Harman Kardon AVR 3700 blown standby power supply

[jacampb2]

Re: Harman Kardon AVR 3700 blown standby power supply

Ok, here goes. Please excuse my horribly messy test bench. It is on the very fine edge of organized chaos!

I'm going to do my best to explain what I have done, but keep in mind that I'm not 100% sure I am doing things exactly right. This is a bit of a case of the blind leading the blind...

**Edit** the capacitor in series is a 10nf polypropylene that I had around.

This one is the bad Harmon Kardon transformer, trying to show the whole test setup. Signal generator is 1Khz square wave for all tests.



Close up of the bad transformer on the breadboard.



This is a picture of the "ring" on the bad transformer, notice how there are almost no oscillations, I believe this is because the short changes the "Q" of the transformer, but I think that the root of it is that a short will electrically be more similar to a piece of wire than coil. This may be completely of base, please someone correct me if that isn't the case.



This picture is just a small SMPS transformer I had around to show a good transformer under test. Same setup, had to use jumper wires for this one, it is to big to fit the breadboard. The is not the same type of transformer, but I don't think it invalidates the example.



Close up picture.



Good transformer "ringing" under test



This is just an example of the same good transformer, but I have jumpered the other primary winding, just to show an example of what I read about online. It doesn't actually matter what winding is shorted in the transformer, any shorted winding will drastically reduce the "Q" of the whole thing. I am not going to pretend to understand why. I think that level of math is above my pay grade



Shorted primary winding "ring" waveform.



Same setup as above, but this time with one of the secondary windings shorted.



And, pretty much the same results.



That's good enough for the girls I go out with. I hope it helps. Also, if you smart and formally trained folks have a better explanation of what is going on, I would love to hear an explanation that is a little bit "dumbed" down for those of us with no formal education if it is at all possible.

Thanks again for all of your help.

Sincerely,
Jason

[tibimakai]

Re: Harman Kardon AVR 3700 blown standby power supply

Nice.
Which generator is that?

[budm]

Re: Harman Kardon AVR 3700 blown standby power supply

How high is the 1KHz output signal did you set the generator to?

[jacampb2]

Re: Harman Kardon AVR 3700 blown standby power supply

Nice.
Which generator is that?

I initially found it on eBay listed as JDS6600(IIRC), but I ended up buying it on Amazon to get it a bit faster. It starts around $85 on ebay, a bit more on Amazon. The one from Amazon came with two sets of output leads, so you don't need to buy more unless you want something special. Here is the amazon link, Amazon arbitrary function generator.

How high is the 1KHz output signal did you set the generator to?

It's set at 5V p-p. I wasn't sure how high to go with it and I didn't know if the back EMF generated had the potential to hurt the function generator. It seems a lot of the "ring tester" meters out there for build or sale derive their square wave from a 9V battery, so 5V p-p seems a safe place to start. One thing I did read is that if the insulation is only compromised so that it arcs over under high voltage conditions, it's possible for a transformer to appear to have good Q, but still fail under operating conditions. From my understanding, that is more a issue with the HV flybacks in CRT TV/monitors.

Thanks,
Jason

[Jasonoff]

Re: Harman Kardon AVR 3700 blown standby power supply

Digging up a thread from the dead with my first post.

Had my PS board (PN: COP12475E) take a dump today. Looks like it has been slowly dying while all the caps oozed out. Zone 2 amp can power on no problem, but the main amp will shut off after 5 seconds or so.

I'm in Canada but could order from the US if necessary. Does anyone know where to buy HK parts?

I have an email out to the CDN rep which just appears to be a distributor (Erikson Consumer).

[Jasonoff]

Re: Harman Kardon AVR 3700 blown standby power supply

After closer inspection it's just glue around all of the caps.

[tibimakai]

Re: Harman Kardon AVR 3700 blown standby power supply

Most likely, one or more of those 8 pin ICs are shorted.
On my previous 1700 model repair and somebody else, who had the same model as you, the standby transformer it was bad, TF91, if I remember correctly. I had to order those ICs from Aliexpress. Maybe, some of the zener diodes could be bad as well. 16V and the 18V ones.

[Agent24]

Re: Harman Kardon AVR 3700 blown standby power supply

Is it just me or is C944(?) (Small electrolytic bottom right of photo, in-between two larger ones) looking a little bulgy?

[prabhuviji]

Re: Harman Kardon AVR 3700 blown standby power supply

Hi
I'm also having similar problems with avr3700 PS. It is totally dead with IC91 burnt.
I'm trying to order parts from HK International in US and their email ID is hcgcustomersupport@harman.com
I'm still in the middle of troubleshooting and found the Zener diode D928 is short. I'm thinking of ordering the TF91 transformer as previous post's I have read seems to have this transformer problem.
I'm in Canada and trying to order parts from US.

[Jasonoff]

Re: Harman Kardon AVR 3700 blown standby power supply

Most likely, one or more of those 8 pin ICs are shorted.
On my previous 1700 model repair and somebody else, who had the same model as you, the standby transformer it was bad, TF91, if I remember correctly. I had to order those ICs from Aliexpress. Maybe, some of the zener diodes could be bad as well. 16V and the 18V ones.

Thanks for the suggestions. Are you talking about IC91 & IC92?

I would assume if the standby TF91 was bad, standby power wouldn't work? If I unplug CN20 it stays powered with both zones on so I have a feeling it's something on the amplifier board for the main zone. I had the power board out to inspect it closely and it looked fine visually. When I put it all back together (forgot to plug in CN20) it appeared to be working. (magically fixed!) I wired it all back up to test and had no speaker output. Plugged CN20 back in to resolve that issue and it worked for about 10min. Maybe something thermal, expansion, component overheating?

I ended up snagging a deal on a new receiver so I haven't done any real troubleshooting yet.

Is it just me or is C944(?) (Small electrolytic bottom right of photo, in-between two larger ones) looking a little bulgy?

Optical I think. She looks fine.

Hi
I'm also having similar problems with avr3700 PS. It is totally dead with IC91 burnt.
I'm trying to order parts from HK International in US and their email ID is hcgcustomersupport@harman.com
I'm still in the middle of troubleshooting and found the Zener diode D928 is short. I'm thinking of ordering the TF91 transformer as previous post's I have read seems to have this transformer problem.
I'm in Canada and trying to order parts from US.

Post back what you find out. I have called, left messages and emailed. No response from the CDN rep. Apparently HK has been bouncing around ownership. Latest rumor is Samsung buying them. I don't think they care about their receiver line anymore.

[prabhuviji]

Re: Harman Kardon AVR 3700 blown standby power supply

Thanks for the suggestions. Are you talking about IC91 & IC92?

I would assume if the standby TF91 was bad, standby power wouldn't work? If I unplug CN20 it stays powered with both zones on so I have a feeling it's something on the amplifier board for the main zone. I had the power board out to inspect it closely and it looked fine visually. When I put it all back together (forgot to plug in CN20) it appeared to be working. (magically fixed!) I wired it all back up to test and had no speaker output. Plugged CN20 back in to resolve that issue and it worked for about 10min. Maybe something thermal, expansion, component overheating?

I ended up snagging a deal on a new receiver so I haven't done any real troubleshooting yet.

Optical I think. She looks fine.




Post back what you find out. I have called, left messages and emailed. No response from the CDN rep. Apparently HK has been bouncing around ownership. Latest rumor is Samsung buying them. I don't think they care about their receiver line anymore.

Hi Jason
I need some suggestion in troubleshooting my receiver. I don't have any signal generator or Scope to check the transformer, but I have ordered a new TF91 from US harman Kardon. Shall I go ahead and replace the IC91 and zener to try it out before receiving the transformer TF91 by shipment. (I do have several IC91 chips so no worries if it burns again). Any suggestions will be greatly appreciated.
Prabhu

[kc8adu]

Re: Harman Kardon AVR 3700 blown standby power supply

looks like d921 has been running very hot.

[ogibon]

Re: Harman Kardon AVR 3700 blown standby power supply

Hello,
Does anyone have a full service manual?

Bartek

[R_J]

Re: Harman Kardon AVR 3700 blown standby power supply

This should be the service manual

[dvd4me]

Re: Harman Kardon AVR 3700 blown standby power supply

Hello,

Long story short..

I have the same issue with this AVR3700, the main fuse blown and the D901 D902 shorted,R928...R971, the 10 ohm resistors also burned. I ordered the diodes and resistors from Newark,
I also noticed the most common issue, the 2 C983 and C984 of 471/1kV caps that were browned... I put them on the order also.
These should come in next week.
The chip OB2358AP was cracked, I did ordered from china but it will take some time to get here.
On eevblog I saw some references of an ikea led lamp that contained the similar PWM type chip. I bought one used lamp with the same type of adapter to harvest the chip and use-it later as a test bench for the ordered chips that will come later on.
The last culprit is the transformer that I could not find as a part easily.
I tested with my Mega 328 LCR-T4 meter and the primary winding was only 1 ohm, clearly shorted.
I have the pics of the cooked wire of the TF91 primary winding that had no chance to survive when it had to blow the 8 Amp main fuse..

I started to dismantle the TF91 transformer, the first one like this in my life.
It was not easy, I heat it up with a medium heat gun from amazon, quite hard to separate the 2 ferrite core pieces. I managed to break the plastic base of the coil, very thin plastic btw. I also dropp -it by mistake on the floor while trying to remove the other ferrite half, one arm of the ferrite broke also..

After many hours of trials I managed to rewind the transformer and also put-it back, align the ferrite properly (it has a middle air gap), glued to stay nice.

I will post more updates soon.
Regards

[dvd4me]

TF91 in Harman Kardon AVR 3700 blown standby power supply

The pictures below are with the schematic of AVR3700 power board showing the blown parts and the transformer winding count. The windings are not exactly the same as in the AVR 370 schematics for the secondary part, the 5V standby is winded with a double 2 wire layer, both layers connect to pins 5 and 6, I edited the picture to show that. Also winding 9-10 in the schematic is actually.. 7-10 on the transformer! It ads up to the voltage of the 5V stand by.

So it must be some revisions on that transformer to reflect the changes, maybe it depends of the 110V/220V versions.
Regards

[dvd4me]

Re: Harman Kardon AVR 3700 blown standby power supply

You rewind them. Done that a couple times. It's not that difficult once you get the hang of it. But that's coming from someone who has built SMPS'es from scratch including hand-wound transformer with re-used bobbins and cores.

Fratele meu, Bro, I spent hours to redo the windings on this little piece of s*it!
I found another one to reuse the core I broke an arm when removing and they are not the same core, one has air gap the other one no...
Nici mesterul Manole nu se chinuia asa la zidit..
What a pain... Cheers