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Kenwood ka7300 Relay stuck on

C

Caron Lyall

New Member
Hello everyone,

This is my first post on AK. I picked up a old Kenwood KA7300 integrated amplifier a couple of days ago.

It has a thump at turn on so I opened it up to have a peek inside, sure enough the relay is stuck on, it never clicks and doesn’t disengage. I tried giving it a few taps but the contacts don’t move.

Checked for DC at speaker terminals
22mv left channel and
62mv right channel at startup, settling down to about
20mv left and 55mv right after about an hour.

Also, speaker a,b and c selector works but not a+b (no output)

Ive cleaned and serviced all switches and pots, all seems to be original inside.

Any ideas or pointers on getting it fixed would be greatly appreciated.

Thank you all :)
 
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Welcome to AK.

DC at the speakers looks fine.

When trying a+b try connecting speakers to both a and b. They could be wired in series.

The relay could be "welded" shut, or maybe someone stuck something in it to hold it closed. Can you tell if the relay has been pulled or opened?

Rob
 
Caron Lyall said:
Hello everyone,

This is my first post on AK. I picked up a old Kenwood KA7300 integrated amplifier a couple of days ago.

It has a thump at turn on so I opened it up to have a peek inside, sure enough the relay is stuck on, it never clicks and doesn’t disengage. I tried giving it a few taps but the contacts don’t move.

Checked for DC at speaker terminals
22mv left channel and
62mv right channel at startup, settling down to about
20mv left and 55mv right after about an hour.

Also, speaker a,b and c selector works but not a+b (no output)

Ive cleaned and serviced all switches and pots, all seems to be original inside.

Any ideas or pointers on getting it fixed would be greatly appreciated.

Thank you all :)
Click to expand...
A couple of things are possible. One like @Robisme said, the relay points are welded together. Another is since A+B isn't functioning, someone could have bypassed the relay and did a "neat" job that looks "original". They could have jumped wires, and/or bridged the solder joints at the relay, or even changed wires at the switch in addition. And if the relay never "clicks", they could have disabled the coil somehow. More investigation, and pictures are needed to get to the bottom of it.
 
If you can get the cover off the relay you can inspect the contacts. A burnishing tool may
clean up pitted or stuck contacts. Skywatcher is correct. Some techs will bypass the contacts of bad relays
with hook up wire to save a repair. Check the foil side of the PC board for jumper wires.
I've also seen small holes burned through the relay cover with a pencil iron so the contacts
can be sprayed.
 
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The reason I didn't believe it was bypassed, is because he stated that the relay contacts never disengage and there is not a click after power up.
This, of course, is assuming the OP knows the engaged and disengaged position of the relay.

OP, you could put a meter across the relay coil and see if you get voltage after the protection delay.

Also, look for bypass jumpers installed across the relay contacts as others have mentioned.

Rob
 
9028C310-8391-4196-BB7A-409A2A07BBEF.jpeg 2A8E79D7-8CF6-40A0-BAA6-0045E460DA93.jpeg 14E12290-F5D7-48D3-B138-3CCF2F0C65CE.jpeg 0D068E93-CEF8-4F2E-90B5-1F85D0CA7F59.jpeg 9028C310-8391-4196-BB7A-409A2A07BBEF.jpeg Thank you everyone for the tips. I disassembled the relay today and took some photos. The relay is not stuck but rather the spring pulls the bottom of the contact switch “up” thus making the switch “dip” at the front and make contact with the bottom connectors if that makes sense. Please see the photos for reference.

The moving part of the relay never moves up to disengage, it doesn’t seem to be touching anything, it pivots up and down freely but the spring makes it contact the bottom connectors which is why it’s always “on”.

Also noticed a bit of heat damage on the board, the two green resistors get very hot and I’ve had to re solder some points as the old solder just crumbled and fell off .

Not sure if the whole board needs a rebuild or if it is just a buggered relay.9028C310-8391-4196-BB7A-409A2A07BBEF.jpeg2A8E79D7-8CF6-40A0-BAA6-0045E460DA93.jpeg14E12290-F5D7-48D3-B138-3CCF2F0C65CE.jpeg
 
Skywatcher said:
A couple of things are possible. One like @Robisme said, the relay points are welded together. Another is since A+B isn't functioning, someone could have bypassed the relay and did a "neat" job that looks "original". They could have jumped wires, and/or bridged the solder joints at the relay, or even changed wires at the switch in addition. And if the relay never "clicks", they could have disabled the coil somehow. More investigation, and pictures are needed to get to the bottom of it.
Click to expand...

Second update:
I think you may be right. I just thought I’d manually trigger the relay and sure enough it never disengages no matter position the switches are in, so I’m guessing it has been somehow bypassed. I can’t see anywhere on the board itself but then again I’m no expert.
 
Caron Lyall said:
View attachment 2111964 View attachment 2111965 View attachment 2111966 View attachment 2111967 View attachment 2111964 Thank you everyone for the tips. I disassembled the relay today and took some photos. The relay is not stuck but rather the spring pulls the bottom of the contact switch “up” thus making the switch “dip” at the front and make contact with the bottom connectors if that makes sense. Please see the photos for reference.

The moving part of the relay never moves up to disengage, it doesn’t seem to be touching anything, it pivots up and down freely but the spring makes it contact the bottom connectors which is why it’s always “on”.

Also noticed a bit of heat damage on the board, the two green resistors get very hot and I’ve had to re solder some points as the old solder just crumbled and fell off .

Not sure if the whole board needs a rebuild or if it is just a buggered relay.View attachment 2111964View attachment 2111965View attachment 2111966
Click to expand...
You have quite the mess there. I can see multiple problems. One is the glue has corroded some things. And those 470uf grey caps might be leaking their electrolyte. The tell-tale sign is the traces are turning black under the (what was) green, and the electrolyte rots solder and makes it crumble like dried mud. I just got done repairing an H/K with physically leaking caps that rotted the solder and traces. I think you might want to be prepared for some serious work. I had scraped the green from the affected traces and the copper was all corroded and pitted. I cleaned them as best I could, fluxed then tinned them with solder, and added pieces of trimmed leads soldered to the traces to reconnect everything so they were solid. Then coated everything with corona dope to seal them. It takes a while and lots of patience. You have to stop the corrosion so it stops spreading like a cancer. Then you'll have to figure out where the relay has been bypassed and reconnect everything to where it belongs. And figure out why the relay doesn't work. It should click no matter what if the protection circuit is working.
 
Skywatcher said:
You have quite the mess there. I can see multiple problems. One is the glue has corroded some things. And those 470uf grey caps might be leaking their electrolyte. The tell-tale sign is the traces are turning black under the (what was) green, and the electrolyte rots solder and makes it crumble like dried mud. I just got done repairing an H/K with physically leaking caps that rotted the solder and traces. I think you might want to be prepared for some serious work. I had scraped the green from the affected traces and the copper was all corroded and pitted. I cleaned them as best I could, fluxed then tinned them with solder, and added pieces of trimmed leads soldered to the traces to reconnect everything so they were solid. Then coated everything with corona dope to seal them. It takes a while and lots of patience. You have to stop the corrosion so it stops spreading like a cancer. Then you'll have to figure out where the relay has been bypassed and reconnect everything to where it belongs. And figure out why the relay doesn't work. It should click no matter what if the protection circuit is working.
Click to expand...

Thank you for your advise. I’m still learning and can do basic troubleshooting but had no idea about the glue and corrosion. I might put it back together and take it to a tech and get it professionally checked out. Not too keen on taking on such a repair.

The relay never moves, and there is sound at the speaker outputs no matter what position the relay is in (I tried moving it up and down manually)
 
Caron Lyall said:
Thank you for your advise. I’m still learning and can do basic troubleshooting but had no idea about the glue and corrosion. I might put it back together and take it to a tech and get it professionally checked out. Not too keen on taking on such a repair.

The relay never moves, and there is sound at the speaker outputs no matter what position the relay is in (I tried moving it up and down manually)
Click to expand...
Where are you located? Perhaps someone knows of a good honest tech close enough to you.
 
I do not agree with the leaking caps or the glue being an issue. I would remove the caps and get some acetone and clean the board on both sides. I just recapped one of these and I tested the caps the Gray Elana caps were surprising in spec. Not saying I would not replace them but they were not leaking.
The grey / black caps can be replaced with a nichion UPW cap the orange needs a UKL

The discoloring is from the diodes and how hot they get not from glue
 
Just a follow up on this protection relay fault. I took a look at it for Caron Lyall. The relay had indeed been bypassed, via bridging the pins on the pcb (18-19,20-21) A few caps and out of spec / burned resistors replaced, and now the relay is working how its supposed to. The Ck7 10µf cap, under the Zener diodes had failed completely and was really the only component stopping it from functioning. Somebody in the past was very lazy when they went and bypassed the relay this way.

IMG_20210321_210849.jpg
Blue / Yellow wire pins...
 
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