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MCI JH24 head shield issue Recorders, Players & Tape Machines
Old 5 days ago
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analogtodd's Avatar

MCI JH24 head shield issue

I've got an MCI JH24 that isn't doing what its supposed to do!

It looks like a solenoid issue with the head shield... I can't think what else it would be, if anyone has any insight, that would be great.

I'm attaching a video that shows/describes whats going on.

Last edited by analogtodd; 5 days ago at 11:11 PM.. Reason: youtube link
Old 4 days ago
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Radardoug's Avatar

Put your ohmeter on the solenoid, check the coil is there. Check the volts are getting to the solenoid. If it has volts, and the coil is good, it'll be a cleaning problem.
Old 4 days ago
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Also there's a tension screw on the solenoid that provides a drag adjustment. I might be set wrong.

Also, if the plunger is magnetized, it can hang up. In that case, degaussing it might help.
Old 4 days ago
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Richard Crowley's Avatar

The #1 suspect (and the easiest to diagnose) is the coil of the rotary solenoid.
Unplug the solenoid leads and use an ohm-meter to measure the resistance of the coil.
If it is open (infinity) then the solenoid coil is burned out and the solenoid must be replaced.
If the solenoid coil has some reasonable resistance (I would imagine 100s or 1000s of ohms) then maybe a mechanical problem.
If the arm is disconnected from the solenoid, does it operate properly?
It is a pretty good size solenoid, so I would expect that it would have a robust mechanical power.

When you moved the arm by hand, it looked like it was pretty sticky (or maybe that is just normal operation of the dashpot?)
Perhaps the solenoid is trying, but the mechanism doesn't move smoothly.
Do you hear anything from the solenoid? If you touch the side of the solenoid can you feel anything when it gets power?

You mentioned that you had another machine. Is it operable?
When you move the arm by hand, does it feel the same? Looser? Tighter?
Old 2 days ago
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I serviced JH-24's for about 30 years and fixed head shield problems (which were very common on those machines) at least a hundred times but while anything's possible, I don't think I ever had to replace that solenoid. Do the checks that everyone mentioned, which should tell you a lot, and hopefully it's something simple. The problem might also be the solenoid driver board.
Old 1 day ago
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analogtodd's Avatar

Ok, spent some more time on this today...
Demagged it just for fun, no change.
Swapped solenoid driver boards, no change
Tested solenoid, and its getting 22v and it looks like it has resistance, 14ohm (I tested my other JH24 and got the same result, so I assume that must be ok)
Everything for the lifter/head shield comes off J1 on the motherboard, and I've got good continuity, so I don't think its a molex problem.
I did examine and test every component down around the solenoid, the switch, and a couple resistors and a diode, and it all looks like it should.

When hitting buttons like FF where I'd expect some mechanical noise coming from the solenoid, I don't hear ANYTHING, so its not like its stuck and its just not working, its like its not getting logic command, but the logic annunciator looks good. I swapped out logic boards with known good and got the same result.
I'm not sure what else to do....
Old 1 day ago
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Richard Crowley's Avatar

If you take out the three screws and remove the arm from the solenoid and let the solenoid operate by itself?, does it pull-in (and turn)?
It should have quite a kick. Don't get your finger between the disk and the coil, you could lose a fingernail. Or the end of your finger.

It seems odd that one of the three screws is a different kind and looks like it has a hex nut under it.
Is that screw too long? Does it poke down below the solenoid disk and prevent the solenoid from pulling in?

Old 1 day ago
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The one longer screw with the nut is normal. That's the one I mentioned earlier, that is there to add an adjustable amount of drag to the mechanism. When adjusted correctly it prevents the shield from slamming down at the end of its travel. But if it's mis-adjusted it might be causing the solenoid to freeze.

Does the solenoid draw current with voltage present? Does it get warm?
Old 1 day ago
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analogtodd's Avatar

Been running for awhile, the head shield solenoid doesn't feel warm, but the tape lifter solenoid doesn't feel warm either.
Old 18 hours ago
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I would loosen the one long screw and see if it actuates with 22V across the leads. If it doesn't, it's bad.

As further tests you might check to see if it draws current, and see if you can rotate it by hand (which requires some strength), to determine whether it's frozen.
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