Harman Kardon AVR1700 won't power up

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

A leaky capacitor can cause a short?

[tom66]

Re: Harman Kardon AVR1700 won't power up

Uhh, sort of. In repair/diag. terminology leaky typically means not shorted (sub 1 ohm) but low enough resistance to cause problems.

IC92 could still be defective. If the internal silicon is damaged, you can get lots of strange readings across all pins because the die has overheated.

The soft start pin basically acts to limit the initial charging current that is drawn from the mains when the unit is plugged in. The capacitors on the output are empty so charging them up takes a lot of power which can cause undesired effects including excessive EMI, damage to fuses, etc.

Basically it acts as a little timer which controls the maximum power the IC can deliver. As the capacitor charges up, it lets more power go to the output (sort of like a throttle.) But, if the capacitor is leaky, the charging circuit will not allow the voltage to rise, and the soft start will stay at almost 0%.

A quick look at the datasheet shows that the soft start charging resistor Rsoft-start inside the IC is 50 kilohms nominal (42~62kohm range) powered from a 6.5V supply. To turn the IC on it needs to reach at least 5.3V. If the capacitor acts as a 200 ohm load, the maximum voltage it can reach is about 0.02V, well below the start up threshold. (Read up on RC charging circuits if you want to learn more.)

Time to reach ~63% of input supply: R*C
Time to reach ~95% of input supply: 3*R*C
Time to reach ~99% of input supply: 5*R*C
(keep units: 1uF = 0.000001 farads, 1 kohm = 1000 ohms)

Read the above and understand it, tell me what YOU think the SS pin voltage should be.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

I have removed the capacitor and outside of the circuit did not have that low value, it was in mega ohms. I have measured the two pads and there it was 190 Ohm.
When it was in, at the S/S pin I have measured 4.4V and from that voltage, it was keep dropping to something like 0.35V.
Sorry about not answering to your quiz question, but I barely have time to do these measurements. When you have a five years old, it robs all your free time.
What is interesting, that the values are not always the same. After re-soldering the C903, I have measured 125 Ohm over it.
The voltage that I have measured yesterday(13.75V), now is again 15.xV.
I will just order this IC.

[tom66]

Re: Harman Kardon AVR1700 won't power up

Readings are too inconsistent to make any conclusions but you may have contamination on the circuit board. Is the IC SMD or DIP?

Repairing electronics takes a LOT of free time, sorry. And it will not always be the case that someone will be here to help you. So you should try and make more of an effort to learn diagnosis techniques; in this case, everything I mentioned is available by reading through the datasheet for the particular control IC, which can be found for free on the internet. I spent 10 minutes skimming through it to find the information.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

The IC is DIP.

I know that it takes a lot of free time to repair electronic devices, which unfortunately I don't have for a while. I won't be learning much for a while. If nobody will bee here to help me, I will put that device away for a while, or I will sell it to somebody else.
I have read through it's document, but I haven't understand much. I have never studied any kind of electronics, I'm only a machinist.

[tom66]

Re: Harman Kardon AVR1700 won't power up

Well, the answer is: SS must be 5.3V to turn on the IC.

I am currently directing most of my posting time to people on the forum who are individuals and have their own TVs/electronics to fix, to save them from landfill and to reduce over-consumerism, and then I direct it to people who repair them as a hobby, then a business. So do excuse me if I don't get to you, which in part is why I'm trying to help you with solving the problem rather than just telling you outright, but if you don't care for this then I'm not sure if there's much point in me trying?

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

I do care and I appreciate it a lot. I even wonder, how do you have all this time to help others and so fast? You, Bud and a couple of others are doing an amazing job on this forum.
I guess, you guys don't have little kids to bother you.
I shouldn't even work on repairing devices until my daughter grows up a bit more, but all started unexpectedly. My wife found a TV at our dumpster...

So back to this device. Just a heads up, this week I should be getting another one of these receivers with a blinking power LED. We can compare the to units.
SS is Soft Start if I understand correctly. There is a 5.6V Zener diode at that pin, so it should be 5.6V, no?

[tom66]

Re: Harman Kardon AVR1700 won't power up

5.6V zener would limit it to 5.6V max, +/-10%. The zener could be leaky, too, consider that.

I'm free until the 5th of June when I go back to work in a 9-5 job where I get paid to do something I love (Electronics Design Engineering.) I'm currently on a break waiting for my last exam.

As for budm, I'm not sure, but I think he does some repairs as charitable work, which is a great thing to do.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

So, lets say we start this IC, what should we expect then? We can expect more bad components or the unit should work?
This IC starts up the other power sources?
I didn't understand why we couldn't separate each power source separately?
They work together, and if one fails the chain is broken?
Do you think I should replace the capacitor too? If I understand correctly, it's a 0.47uf/50V capacitor?

[tom66]

Re: Harman Kardon AVR1700 won't power up

The IC provides the +/-12V, plus the Vcc (13.5V) for turning on the +/-45V supply.

Why are they chained? I'm not sure, the best person to ask would be the designer. However, I can make a quick guess. It's an easy and cheap way of ensuring the supplies stay synchronised. They probably want it so that when power suddenly goes, the +/-45V drops out, then the +/-12V and finally the 5V standby. This gives the amplifier time to shut everything down without making a large "pop" sound. See, if the amplifier output +/-45V is still present but the +/-12V analog is gone, the output can go wacky and make unpleasant noises. Ever see old CRTs switch off? Notice that flash on the screen when they turn off, because they use a single power supply circuit for everything? Imagine a similar pop from the loudspeakers. Not pleasant.

If the capacitor is ceramic, leave it for now.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

Tom, do you think that I should replace these Acon capacitors with some Panasonic ones? I'm intending to keep this receiver for myself.
These capacitors are all over this receiver, should I replace all of them?

[tom66]

Re: Harman Kardon AVR1700 won't power up

If you intend to replace them, I would focus only on the power supply for now. Other places are unlikely to cause problems. Since it uses a switching power supply, the cheap caps near the output will be under a lot more stress and could fail early.

First though, you need to track down the fault, I guess that means waiting for the IC to arrive.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

I'm still waiting on the IC. The other receiver will arrive today. I'm just thinking that I don't want crapy capacitors in my own devices.

[tom66]

Re: Harman Kardon AVR1700 won't power up

Yeah, but in the audio processing stages you're going to find hundreds. You'd have a lot of work. I don't like crap caps in my equipment, but I only ever re-cap the power supply, unless the other parts have a history of failures.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

Second receiver came in. That one turns on for two seconds and turns off with power light blinking.
I have unplugged the +/- 45V connector and powered right up. I guess some of the power transistors may be shorted. It uses D2390 with D1560.
How would I check these with the DVM? It shoud show as regular PNP and NPN transitors?

I have removed the power supply from this one and transferred it to theold one.
Fired right up. It seems like all functions work, but I couldn't get a sound out of it yet.
I have just placed an order for a remote.
I'm keep playing with it, maybe I can make it get some sound out of it. I have got some sound out of the subwoofer output.

[tom66]

Re: Harman Kardon AVR1700 won't power up

If you get no sound from the unit the format is probably set wrong. Try setting the mode to Stereo or use one of the stereo RCA audio inputs. I know every time I touch my dad's Yamaha, the one I fixed, which isn't even an advanced unit, I manage to screw up the audio settings on it.

Yep, the other one probably has bad transistors, in most cases this is in fact visible if you look at them, you will see one is blown out. But you can find the bad channel. Find the power signals before they go to the speaker protection relays, near the outputs. Test each. Any channel showing more than +/-0.5V after start up is probably bad. As for testing transistors, just test for shorts between all pins on diode mode.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

Already found a B1560 shorted between two pins. The rest looks good.
Placing an order at Digikey.
Do you think that is safe to remove that transistor and power it up, to see if it goes back to protect mode?
There is a connector on the board that says Protect test (short). What do you think is for?

[Khron]

Re: Harman Kardon AVR1700 won't power up

In class-(A)B amps, if one of the "sides" is blown (in this case, the 2SB1560), it's better to replace its counterpart as well (the associated 2SD2390).

[tom66]

Re: Harman Kardon AVR1700 won't power up

Replace the complementary transistor, the driver transistors, the sub drive transistors, nearby capacitors, base resistors, and the emitter resistors, or you may well regret it and do more damage to the amp.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

I will replace that transistor too. I have noticed on Ebay that they sell them in pairs. I will buy two sets from Digikey, just in case.
I will check on those other components as well.
I have kept playing with it yesterday and a bit today and I have realized that if I use the headphone I can hear music from a USB stick and radio, but though the speakers, nothing.
I have opened it up again and I have found missing +/- 45V on the PS board.
I guess, if everything else works, this is the only voltage missing.
So this power supply has it's own issues as well. I was to excited that I have seen something on the display and I thought that is all well.
I will have to take it apart and do some more measuring.