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| | |-+  MCI JH110A Tape lifter Problem
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Author Topic: MCI JH110A Tape lifter Problem  (Read 441 times)
Robomatic
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« on: February 14, 2017, 07:18:54 PM »

Hi. When I'm in fast forward then hit stop the tape lifters immediately drop to heads before the reels slow down. Any ideas on what the problem is? The lifters are supposed to keep the tape off the heads until the reels stop. Rewind function is working correctly.

Thanks,

Rob
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brianroth
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« Reply #1 on: February 15, 2017, 11:28:55 AM »

Hmmmmm....have you tried reseating the analog torque board and the control logic boards?

Bri

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Harrison
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« Reply #2 on: February 17, 2017, 11:12:27 AM »

Also, please check the offsets at the bottom left and right of the analog torque board.
The lifter drops back when the motors stop.
If these offsets are wrong, it thinks the motors are still rotating.
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Robomatic
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« Reply #3 on: February 19, 2017, 08:23:09 PM »

Thanks for the tips guys. I'll try reseating the boards and I'll check the offset and let you know the results. I seem to remember the DC offsets being difficult to null to 0 but I'll slap a meter on them and check again.

Thanks,

Rob
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Robomatic
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« Reply #4 on: February 26, 2017, 09:11:52 PM »

I managed to set the offsets to as close to 0V as possible. Still no change with the fast forward lifters. I'll reseat the analog torque and control logic boards next. Beyond that is there anything else I should be looking at?
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Luddite
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« Reply #5 on: March 01, 2017, 09:40:58 AM »

I've cured analog torque board problems that maddened me for days just by replacing the electrolytics.
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brianroth
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« Reply #6 on: March 01, 2017, 09:17:58 PM »

I managed to set the offsets to as close to 0V as possible. Still no change with the fast forward lifters. I'll reseat the analog torque and control logic boards next. Beyond that is there anything else I should be looking at?

Next step will require an o'scope in order to trace command lines from the "logic" board to the various destinations.  I guess you could struggle through with a meter....


Bri

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Robomatic
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« Reply #7 on: March 07, 2017, 11:40:49 AM »

Ok. Pulled the analog torque board and reseated all the molex with some deoxit. Same problem. Everything else works fine. The DC nulls are at almost absolute O VDC so good there. There are some Fast forward and rewind chips on the control logic board. Do you think the FF chip may have gone wonky?
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brianroth
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« Reply #8 on: March 07, 2017, 03:37:12 PM »

Again, the "correct way" to troubleshoot is to use a scope (or as a last resort, a DVM) to monitor the various control lines in the different modes.  Otherwise, you're just guessing.

Bri

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Harrison
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« Reply #9 on: March 18, 2017, 07:44:41 AM »

How far have you got with this?
The fact that it works one way but not the other is important.
IC 13 and 14 on the torque board develop the +5v signal to tell the logic board that there is still movement, so keep the lifters out please.
The fact that one way, the lifter drops back tells you that the logic board thinks the tape has stopped.
1. Swap IC 13 and 14 on the torque board. the fault might move to rewind.
2. The output of these ICs are limited by a +5v zener arrangement, with a cap across those. See if in FF and RW the motion senses go to +5v. Remember only one of these will go high with direction. ie they both don't go high with spooling.
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Robomatic
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« Reply #10 on: March 27, 2017, 06:21:57 PM »

Thanks for the info. IC 13 & 14 are 741's. I replaced them with new ones and the problem is still there so next I'll check the voltage. Possibly a bad zener or cap?
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Harrison
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« Reply #11 on: March 29, 2017, 07:47:31 AM »

More likely the cap.
If you check the output of IC 13 and 14 in either wind, they will be hard up agains the 15v rails depending on direction. They are in open loop or the later boards have a 1M feedback gain resistor over them.
These feed their relative +5v zener clip for the TTL for the logic board.
In FF you do not get this +5v so the logic board thinks the transport has stopped; Dump lifters.
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Robomatic
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« Reply #12 on: March 29, 2017, 11:06:37 PM »

Thanks for the info. I'll check the caps & the output of the 741's (IC 13 & 14) and let you know if this is the problem.
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