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??

[madan1]

You can check the continuity in the different positions - in position SP A the + terminals for SP A should have continuity to the signal wires and the - to ground. Then on position SP B same but for SP B terminals. In position A+B the signal should go to terminal + on SP A and ground to terminal - on SP B. Terminals SP A - and SP B + should not be connected to anything apart from each other. Basically in position A+B the two sets of speakers are connected in series.



From the schematics, it looks like pins 10 and 4 are shorted between the two plates.

[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.

[DrDos]

This is the board I am talking about. They call it the power board and it might be but I think for the speakers. The one you can see behind it is the tone board. There is a left and right side on it. because the caps are positioned in about the exact same place for both. Other than switch or wiring I just don't know where to look.

[madan1]

Forget about the power board.
The speaker selection happens in lever switch S1 (part number ss33-2034-05). There are at least 2 plates/wafers inside that do the magic. The power switch is also in the same sw itch (I do not understand why tf someone would put mains right next to the speaker outputs, but I guess the japanese engineers know better).

The switch physically must be right behind the power/speaker selector knob.

The board from the attached photo is the power amp board - service manual page 15. The speaker signal then goes to the lever switch. I could not find any good photos of the amp insides, but I guess the board and the switch are connected just by wires. If no one else has been inside the amp, then leave everything as is and focus on the switch. Otherwise you will have a bowl of spaghetti to trace and deal with.

[DrDos]

Well, according to J_R from badcaps the switch is correct. He marked the wires for me and they are where they are supposed to be. He also told me where to run the wires for the speakers. I do that. I think there is a problem with one of the wafers in the switch which I cannot deal with or maybe I just can't find the correct replacement wafers.

[madan1]

You can check the continuity in the different positions - in position SP A the + terminals for SP A should have continuity to the signal wires and the - to ground. Then on position SP B same but for SP B terminals. In position A+B the signal should go to terminal + on SP A and ground to terminal - on SP B. Terminals SP A - and SP B + should not be connected to anything apart from each other. Basically in position A+B the two sets of speakers are connected in series.



From the schematics, it looks like pins 10 and 4 are shorted between the two plates.

[DrDos]

Okay, I think I can handle that. It will take me a while but I will let you know. Thank you very much for the idea I didn't think of it myself.

[DrDos]

WOW! Okay my friend. I think something si wrong. I put the switch in the A position I get per switch pin starting a #1 ground (black wire) =A- right and B+ left and right. On switch pin 2 (gray wire) I get B- Right. Pin 3 is empty. On switch pin 4 (orange) A- right and B+ left. On switch pin 5 (yellow) I get A+ left. Pin 6 and 7 go to lights and power board. On switch switch pin 8 (purple) I get A- and B- Left. pin 9 goes to power board. On switch pin 10 (Green) I get A- right and B+ right and left. On switch pin 11 (blue) I get A+ right. Pin 12 goes to lights and power board. When I say (I get) means I get continuity from the pins to those specific speaker wires. I'll stop here because it doesn't look like the picture you posted. Would you like me to continue with speaker B and A+B settings?

[DrDos]

Alright, lets check the B side: On switch pin 1 (black) I get A- Left and B-Left. On switch pin 2 (gray) I get A- Left and B- Left & Right. On switch pin 4 (orange) I get B+ Left. On switch pin 5 (yellow) I get A+ Left. On switch pin 8 (purple) I get A- Left and B- Left and Right. On switch pin 10 (green) A- Right and B+ Right. On switch pin 11 (blue) I get A+ Right. That's where the continuity goes from the switch. I hope it makes sense to you, because I'm kinda lost.

Now lets check the A + B side: On switch pin 1 (black) I get A- Left and B- Left and B-Right. On switch pin 2 (gray) I get A- Left and B- Left and B-Right. On switch pin 4 (orange) I get B+ Left. On switch pin 5 (yellow) I get A+ Left. On switch pin 8 (Purple) I get A- Left and B- Left and B- Right. On switch pin 10 (green) I get A- Right and B+ Right. On switch pin 11 (blue) I get A+ right. That's it except for phones and I have those too if you like. Please help me to understand this debacle. Thanks.

[DrDos]

let me ask you this, as I see it according to the schematic A- left is jumped to B+ left? and A- right is jumped to B+ right? I believe that is to make the A+B work but maybe I am wrong. It looks like there is a jumper to those wires on the schematic.

[madan1]

let me ask you this, as I see it according to the schematic A- left is jumped to B+ left? and A- right is jumped to B+ right? I believe that is to make the A+B work but maybe I am wrong. It looks like there is a jumper to those wires on the schematic.

Basically in position A+B the two sets of speakers are connected in series.

see the image I attached above, it explains the connection between A and B.

If the schematics do not correspond to what you have, there are the following options:
-the schematics are wrong
-someone has already made modifications/repairs to the unit

It is an old unit, with old and brittle PCBs and parts, if it works - just leave it as is. If you want to get it fully working then you will have to deal with the spaghetti - desolder the switch, check if it switches the correct pins in the different modes and then solder it back according to the schematics.

If you just want to play around with electronics - this unit is a wrong choice. As I mentioned above - it is old, the parts are brittle and you can not buy replacements if something brakes.

[DrDos]

Well, since the colors of the wire do not matter if I follow the schematic and put the jumpers where I think they belong according to the schematic then I should be ok. Apparently there is an incorrect wire I found checking them last night so I will put the wire in the correct place and change the jumpers and then crank it up. I find this 6030 an extremely easy stereo to work on and wouldn't mind working on it all day. I've taken it apart several times and am aware of the pitfalls. I have a call in the Alps to see if they hae old stock wafers for the switch they made for Kenwood but it plays just awesome music I have to get it working. It's something of my generation I could leave to my kid. I expect to recieve the caps I need Monday and then I fire it up and hope everything goes well. Thank you very much for all your help. I dL'd a copy of your post so I would have A, B, A+B pics. Thanks for that. Right now all I can do is try. I opened up a Luxman RX-101 and immediatly tore it apart to sell parts. I'm not working on that and I also tore apart a Panasonix RA-6600. I aint workin on that neither. So, while I have learned alot, at least enough to check caps resisters and other things in the audio stuff I have, I don't think I will be making a carrer out of this. Thanks again. Cheers!