kenwood kr-6030 Mosfets?????

[DrDos]

Hello everyone, I have decided to try and replace the mosfets in my power amp (the one with relay and left and right sides) on my kenwood kr-6030. I'm trying to get the A side of my speakers working. I have replaced all the caps in the power board and I thought why not change the mosfets. They seem to be working since I have great music coming out of the B side speakers and since I am not an electronic guru (but I am learning) I don't want to make any mistakes. The mosfets I have are listed A913 so I guess 2sa913 and 2sc1913. Can't really find those in mouser or digikey at least with the info I have but my question is other than knowing wether they are TO92 or TO220 and so forth and also knowing that great voltage can be a good thing, how do I know that the replacements are correct and will work? I don't want to buy from china. There are only 4 replacement numbers to work with. Most have higher collector base and emitter voltage. They are TO220. I know I'm doing the wrong thing by replacing stuff before finding out if its bad and I do not think they are but they look terrible. Should I just pay the higher price for ones that say C1913 and a913??

[Agent24]

If they are working, why do you want to change them?

[DrDos]

because like caps I thought the unit is 50 years old and parts do wear out, however, I thought maybe buy them now and if something happens then I have them.
I also just found out that my schematic has substitutes listed so I don't have to worry any more. I'm also buying new transistors for the output section just in case. Thanks for asking.

[Agent24]

Semiconductors don't usually wear out like capacitors do, but having spares is never a bad idea, of course.
I don't know off the top of my head what would be suitable replacements, however.

But it sounds like both channels are working? So I would leave it alone for now unless it stops working.

Your issues with A/B speaker outputs sound like a switch or wiring issue - if the power amplifier section was bad, none of the speaker outputs would work.
The fact that any outputs work, means the amplifier section works.

Unless you have one working channel and one dead channel, but I think what you're saying is that both channels work, just not on both A and B speaker outputs?

[DrDos]

Yes, I do have one working channel (B) both left and right. My channel A left and right is not working. So, I changed all the caps on the power board that holds the relay and both left and right side speakers. I checked all the little black transistors and the main transistors which all seem to be good. I found one section right next to the relay on both side that had a bad carbon resister so I have ordered that and will replace them. I also installed new caps in the tone board. I wanted to get rid of that old dark brown cap glue which will deteriorate the board over time. I check all the resistors and unless I checked in correctly they appear to be good also. I did not take them off the board to check though because I don't have any artic silver or a new pad to replace and reinstall. J_R from badcaps helped me alot with the wiring of the switch. It didn't look right to me but I did it his way which he said was from the schematic. Anyway yes I get some great classic rock out of this reciever and I'm not even on 1 in volume. Oh, I also shanged the caps on the power board. The only other thing is I don't get stereo (the light doesn't come on and I put new lights in. All the other lamps work. That's it. Got any ideas where I should check next?

[madan1]

Speakers A and speakers B use the same power amp.
If both left and right channels work on either A or B, then the power amp is working.
If only speakers A or B work then look somewhere else for the problem. It is not the power amp, it is not the big caps, it is not the mosfets.

[DrDos]

Okay, what do you call the PCB board that holds the relay and has 2 identical left and right sides on either side of the relay. The schematic calls it a power board. The actual main power board I reallize is not the culprit. I have looked and checked everywhere. All resisteor, tarnsistors with exception to the tuner board. I have only changed one cap on it. I thinkl and I really hate to say it but the switch wiring J_R here gave me might not be right. The jumpers don't look like the schematic. I am waiting on 2 caps to replace in the tone board and then I'm going to change the speaker wiring of the jumpers and fire it up. I expect to get the caps on Monday next. I keep you all informed. I wonder if mylar caps can go bad?

[DrDos]

Let me ask you this: Please look at the schematic on my post before yours. To me according to the schematic it looks like there is a jumper from A- left to B+ left and one from B+ right to A- right. Right now I have a jumper from A- right to B+ right and A- left to B- left. These jumpers are suppose to facilitate the A+B trigger on the switch so I have both A and B speakers working at the same time. Can you tell me if the jumper positioning is currently correct? I just have nothing coming out the A side. Thank you.