Harman Kardon AVR1700 won't power up

[rievax_60]

Re: Harman Kardon AVR1700 won't power up

Can't see any shorted transistor causing that.

There are two transistors that have their collectors connected to the top end of the 22k.
Might be one of these transistors' collector tabs making contact with the heat sink

[budm]

Re: Harman Kardon AVR1700 won't power up

Check to see if you can still read DC voltage across that resistor, if it has any DC on it, it will throw off the resistance reading. You will have to make sure to discharge the filter caps for the +/-VCC.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

You may be right, the unit it was turned off, but it may still had some power in it.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

There are two transistors that have their collectors connected to the top end of the 22k.
Might be one of these transistors' collector tabs making contact with the heat sink

There is a pretty big space between the PCB and the heat sink.

[budm]

Re: Harman Kardon AVR1700 won't power up

Do you get good clean sine wave at the Collector of Q513 (differential + input circuit)? The DC reading at the Collector also.

[rievax_60]

Re: Harman Kardon AVR1700 won't power up

There is a pretty big space between the PCB and the heat sink.

The Vbe multiplier transistor is usually attached to the heatsink for thermal feedback to stabilize the output transistors' idle current.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

Do you get good clean sine wave at the Collector of Q513 (differential + input circuit)? The DC reading at the Collector also.

I don't have time right now to check with the scope, but I had a little bit of time to measure the voltages at Q513.
C= 0V
B= 0.098V
E= .704V

[budm]

Re: Harman Kardon AVR1700 won't power up

0V on the Collector is not right at all. Does the front right amplifier which is the same as this one show 0V? The only way to get 0V is that the 18 Ohm voltage dropping resistor is open, there are two 18 Ohms resistor, one for +Vcc, one for -Vcc. Check the Votage on the left side of those two resistors as shown in the diagram.

[redwire]

Re: Harman Kardon AVR1700 won't power up

The readings on Q513 don't make sense - the base should be at 0.0V (unless C503 bad), and the collector positive, and emitter -0.7V; Did you lose the rails with R633 or R638 (18R) open perhaps? They act like fuses.

I just go through and test all semi's in circuit on diode-test. Or compare ohmmeter/diode test readings at same spots between the two channels (with power off). I'll guess you find some shorted and some open transistors, which then pop resistors. I always find it's a bunch of parts that have failed, and if you change most of them but miss one or two, it can roast the new parts.
If you had a bum reading on R603 (22k) you might have a cracked/shorted power transistor.

I find a scope not much help because the amp has feedback so it's trying to correct the signal but can't, making it difficult to figure out where the signal getting blocked.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

Thank you for trying to help, but I'm busy replacing the TV and the repaired H/K AVR with a new set of speaker set I also had to pick up a small cabinet for the new setup from Ikea.
The biggest problem is, that is very hard to measure components, due to the HDMI board beign on top of the amp.
Hopefully, tomorrow I will make some time, to measure the suggested components.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

There are two transistors that have their collectors connected to the top end of the 22k.
Might be one of these transistors' collector tabs making contact with the heat sink

You were right!! When I released the screw from it and pulled the transistor away from the heat sink, the sound came back, loud and clear.
The finals came with that silica(not sure if that is how these are called) from Digikey, I have used one of those here trimmed down to fit.
I haven't noticed, that this transistor that I have used had that metallic surface.
The old one, did not have that.
Thank you guys for helping me with this AVR.
It sounds good!!

[budm]

Re: Harman Kardon AVR1700 won't power up

They are Mica insulator, make sure to use heat sink compound on that mating surfaces. Great work finding the cause of the problem, so the old transistors have the Isolated tab?

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

Thank you for correcting me.
The original transistor's housing, it was all plastic.
Here is a picture with the unit running. Both are less then a year old.

[tom66]

Re: Harman Kardon AVR1700 won't power up

Nice fix, all considered. I just picked up another Yamaha AVR to fix soon, with the single capacitor fault. Will post a thread soon.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

...with your help.
I like my other AVR that I have purchased refurbished, the Onkyo TX-NR609 w/Onkyo 5.1 speaker system. The Onkyo has way more settings then the H/K, but it runs much hotter also.

[tom66]

Re: Harman Kardon AVR1700 won't power up

I wanted to buy a TX-NR609 faulty, but was outbid - went for £88. Common fault is blown final transistor (like this amp), so I do recommend air cooling via fan be implemented. I still need to fix the Onkyo TX-SR506 in the loft, I'm probably going to downgrade it from 7.1 to 6.1 channel and disable the blown channel.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

I know that some Onkyo models suffer from bad HDMI board as well. I think that the 609, 616 have these issues. The cooling is already implemented.
The only problem I'm having with it, that it's a bit noisy.
How can I drop the voltage a bit? TVs USB port.

[tom66]

Re: Harman Kardon AVR1700 won't power up

Amp has a 12V rail that you can use, but it will produce a fair bit of audible noise if you hooked up to 12V directly.

Most fans will run nicely on 7V, so you can use a resistor to drop the voltage. (Most 12V fans work down to around 6V before they will refuse to run at all.)

If your fan draws 0.3A (rating will be printed on fan e.g. 12VDC 0.28A), then you need a resistor which drops 5V (12V - 7V = 5V) at 0.3A, which is calculated using ohms law (Volts/Current = V/I). Solving for this example gets you 16.7 ohms or closest being 15 or 18 ohms, both will work well and you will not hear the fan during operation but it will still provide adequate cooling.

A 15 ohm resistor will dissipate (waste) watts = (5V * 5V) / 15 ohms = 1.6W so use a 3W resistor to be safe.

[tibimakai]

Re: Harman Kardon AVR1700 won't power up

I'm using a laptop cooler which has a 5V fan in there, something like 140-160mm fan. I'm not sure though if anywhere is given the A for the fan. I will check it.

[tom66]

Re: Harman Kardon AVR1700 won't power up

I would use 12V fan like from a scrapped power supply, because most 5V fans won't let you drop the voltage below 4V and they are still nearly full speed at 4V.

I made an error in the power dissipation calculation, realistically it would be closer to 1.5W, I have edited post.