Harman Kardon AVR1700 not powering up

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

D910, D928, are OK, D921 shows a bit weird 0.24V, slowly rising and is OK the other way(I have removed it as well), and D943 OK in one way and 0.49V the other way.
TF91 pin #1 & #2 is 324V(today, is 324V and not 334V as yesterday).
PC92 has 0.13V on the primary side.

[budm]

Re: Harman Kardon AVR1700 not powering up

If you are getting around 18vdc at VDD pin of the IC then it should start running and see 5VDC on the filter cap C944.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

With min/max(only) I'm seeing 0.5V.

[Agent24]

Re: Harman Kardon AVR1700 not powering up

What exactly do you get when you measure D921 and D943? When you say OK one way and a voltage the other way, what you do mean?

Which way do you get which reading? Forward biased or reverse biased? I'm confused as to what exactly is going on with the diodes.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

A diode should show around 0.6V, right? These two show less, one is 0.24 and the other is 0.49V.

[budm]

Re: Harman Kardon AVR1700 not powering up

Pin 3 Voltage is really low @ 0.13V, if you at the internal diagram of the IC, there is pull-up resistor that is connected to the internal 5.7V supply, when the circuit is working the opto PC92 Photo transistor on the receiving side will conduct more when the output of the secondary side trying to go up so the Voltage at FB pin will be lower.
The VF of the LED in the OPTO is around 1.5~2V range, you have to look at the spec sheet of the OPTO. If the OPTO should not be on if there is no DC in the colde side to turn on the LED inside the opto so FB pin 3 should be higher than 0.13V.
So IC91 is new IC? Resistance on pin 4 is also around 2 Ohms or so?

[budm]

Re: Harman Kardon AVR1700 not powering up

A diode should show around 0.6V, right? These two show less, one is 0.24 and the other is 0.49V.

schottky diode will have low Vf compared to regular silicon diode, Vf value is also depends on the current flowing through the diode, more current = higher Vf up to the spec point.
If in doubt you can always use variable power supply and current limiter to check the leakage current and the Vf at difference forward current value.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I will look at the opto, tomorrow. Thanks for helping. Have a good night.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

Did not give up, I just did not have time for this.
Wife broke her arm, so I'm busy with house stuff.
On the side, I have repaired two Onkyos, with blown amps.
Soon I will be back.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I'm an idiot, I have cut the trace at the 18V zener diode to check for the 18V and I have forgot to join that cut.
The oscillating Vcc is back and at the opto is an oscillation as well. Maximum that what I have read is 1.5V, but I did not check it with min/max yet.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I measure 3.8V at that opto, with min/max. It is oscillating.
IC91 is a new IC.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I'm not getting 5V at C944.
I have even swapped two optos between them, and there is no change.
All I'm getting there, is some super slow rising milivolts.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I was trying to see with the scope what oscillation do I get there and by touching only with the scopes ground, I'm blowing the 8A fuse. Why?

[Agent24]

Re: Harman Kardon AVR1700 not powering up

I was trying to see with the scope what oscillation do I get there and by touching only with the scopes ground, I'm blowing the 8A fuse. Why?

Are you using an isolation transformer? You need to and this may be why the fuse blows, if you do not have one. It may also be because of a fault somewhere. Hopefully someone else can advise.

https://www.youtube.com/watch?v=xaELqAo4kkQ

[Agent24]

Re: Harman Kardon AVR1700 not powering up

I measure 3.8V at that opto, with min/max. It is oscillating.
IC91 is a new IC.

On which pin exactly?

I'm not getting 5V at C944.
I have even swapped two optos between them, and there is no change.
All I'm getting there, is some super slow rising milivolts.

Have you checked D921 out of circuit?

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I wasn't aware of those thing, thanks for that video. Did not use an isolation transformer.
D921 is good, I have checked it, out of the circuit.
At the IC91, I'm talking about the pin #3, that goes to the opto..

[Agent24]

Re: Harman Kardon AVR1700 not powering up

What if you disconnect the jumper J906 or J914 which provides power to the IC92 circuit (from between R932 and D911)? Maybe there is some excess current draw from that circuit which is pulling down IC91's VCC and causing it to go into a restart loop.

Also, did you check R932? How about the 10 ohm resistors from IC91 pin 4? Five of them in parallel should be 2 ohms. If it's different than that, maybe one or more is bad.


If that doesn't help, I wonder if the TL432 (IC96) is bad?

Have you checked for any shorts to ground from the cathodes of D921 and D943?
Checked IC99 for shorts on output?

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I will come back to this, in the next couple of days. I'm "fighting" with an old repair, that I have put away. It is a Pioneer VSX1122K which is dead.
Trying a thermal camera, to find a short. I have borrowed this small android camera and I will need to give it back.
It is really cool to use this type of camera, for finding shorts. Whithout it, I would have not looked in that area.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I have removed jumper J914 and there was, no change.
R932 is good, at 4.7 Ohm, D911 is good as well.
The bank of 10 Ohm resistors are all good, there is 2 Ohm between them.
There is no short, at IC96 either.
There is 253 Ohm, between D921 cathode and ground, at D943 is more then 200 Kohm.
There is no short, at IC99 either.

[Agent24]

Re: Harman Kardon AVR1700 not powering up

Where did you swap the optoisolator from? Have you tried with a brand new or known good one?

http://www.edaboard.com/thread82821.html shows a test circuit. You can switch the 10k resistor in and out of connection to the opto. The LED should turn on and off.