Harman Kardon AVR1700 not powering up

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I have took some more measurements.
With ground connected and probe near the transformer(trf_close).
Second is at the anode of D911(d911_diode).

[Agent24]

Re: Harman Kardon AVR1700 not powering up

I've re-attached your pictures here as JPG so they're easier to view. If you attach more, please convert them to JPG if you can so the forum can show them.

Well, the chip is indeed running at 50kHz as it should be (from the first picture), so at least it's doing something right.

Can you zoom in on the transformer waveform from the first picture and show it at the same 500nS timebase as the diode one?

You are using x10 probe?

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

This way, I could actually see something, on the screen. That is, why I did not go lower on the scale.
If I convert the pictures in jpg, they will show on the forum? Thanks for that. I will do that, in the future.

[Agent24]

Re: Harman Kardon AVR1700 not powering up

You may need to adjust the trigger level or voltage per division? In any case, once the wave is captured, you can zoom in?

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

The truth to be told, I don't know what I'm doing with the scope, but I will give it another try.

How do you zoom, with the scope?

[Agent24]

Re: Harman Kardon AVR1700 not powering up

What is the model of your scope?

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

Rigol DS1052E, converted to 100Mhz with firmware.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

Found these:
http://www.righto.com/2013/07/tips-f...l-ds1052e.html

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I hope, that I did it right.

[Agent24]

Re: Harman Kardon AVR1700 not powering up

That waveform doesn't look particularly good. There should be more oscillation there. Can you try again but see if you can capture just one of the pulses? I'm wondering if the scope is averaging out the waveform and making it look wrong (can happen). Try reducing the timebase setting and re-capture.


Can you also provide screenshots of the waveforms for each of the output pins of the transformer?

Make sure you measure them with reference to the secondary side ground, not the primary side ground you as you have been using for the others.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I don't think the second time is any better, but I have tried. I actually, touched the core.
At the secondary, I took measurements at the diodes, D921(second picture) and 943(third picture).

[Agent24]

Re: Harman Kardon AVR1700 not powering up

You did nothing wrong, it's just that the transformer oscillations are being dampened by something. Your new screenshot of that pulse proves it.

From the screenshots, it looks to me as though there is a problem in the output feeding D921. You can see how the oscillations die away much faster than at D943 or D911 in your previous screenshot.

Either there is a shorted turn in the transformer on that output (unlikely) or D921 or something after it has gone shorted\leaky.
Have you tried replacing D921 at all yet? I know you said you tested it and it seemed OK, but it could be failing under load.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I have removed D921 and measured it again (first picture).
I have got the optos in and replaced PC92 opto. I have got the wrong package though. I have got by mistake, surface mount and I had to turn the legs outward and soldered it, at the bottom of the pcb.
I did not have time to do much today, but I have measured quickly the primary side of the opto (second picture). I don't have a before picture, to compare it too.

[Agent24]

Re: Harman Kardon AVR1700 not powering up

Running without D921 will likely produce false results as it supplies the feedback circuitry, so the overall circuit probably still won't work. The waveform does look better, though. What does the general transformer core waveform look like now?

The feedback pin of IC91 has an internal pullup resistor to an internal 5v supply, so it makes sense you see 5v there. The opto would start to pull this low when the shunt regulator IC96 turns on.

Try replacing D921 with a brand new diode and see what happens.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I have measured the diode, out of the circuitry and it showed .231V. That is normal? Is not to low?
It seems like, a NTE578 is an equivalent. I think that, I should be able to pick it up locally, if it is good.

[Agent24]

Re: Harman Kardon AVR1700 not powering up

0.2v is normal for a Schottky diode. It might be fine, of course, but without replacing it or testing it on a curve tracer you can't say for sure. An NTE578 would be fine as replacement.

If the diode is not the problem, the only other likely components to cause a problem are the decoupling capacitors on that ST5V rail. C979 (near D921) and C963, C964, near the output connector BN65. They are ceramics, which sometimes fail shorted or could also have some kind of leakage\breakdown problem.

Another (but less likely) possibility are the electrolytics, C944 and C929.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

The three capacitors, look good. Measured them out of circuitry.
I still have to get the diode, though. In the weekend.

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

I had an accident with the ps. I tied using the wick and I have managed to drag it across the primary and shorted out D904 and R911. R911 was open. I have replaced it, but it is still not enough.
At D911 I still don't have the voltage back.
I will need to test some more components, to see which else get damaged.

[Agent24]

Re: Harman Kardon AVR1700 not powering up

Probably you blew the main fuse?

[tibimakai]

Re: Harman Kardon AVR1700 not powering up

The 335V is OK.
I don't have the voltage, at D911.