Harman Kardon HK 620 transformer is dead

[meisteris]

Hello,
I have a problem with my amp, which I liked, and I have attempted to disassemble and recap, rewire it, which went rather well, but I have failed to notice, that those thermal isolation's beneath the transistors were missing... So, once I have tried to turn it on, it just refused to do it. When i opened it to see whats wrong, then i saw, that one fuse is blown. And after some poking with multimeter, i have diagnosed that my transformer is gone (short circuit all ower it). Once i have removed it, i poked with multimeter some more, and decided, that all the components on the main board are (or at least should be) OK.

Maybe I could find something similar for replacement. But I do not know any technical specifications of it. I do not even know how much voltage and current it should produce. I have spent hours searching for service manual, or schematics for this amp, but all the links seems dead, so I am desperate and asking for help here.

If someone has a service manual for this amp, please could you share? If not, then any advices about finding the technical data I need, are very welcome.

If that helps, i see couple numbers on the transformer itself:
5584-T4402
IK 4L2 TK

But at least I was't lucky to find anything useful with these numbers.

Thank you very much in advance, if you need any more information, I will do my best to provide it.

[GoranB]

Are you sure your trafo is dead? If you are meassuring the secundar it will show short circuit and thats the way should be. In fact there is some resistance but very low. Long time ago i was repairing the HK610 and i remember that trafo was 25-0-25 about 200W, for HK620 the voltage on secundar should be little higher but i cant tell precisly.
I still believe your trafo is good.

[labjr]

Doesn't seem very likely that the transformer is bad. I'm wondering why you would need to recap or rewire in the first place? Seems like you don't have enough experience to do this anyway because you are causing more damage by your mistakes.

Which fuse is blown?

[meisteris]

Hmm, now you got me wondering, well in the output side, between V-Gnd-V connections, i have chort circuit multimeter shows .000 . Next to those trhee connections, i have two separate for somethigin, again .000 between them. On the input side, where 220V is connected, i've also have .000 between the wires. If that does not mean anything bad, then i would be interesdted in how this transformer should be tested I also tried to smell it, and it has no bad smell, visually it seems fine.

[GoranB]

Your output transistors are damaged, and maybe more ... drivers also, nothing wrong with your trafo. It would be the best to ask for professional help, some electronic service in your place.

[meisteris]

it is written 250V 1.6A on the blown fuse. I needed to replace some leaked capacitors, thats why. And i did not liked the original thin wires, so as it did not seemed too hard, and the unit was taken apart allready, i just took the oportunity to replace them with slightly thicker and better quality ones. Thas all. I have some skill with soldering, but in electronic stuff i am more like a beginner.

[simon7000]

Originally Posted by meisteris

Hmm, now you got me wondering, well in the output side, between V-Gnd-V connections, i have chort circuit multimeter shows .000 . Next to those trhee connections, i have two separate for somethigin, again .000 between them. On the input side, where 220V is connected, i've also have .000 between the wires. If that does not mean anything bad, then i would be interesdted in how this transformer should be tested I also tried to smell it, and it has no bad smell, visually it seems fine.

Just using test leads should give you a higher reading than .000 ohms! Put it back in and connect the primary but insulate the secondary. Turn it on through a light bulb box.

[meisteris]

Originally Posted by GoranB

Your output transistors are damaged, and maybe more ... drivers also, nothing wrong with your trafo. It would be the best to ask for professional help, some electronic service in your place.

I agree, that seeking for professional help is probably fastest way to get that amp working again. But, I would like to take this opportunity to learn something from this. Electronics, is interesting world for me Plus if damage is that serious (repairs would cost a lot), then I'll just find another amp for me. But until then, lets learn

Ok, if transformer not dead, that means I should check transistors. There two little ones at the sides of board. There are total four of bigger ones and on weird looking in the middle. I am assuming that those should be taken out in order to test them, right? If they turns out OK, what next I should check?

I kindly thank for your (and everyone else s) time on these questions of mine

[meisteris]

Originally Posted by simon7000

Just using test leads should give you a higher reading than .000 ohms! Put it back in and connect the primary but insulate the secondary. Turn it on through a light bulb box.

Now I am confused one person says it's OK, and you say it may not be OK.

Well, i too think that i should see some more Ohms. Plus there is also a werid thing, that if i connect it back to board, then i get short circuits everywhere. Even if i take ground from a metal case of the amp, and with other tester lead check all the places where i know is a +, i get same .000 output. And then when i remove the transformer out, then on the board all goes back to normal.

[labjr]

What you should do first is disconnect the power supply from the amplfier, replace the fuse and plug it in to check for voltage.