Ok so i got a hk 730 twin power. In peices and in boxes. All back in one piece. Not sure where the output transisters go in order on the heatsink. 2 red letters 2 black different part numbers. ....cant find any info. Also all caps done and a bunch of undered valued resistors changed ....and one side of the output board. Smokin hot. Where the ceramic resistors smoke. If the transistors are suspect. Whats a good substation part number is ok.
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Hk 730
- Thread starter Tdk67
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xrayspex77
Super Member
This is the Amp Section Schematic from the Service Manual which is on HiFi Engine https://www.hifiengine.com/manual_library/harman-kardon/730.shtml
You have to register to download but it's free and you won't get spammed by them. Trying to get mine working properly again, worth the effort.
You have to register to download but it's free and you won't get spammed by them. Trying to get mine working properly again, worth the effort.
Yes i ha
have and there good ive actualy changed them. And when i did it smoked a resistor. Funny. When i changed them out the rear one got hot and the ceramic resistors ckracle they got so hot. Now its back to the front. When i plug the driver board in it blows the main fuse in back. And i can here a spark on the amp board on the front connector. Like discharging a cap. But ill be dammed if i can find a short. Anywhere. With the amp board unpluged alls good. Pluged in pop.I found this pic on the net. Have you tested the output transistors?
Raccoon1400
Super Member
Have you tested them with diode check after you realized they were in the wrong spot? Also, are the mica insulators that go between the transistors and the heatsink in place?
Blue Shadow
Waiting for Vintage Gear from this century
Time for some review of how to read a schematic to determine where the transistors go as well as the learning the tutorial about these BJT and building a dim bulb tester before this unit gets plugged in again.
Yes has insulators. And they were in the correct spots. Hi fi engine schematics very poor couldnt read numbers for location. ...diode check all 4 ok.
One of them did not have insulator only compound. As i said got it in pieces in a box. Found the last insulator. Same thing. Getting super hot on that one channel. Specs are the same on all componets on both sides. Only heating up on one side. ....im gonna microscope these solder flows yet again to see if solder has bleed anywhere it shouldnt.
Raccoon1400
Super Member
Check for shorts in the rectifiers and the transistors in the power amp stage before the outputs.
Also, build and use a dim bulb tester if you haven't already. Pull the driver board out completely and see if the dim bulb tester stays bright, and check the rail voltages.
And keep in mind that any time you power it up without the dim bulb tester and you have these issues it is possible something blew, so check the outputs again in the channel that was missing the insulator.
Thanks. Everything is ok on the power supply side. ....the power output transistors are ok. The transitors on the driver side must have a issue. Im gonna remove some and take a look. Its a simple board. All the resistors all in spec...i hope these tranistors are easy to locate i have tons but i doubt that number. And these online cross reference sites arent very good.
Raccoon1400
Super Member
If you need any new replacement part numbers I know replacements for the whole board.
Make sure you don't power it up again without a dim bulb tester. I also like to be watching the bias current on a meter as I'm powering up something like this. If the bias current is way too high I shut it off immediately and that tells me there is a problem in the channel that the bias spiked on.
You can also check for a short without removing transistors. Just use your ohm meter.
Its a pretty simple board. ...but the series of transistors looks as though thats where my issue is. They do vary. And one shows shorted ...a board would be nice looks like soneone has installed a few 1/4 watt resistors at one point ...where 1/2 watt are called for. The values are correct. And noted from the factory on the pcb. These transistor numbers are not. Matching any of my cross refrences. A new driver board is my beat bet. Your right. As i said i boought this in pieces. And there werent even any caps on any board. This is my last piece. Strange how when i first got it together and turned it on it worked ..then only the right channel got hot and smoked. Now left. ....like a mobile short. Ive done tons of these. Im missing somthing. Your help is really apreaciated...
Raccoon1400
Super Member
I wouldn't count on finding a new driver board.
Can you post a picture of the board? Everything on the board is replaceable. I have one of these here if you need some pictures of the board with correct parts installed.
Yes i will as soon as i get home. Give me a few hours. Ok
Is there any cross referece on the transistorsn. I have boxes of them. And that would surly help. And have some old boards around.
Raccoon1400
Super Member
You don't need a cross reference sheet, just look at the datasheets.
Checksum47
New Member
Raccoon1400, do you think you can post any replacement part numbers for anything that you would upgrade if doing a complete re-cap of the HK 730? I just figured since you mentioned that you had something like that... It would be a HUGE help to me. Thanks either way...
Checksum47
New Member
Raccoon1400 I dont know if you're still around but do you happen to have those replacement part numbers for anything worth replacing on the HK board???