Kenwood KR-5030 Power Switch Repair

[Spenser]

Hi everyone. Hope this finds you well.

Next up is a Kenwood KR-5030. The machine seemed like it could be suffering from classic 'power-switch-eye-tis'. That is not what's wrong -- I think -- now that I've begun to take a peak.

(EDIT: We shall find I was mistaken. Power switch failure IS exactly what was wrong.)

I've cleaned up the contacts in the power switch. There definately was a good bit of carbon build up on the contacts and a little arc residue on the interior switch housing. Also cleaned mains fuse holders and fuses.

Still fizzling horribly. Dial lamps flickering like mad. Good news is, we are getting enough juice to activate the relay. But I'm afraid to leave the receiver turned on for very long. Fizzling sound sounds like it is coming from vicinity of the power supply slash transformer area.

What do I have here; a bad safety cap Ck1 0.01uF 125V? Other possibilities that should be dogged down? Recommended next steps; test(s); substitution component(s); cautions?

After I fix what's wrong with it I DO plan on doing thyristor / power-switch-modification, AND a restore, assuming nothing so major it should be parted out.

Thanks!

 

[gort69]

I'd still guess it's the power switch. You can jumper across the contacts at he switch to test. 16 AWG ought to be fine.

 

[Spenser]

Bingo. That worked.

Thank you!

I'm thinking now, with a cleaned-up switch, there will be enough current to trip a thyristor yes?

 

[gort69]

Is there an unused pair of contacts as in the KR-4070? Same basic deal I'd think but have never had one.

 

[Spenser]

There is no set of unused contacts as in the KR-4070.

Idea is thyristor in a heat-sinked position and a 100 Ohm 1/2 watt resistor.

I gotta hit the hay. Thanks again!

576-Q4025L6

http://www.audiokarma.org/forums/in...orth-5-and-an-hour-or-so-of-your-time.504673/

 

[quaddriver]

thyroid or not, Id feel better if the switch was all there....is it the rough same size and shape of the dual side 3090/4070 switch? If so, auntie em might have one in barter town.

 

[gort69]

There's a NOS one on the bay for a 4070 - ad states it also fits a 5030. Search Alps SDR3R No affiliation

 

[Spenser]

Nice find on ebay. The 5030 uses the one-sided kind -- but the replacement you found (two-sided), would probably work even better. Run the current through both sides of the double switch and half the load for each.

$35 though. IDK. I've already got the thyristor and it was $3 and 31 cents.

There is a lot of metal left on both sides of the set of points in the switch. It is just that the two surfaces no longer mate like they once did. Haha. All it needs to do is be able to nicely conduct say 120mA -- I think. I'm going to see if the old switch will work with the modification.

Ck1 stays, right? I believe there is no RC filter, in this case, that should be removed.

Thanks.

 

[Spenser]

OK thyristor and resistor installed. No more flickering indicator lamps. Still some now-quieter sizzling. IDK. Sizzling stopped after awhile. I think. Must run receiver some more and see. Can detect ever-so-slight slight normal transformer hum, Only thing general-operation-tested so far was FM stereo and mono tuner modes under set of speakers. Works. Sounds pretty good right out of the the gate. Needs a good cleaning.

 

[Spenser]

Took the power switch back out and apart again. Folded a little piece of fine grit sandpaper back on itself so it became two-sided. Placed that between the contacts of the switch in the closed, "on" position, and worked the sandpaper back and forth gently a few times. Reassembled the switch. (One of our contributors in the thread linked on Post #5 said a bit of a rough surface actually helps make for more effective contact.) In any event it seems to have worked. No sizzle in the half dozen times I tested it. Time will tell.

 

[hopjohn]

is foating in space in the area of the power supply board attached to a small, aluminum, finned, independent heat sink. Mica insulator.

The thyristor has an isolated tab so why the mica? ... and why not just mount it to the chassis somewhere instead of the added heatsink? and why is that chunk of aluminum flopping all around the power supply just waiting to short something? I don't mean to be harsh, and maybe you have further plans, but from what I can see it currently appears unnecessarily dangerous.

 

[Spenser]

Hi Hopjohn. Oh my gosh. You are right. I was thinking those thoughts but pressed on -- kind of goofing around. To make matters worse, even just TO GIVE THE IDEA that ANYTHING could be left flopping around as a finished modification like that -- seriously -- could lead to someone setting up a potential disaster. Good grief. I am a menace. I'm glad you said something. I need to mend my ways.Post #10 and 11 should be edited to strip out the temporary insanity. I will repost when thyristor is in place.

What spec wire works for the hot wires?

While I've got you, would this receiver benefit measurably from a recap? It is in very good shape cosmetically and sounds good.


Thanks.

 

[hopjohn]

What spec wire works for the hot wires?

The wires that go from the alternistor triac thyristor "thyroid" to the switch don't need to be very large, 22-24 gauge will do. I reuse (leave them in place) the stock wires that were originally on the switch that go to the transformer (load) and hot. I think those are 20 gauge usually

While I've got you, would this receiver benefit measurably from a recap? It is in very good shape cosmetically and sounds good.

It appears to be a pretty simple recap. There's no money in it if you're gonna flip it, but if for a fun project you intend to use, then go for it. I redid my KR-4070 if that says anything. These receivers aren't the best built, but they sound surprisingly good if you're not trying to knock the walls down.
.

 

[Spenser]

Thanks. I, too, reused the old hot and load wires. I used 22-gauge wire to connect the old switch to the thyristor G terminal (with the 100 Ohm 1/2 watt resistor). I used 20-gauge wire to the switched external AC power outlet.

Placed thyristor on the chassis around midships.

Adjusted bias.

Thanks also Hopjohn for your wisdom on receiver recap in this case. I like it a lot. Probably going to send it on down the road, though. IDK. I'm going to get a Kenwood KR-4600 onto the bench here shortly and take a look at it. Might hold onto one or the other for awhile.

 

[Spenser]

Thyristor Solid State Switch Modification Kenwood KR-5030

 

[quaddriver]

Thanks. I, too, reused the old hot and load wires. I used 22-gauge wire to connect the old switch to the thyristor G terminal (with the 100 Ohm 1/2 watt resistor). I used 20-gauge wire to the switched external AC power outlet.

Placed thyristor on the chassis around midships.

Adjusted bias.

Thanks also Hopjohn for your wisdom on receiver recap in this case. I like it a lot. Probably going to send it on down the road, though. IDK. I'm going to get a Kenwood KR-4600 onto the bench here shortly and take a look at it. Might hold onto one or the other for awhile.

and if it dont work, I need the knobs off the 4600 for one I have...

 

[quaddriver]

btw - when doing switch contacts, they need to be rounded, convex is the word, when flat, they eventually pit the center and dont contact. use a nail file, just like your wife has, to re-round them.

 

[Spenser]

OK. Thanks. Good to know.

 

[Mantolaman]

I think the KR 5010 I just got has the same symptoms. Lights flicker when first turned on. But relay always clicks in, and the unit performs well on both channels. Occasionally the light don't flicker but do most of the time, (when turned on).
So far, I have both top and bottom covers off, blown out dust, which was not bad at all, Deoxit on the switches. Checked the offset and adjusted to zero.
Other than being able to check some voltages that's about the extent of my ability to diagnose problems.

I'd like to try and install the mentioned thyristor as shown in post #16, but not sure I'm able. I'm hoping the work I've done so far eliminates the problem, but sounds like the modification would be good insurance.

Would be nice to see some detailed information on how to install the thyristor.

 

[Spenser]

It's all here. You'll have to deduce the specific plan or ask specific questions. Personally I'm sort of on leave from Audiokarma on HF radio stuff and only checking in or applying time here sporadical like.