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Kenwood Model 500 speaker switch issue

diddlebunk

diddlebunk

Member
Hi all. I was fortunate to pick up a Model 500 in original condition, and just had a local tech rebuild the power supply board and do various maintenance adjustments.

In the course of working on the amp, he found that the speaker selected switch, which isn’t flush with the faceplate, wouldn’t come off. The set screws were replaced at some point by the previous owner (I bought it from his son) with 1.5mm Allen screws. One of them turns just fine, but the other one has no give whatsoever.

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I could make out a bit of blue in the hole, which makes me wonder if Loctite was used. The tech tried some Kroil oil overnight, which didn’t help, and I’ve been putting a drop of acetone in the hole every so often for the past day or so, but there’s been no progress.

The amp functions fine, so the knob sticking out a bit is more a cosmetic issue than anything. Still, it’s prob a matter of time before I’ll need to remove the faceplate someday, and the cosmetic issue bothers me, so I wonder if the community here has any ideas.

Thanks!!
 
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If it is indeed loctite, heat should soften it and allow you to remove the set screw. Heat it up good with a hair dryer (NOT a heat gun!!)
 
Thanks. I was wondering if a hair dryer might help, but I was afraid of possibly damaging the lettering on the faceplate. If that's unlikely, I can give that a shot.

The thing is, even if it's blue Loctite, I still wouldn't expect it to be as stubborn as it is. But maybe the stuff is more secure than I thought.

I really have no idea what the previous owner did — whether he epoxied the knob or whatever — or why he did it.
 
diddlebunk said:
possibly damaging the lettering on the faceplate
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Not too much to worry about on these as the lettering is stamped and filled with paint. If you somehow bugger it up (doubtful with a hair dryer) it's pretty simple to fill it back in.

Another option might be to insert your hex key into the set screw and heat the key with a soldering iron.
 
This problem is out of hand. Loctite this is not.

The blow dryer had no effect, so I contacted EchoWars. He mentioned experiencing something similar with another unit, and he enlisted a machinist to help him remove the screw and rethread the hole.

Well, I just got back from a trip to the local machinist. The screw is no more, and I removed the second one, but the knob still won’t come off. Maybe there’s a shim inside or something? Epoxy?

My next recourse, now that the screws are out, is to hit it again with the hair dryer and see if that loosens whatever else is gluing the knob to the switch shaft.

I’d welcome any other thoughts.

EDIT: Since the screws are out, I think I'll start with a few more drops of acetone down the holes to see if that loosens anything inside. Then I'll hit it with the hair dryer after all the acetone has evaporated.

It has also occurred to me whether or not I should quit while I'm behind. If I do manage to get this knob off, will I be able to secure it properly again? Now I don't know if the set screws were even doing anything.

EDIT 2: This thing will just not budge off of the shaft. If any of you Model 500/600 owners were confronted with this, what would you do?
 
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The tech tried using Kroil oil and I've put Acetone down the drill holes with both screws removed and nothing has changed. A small shot of PB Blaster seems like more of the same?
 
It sounds like epoxy to me, but I hope not. Shear force will be the best method physical method for overcoming it. Options that occur to me:

1. Use as is until a replacement knob is found, then brute force the knob off.

2. Use as is until a replacement knob is found, epoxy a steel bar in the set screw hole and force the knob off.

3. Obtain a replacement speaker switch and cut the shaft on the existing switch and replace the switch wholesale.
 
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Have you tried the two spoon method?. I would use paint tape (a few layers), on the front face and use a pair of the strongest spoons you got. Push on the spoons, close to the knob, otherwise, they will flex too much.
 
It's a tough one w/o knowing why the knob is stuck.

If someone actually epoxied the knob to shaft I would call that a major dumbass move. Heat should soften epoxy as well but it might take more than a hairdryer can deliver. A heat gun can get wicked hot in a hurry and risk damaging the anodizing on the knob, faceplate or both and those parts are virtually irreplaceable .I wouldn't even consider it.

I think a more likely cause is that someone cranked too hard on a setscrew and raised a burr on the aluminum shaft of the switch. Might explain why the knob wasn't fully installed.

You could try - at your own risk - twisting the knob to the stop, and then applying a bit more torque and see if the knob spins even a little on the shaft. If it does, turn the knob to the opposite stop and repeat the procedure until eventually you work the knob free. The risk with this of course is damaging the switch and those don't grow on trees either.

I'd be inclined to live with it as is.
 
Wasn't there someone here on AK that makes nice knob replacements???. In that case, i would go back to a machinist, and have him make a center hole, threadded and, use a screw as a puller. You wouldn't damage the switch or faceplate. These Supremes, have an aluminum chunk, as knobs, therefore, easy to do that way. That screw would push against the switch shaft...
 
turboyam said:
Have you tried the two spoon method?. I would use paint tape (a few layers), on the front face and use a pair of the strongest spoons you got. Push on the spoons, close to the knob, otherwise, they will flex too much.
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I haven't yet. I'd read about that but I'm concerned that such brute force will risk damaging the speaker selector switch or malfunctioning it in some way. But it's something I'm considering.

SPL db said:
Wait, you contacted EchoWars? :idea:
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Great guy. Super patient with a fellow like me approaching him with a random query. Apart from the likelihood of some sort of adhesive, he suspects that burrs on the shaft are complicating things as well.

gort69 said:
If someone actually epoxied the knob to shaft I would call that a major dumbass move. Heat should soften epoxy as well but it might take more than a hairdryer can deliver. A heat gun can get wicked hot in a hurry and risk damaging the anodizing on the knob, faceplate or both and those parts are virtually irreplaceable .I wouldn't even consider it.

I think a more likely cause is that someone cranked too hard on a setscrew and raised a burr on the aluminum shaft of the switch. Might explain why the knob wasn't fully installed.

You could try - at your own risk - twisting the knob to the stop, and then applying a bit more torque and see if the knob spins even a little on the shaft. If it does, turn the knob to the opposite stop and repeat the procedure until eventually you work the knob free. The risk with this of course is damaging the switch and those don't grow on trees either.

I'd be inclined to live with it as is.
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100% agreement on epoxy being a dumbass move — so much so that there's a strong chance it's a burr, as you and EW suggest. Glenn also mentioned the bit about trying extra torque at the extremities if there's some give, but there doesn't really appear to be any. The knob seems to turn very much along with the shaft, there's positively no looseness on the shaft that I can detect.

I don't think I can live with it as is because at this point fixing it has triggered an OCD impulse, and I hate the thought that I can't access the preamp boards if necessary in the future.
 
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