fried (also).

[guizmo1967]

how can I found a fried ground when there is no burn trace anywhere ?? What's your technique ??

[Thunderer]

Those voltages are so off.

It is the time for resoldering. You may have a or some cold solder joints. Look for soldering joints that seem interrupted (I want to say "fissurés") and reheat them. Be generous with  the solder. Check with a ohmeter if you have ground, rails continuity.

Start with power connections.

[Audiorepair]

how can I found a fried ground when there is no burn trace anywhere ?? What's your technique ??

Pins 1&3 of CP555 and pins 3 & 4 of CP556 should all be connected to chassis ground.
The 15v regulator grounds should also be connected to chassis ground, there is a ground trace from the regulators up to CP555 and CP556 which needs to be intact.

Check this with a multimeter in ohms mode with the unit turned off.

[guizmo1967]

Pins 1&3 of CP555 and pins 3 & 4 of CP556 should all be connected to chassis ground.
The 15v regulator grounds should also be connected to chassis ground, there is a ground trace from the regulators up to CP555 and CP556 which needs to be intact.

Check this with a multimeter in ohms mode with the unit turned off.

They all have good continuity to chassis ground !

Those voltages are so off.

They are not, If I use the right ground reference for each voltage I need to measure, they are spot on, even B+ and B- that were so off before.

I use these as ground reference, anode of D153, chassis ground (any screws on the board) and pin 2 of CP104.

Let's say I want to measure:
B+, B-, I use anode D153 as ground.
+24V of CP555, I use chassis ground.
DSP_+5V of CP556, I use pin2 of CP104 as ground.

I have continuity between anode D153 and pin 2 of CP104 but not with chassis ground ?? Is that a problem ? Should all grounds be connected together ?

[Audiorepair]

Yes I believe they should be connected together, or via a low ohm resistor.

Now, what I think may have happened is that you shorted the main Power amps supply to chassis, but the main power amps power supply has the Star ground for its return.
So the current must have run through the chassis and then returned to the star ground somehow.

That somehow could well be the connection between the Star ground and CP501 pins 3 & 4.  The other ends of these gnd pins I think are connected to chassis via the input sockets etc.

So possibly the trace between Star ground and CP501 is the one that fried.

Or a trace on a board connected between CP501 and the chassis.

[Thunderer]

They are not, If I use the right ground reference for each voltage I need to measure, they are spot on, even B+ and B- that were so off before.

I use these as ground reference, anode of D153, chassis ground (any screws on the board) and pin 2 of CP104.

Let's say I want to measure:
B+, B-, I use anode D153 as ground.
+24V of CP555, I use chassis ground.
DSP_+5V of CP556, I use pin2 of CP104 as ground.

I have continuity between anode D153 and pin 2 of CP104 but not with chassis ground ?? Is that a problem ? Should all grounds be connected together ?

Hello, you should not have continuity between the anode of D153 and pin 2 or 5 of CP104. Between them is the C159 (1u/50V). Is there a bridge you created with your spark somewhere between the 2 grounds?



And you are right about references for measurements you took.

[David_AVD]

Are you taking these measurements with all boards installed and screwed in?

Many hi-fi amplifiers use the chassis as part of the ground system, so if you try an run them without everything screwed down there will be issues.

[Audiorepair]

Are you taking these measurements with all boards installed and screwed in?

Many hi-fi amplifiers use the chassis as part of the ground system, so if you try an run them without everything screwed down there will be issues.

Agreed. 
In this case it seems the Star ground and chassis ground are only connected together if the external boards are plugged in.

If they are actually all plugged in as I had assumed, then my previous suggestion would make sense that the shorting issue has indeed burnt this essential ground link open circuit.

[guizmo1967]

Are you taking these measurements with all boards installed and screwed in?

Many hi-fi amplifiers use the chassis as part of the ground system, so if you try an run them without everything screwed down there will be issues.

Yes

They are not, If I use the right ground reference for each voltage I need to measure, they are spot on, even B+ and B- that were so off before.

I use these as ground reference, anode of D153, chassis ground (any screws on the board) and pin 2 of CP104.

Let's say I want to measure:
B+, B-, I use anode D153 as ground.
+24V of CP555, I use chassis ground.
DSP_+5V of CP556, I use pin2 of CP104 as ground.

I have continuity between anode D153 and pin 2 of CP104 but not with chassis ground ?? Is that a problem ? Should all grounds be connected together ?

Hello, you should not have continuity between the anode of D153 and pin 2 or 5 of CP104. Between them is the C159 (1u/50V). Is there a bridge you created with your spark somewhere between the 2 grounds?



And you are right about references for measurements you took.

So If I follow your drawing, I should have continuity between Pin 2 and 5 of CP104 but I don't ! There is also C138 with C159. I wish there was some discoloration somewhere on the board or a burn component but there is nothing so that's why it's difficult for me to find the problem ......

When you say a bridge, you mean through C138 or C159 ?

[Thunderer]

I meant that as long as you have the C138 (good catch!) and C159, there should not be any direct link between the star ground (at the 0V point of the power rails +/-48V).

Between 2 and 5 of CP104 there should be continuity via the "CHASSIS GROUND" as per the schematic.

Though, looking at that schematic, the ground symbol (the rake look-a-like one) is labelled CHASSIS GND, CHASSIS and a third one with no text at all. Page 72 of the service manual.

Good point from our colleagues above: if the connection to chassis is not made, the assumptions I said are not valid (i.e. 2 and 5 of CP104 there should be continuity).

Can you please post some high quality and crisp photos of the back of the PCB? This one, you can take multiple photos to have a better view at the traces.

[guizmo1967]

Hello again !

It's been a month since I've worked on that receiver. From the beginning, even before my mistake (shorted one power transistor collector pin to heatsink), I suspected the main cpu (Sony CXP740096) to be dead ! This receiver, even if there was a fault, should at least turn on the display and flash a led to indicate the fault ?? So this is what I did:

I soldered 5 small wires directly to the cpu pins (VREF, VSS, VDD, RESET and AVDD)

I just plugged the receiver, did not push the ON/STANDBY button and measure these voltages:
VREF   = 5.25V
VSS    = 0V
VDD    = 4.96V
RESET = 4.94V  (active low, so correct)
AVDD  = 4.97V

Checked the murata oscillator (on-chip grounding cap) if it was working, one pin at 0V and the other 4.95V, so not working !!
Removed the murata, soldered a crystal oscillator with two 27pF, like what I do with my microcontroller project and still one pin at 0V and the other at 4.95V !!

So my final though, the main cpu was dead from the beginning .... Not wasting more time on that receiver !!

But what do you think before I throw away (recycle) this receiver !!

[Audiorepair]

So are you saying you mislead us throughout this entire post?

[guizmo1967]

I will not say misleading since I'm no expert !! I just did not know from the beginning of this post why the display would not at least turn on and indicate a fault, that's why I asked for help from more experience members on this forum !!

With everything I tried from your suggestions, I just came to the conclusion that the cpu is dead, I may be wrong .....

Did not wanted to hurt anyone feelings !

[David_AVD]

That sucks, but it's way things go sometimes. Hopefully you learned some trouble shooting ideas from it all.