Harman kardon avr-247

[Jtroutt19]

Hey guys so here is what i got going on. I was given this unit and it was not producing any audio. Upon inspection i found some swollen caps amd burnt resisters on a couple of the audio out channels. I recapped the entire audio board with panasonic high quality audio caps gold series. After i did that unit would come on and for 3-5 minutes and shutoff in protect mode. Turns out a few transistors were getting really hot. Tested those and found a couple bad the ones that ran the channels with the bad caps and burnt resistors. So i ordered all new D2390 and replaced all off them. Now the unit comes on and stays on for about 15 seconds then shuts off in protect mode.

I am lost on where to go next. Can you guys be of assistance. Thanks

[Jtroutt19]

Re: Harman kardon avr-247

So a small update. I there are two power connections coming from the transformer to the board with the transitors on it. I unplugged both of them and the unit did not shut off so problem is in that board correct? so i plugged one back in. There is a four wire and three wire. I plugged the 3 wire back in. Turned unit on. It sat there for about 3 minutes and then pop! The transistor for the surround left channel blew out but no others these are the ones i replaced. So again i am assuming that the issue lies within that particular channel am i correct?

Now that being said i did not replace the 7 other transistors that are on the board but they tested good.

[tibimakai]

Re: Harman kardon avr-247

You shouldn't replace all capacitors, or transistors.
Measure the final transistors(on heat sink) for short.
When do you find shorted transistors, usually two per channel and most likely both are blown.
Now you know which channel has issue. Since a transistor is blown, most likely that channel is your problem, but I would still check all the channels.
When you have found the bad channel, measure all the components at that channel and replace, what is blown.
If you have idle current adjustment( a little pot on the board, for each channel) pots, you will have to adjust that as well.

[Jtroutt19]

Re: Harman kardon avr-247

Ok I will check tonight the other set of transistors. Why do you say not to replace all caps. I assumed a full replacement of capacity high quality audio caps would be a good thing. There is also the pots for idel current adjustment. What is that procedure for adjusting those?

[Longbow]

Re: Harman kardon avr-247

You have demonstrated the art of the shotgun technique. I used to work with a guy who believed this method was the superior approach. Once - only once - he had a very confusing problem with a HV supply. None of us could make sense of it. Next day the problem was fixed. We all gathered around to find out how the guy figured it out. Well, he didn't figure it out. He pointed to a part he replaced and told us that "it was in stock, so I replaced it". That fixed the problem. Once in a while you get lucky. That's the story.

[Jtroutt19]

Re: Harman kardon avr-247

Lol thats funny...but i didnt just blindly guess here. I saw that caps were swollen and resistors were burnt out. Yes i replaced every cap because i figured since a few were swollen the others would be bad and it had cheap samyoung caps in it. Why not upgrade to high quality caps while in there. After that i tested one row of transistors because i didnt know that both blow if one blows. And i assumed that since i found a couple blown might as well put new ones in there across the board so one is not older than the other.

Now i am on here cause i am trying to learn a better way a more appropiate way a more logical way. You guys are good for that. Not mention you all are more than likely nore experienced than me. I am not a very good diagnostician yet. But i am getting there. I am going to disassembly it again tonight and test the other transistors. I will take and post pictures.

I will ask again how do you properly adjust idle current. And why shouldnt you change every cap if just a few is bad on a board?

When i am doing motherboards or ps boards in tvs i swap all caps out.

[rhomanski]

Re: Harman kardon avr-247

The stuff I work on is very old, 40 years old. So of course I change all capacitors. I think I still would with new stuff simply because they are built so cheap. I replaced one bad cap in a clock radio a couple years ago and six months later another died. I'd probably agree with you on caps but not transistors. Change the bad transistors but leave the good ones unless you know they are failure prone.

[Jtroutt19]

Re: Harman kardon avr-247

40 Years old HUH?! I got an Old tube Radio I am trying to Restore. It works powers on all. But it sat outside in a pole barn for decades. So I have to clean everything up. Some things are going to have to be replaced would it be ok for me to pm you or something if I need any help?

I love old tube radios! I want to make one that shows all the tubes and display them all over my house! I do not know why I am so obsessed with them I just fell in love one day!

[Jtroutt19]

Re: Harman kardon avr-247

This is it. I know it would be easier to just buy a fully working unit but that is not as fun

[rhomanski]

Re: Harman kardon avr-247

I remember them. I had an old Philco years ago, it used an obsolete tube and the books said there was no substitute. I finally found one in a garage in a box of tubes. It hadn't been made since 1962. I paid a dollar for it with high hopes. I plugged it in and turned it on. Started dialing in a station and heard music for about 3 seconds and then it burned out. It had lost it's vacuum I think sitting in that box for years. I had searched for 5 years for that tube. I just smiled and said oh well. Then I tossed it in the trash.

I just finished refurbing an old GE from 1953. It's the same model my Grandfather bought. We got it in 1961 when he passed. My parents used it until about 1968 when a tube went out. My parents threw it out and bought an RCA similar to that one except only AM.

It's not hard to repair them but you need some equipment to align them. They're kind of like a TV, fiddly. You adjust one cap and then you have to go back and adjust the last ones you did again. I sent two solid state ones out for an alignment. The guy said they were way out of alignment, he had to do a full one on them. I thought that's what I was paying for. He didn't see it that way though and got mad.

I'll help if I can, just ask.

[madan1]

Re: Harman kardon avr-247

@Jtroutt19 the odds are that except for the main amp transistors you have at least few other elements blown out. Usually when you remove the shortened elements ( most of the time the two main transistors and the first stage transistors ) the unit will run just fine with the other channels on.
So remove the blown Ts and check if everything else is ok.
Check this video https://www.youtube.com/watch?v=DKCSD3F3D9w