KR-4070 switch fix with triac.

hopjohn

Silver Face
I'm not going to go through the whole triac install procedure again. If you want a good tutorial on that you can go view it in my KA-9100 thread posts #82 and #83. This is just to give an idea of how it can be done in the KR-4070 which has the infamously failure prone power / speaker selector switch.

To get the switch removed disconnect the large molex connector behind the switch. Then remove the metal rod that goes through the center of the switch and contact wafer by simply pulling it out the back. Then use a flat blade screwdriver or the like to open up the tabs on either side of the switch and remove the gray plastic switch housing. The two halves of the housing are just friction fit and pull apart to reveal the contacts inside.

My switch contacts were not all that badly pitted compared to others I've seen.
i2Sc9LO.jpg

cZfeFeF.jpg


Once cleaned with some DeOxit D100L & G100L
pZqKg3R.jpg


DKJ5Sqh.jpg


In order to bridge the top and bottom contacts I soldered on the bottom leads first and routed them through the gap at the bottom. Then insert the switch housing back into the switch body and retighten the tabs.
cdIfiKA.jpg

tIOzOmE.jpg


The triac (thyristor) can be mounted conveniently atop the heatsink in the preexisting hole with a M3 self tapping screw.
iGpGXn3.jpg
 
Did you experience an increased hum of the power transformer after installing the Triac switch? I've done this mod to several of my units, but the last one I did (Yamaha CA-810) suffers a hum of the power transformer. Very odd.
 
No, I did not. I have heard the complaint before, but I've never run into that issue having performed this mod many times.
 
Hey All,

I own a kenwood kr 6050. I've cleaned the contacts in the power switch, and it's firing up fine at the moment, but I know the switch is doomed to fail again. Can I attach the triac directly to the heatsink on the kr 6050 as well? I've read that I need to use some type of washer between the heatsink and the triac if I do. Is that true? This post hasn't had activity in two years so fingers crossed someone will chime in!
 
I'm not familiar enough with the 6050 to answer about mounting locations. Provide photos for further assistance in that regard. The triac part I used has an isolated tab (not all of them do), so it is not electrically active allowing you to mount it without any external isolation required.
 
I'm not familiar enough with the 6050 to answer about mounting locations. Provide photos for further assistance in that regard. The triac part I used has an isolated tab (not all of them do), so it is not electrically active allowing you to mount it without any external isolation required.
Thanks for the reply, hopjohn! I'll post pics once the triac arrives and I open the kenwood up again. Fingers crossed the triac I ordered also has an isolated tab. The proximity of the heatsink to the power switch seems almost identical in my kr 6050 as it is in the kr 4070.

I'd like to take this project on myself, but I'm concerned that I won't wire it correctly. I've looked at various diagrams in many of your and other posts to try to make heads or tails of it. But looking at it on paper is a bit confusing to my neanderthal brain. I'm hoping once the triac arrives, and I can look at the labels on it, and identify with a multimeter what the hot wire in my kenwood is, that this will make more sense.
 
Working on a 4070 with the same switch problem. Pictures are a tremendous help. Searching on google I read some use the points not used and swap them. Thanks again for pictures.
 
FWIW - the original switch for the 4070 only had one set of contacts. The replacement switches from Kenwood had 2 sets of contacts. There were no instructions, but Kenwood repair people told us (warranty station at the time) to parallel the pairs of contacts, which greatly extends life. Uninformed techs would just connect one set, so you see a lot with just the one set connected. Also, if the contacts aren't too pitted, sometimes can improve performance by decreasing gap between contacts. Nice pictures and thread...
 
I opened the switch on this one and it does have 2 sets of contacts, one pair not used. If I had known it I would not have opened it but just turned it around. One clue of which one you have, my switch has solder tabs on top and bottom, bottom ones not used. I will assume the one set of contacts switch will not have but one set of solder pins.
 
...I've done this mod to several of my units, but the last one I did (Yamaha CA-810) suffers a hum of the power transformer. Very odd.

I also had an issue with the CA-810. It wasn’t a hum, but an odd, occasional pulsing of the meter LEDs I tried to connect the gate to M1, but no improvement. I’ll probably switch to a relay if I can find room. Worked perfectly on my KA-6004.
 
I'm not going to go through the whole triac install procedure again. If you want a good tutorial on that you can go view it in my KA-9100 thread posts #82 and #83. This is just to give an idea of how it can be done in the KR-4070 which has the infamously failure prone power / speaker selector switch.

To get the switch removed disconnect the large molex connector behind the switch. Then remove the metal rod that goes through the center of the switch and contact wafer by simply pulling it out the back. Then use a flat blade screwdriver or the like to open up the tabs on either side of the switch and remove the gray plastic switch housing. The two halves of the housing are just friction fit and pull apart to reveal the contacts inside.

My switch contacts were not all that badly pitted compared to others I've seen.
i2Sc9LO.jpg

cZfeFeF.jpg


Once cleaned with some DeOxit D100L & G100L
pZqKg3R.jpg


DKJ5Sqh.jpg


In order to bridge the top and bottom contacts I soldered on the bottom leads first and routed them through the gap at the bottom. Then insert the switch housing back into the switch body and retighten the tabs.
cdIfiKA.jpg

tIOzOmE.jpg


The triac (thyristor) can be mounted conveniently atop the heatsink in the preexisting hole with a M3 self tapping screw.
iGpGXn3.jpg
Hi, can you jumper the pins of the harness plug to bypass the switch for testing purposes? Bought a totally dead 4070. Power going to switch. Want to temporarily bypass switch to see if that is the issue.
 
The switch can be bypassed for testing, but some other means of switching power will be necessary, and a DBT for protection seems like nearlty a necessity with an unknown DOA unit. Something took out the switch contacts, after all.
 
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