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MCI jh 16 problems... any thoughts?
Old 17th May 2006
Gear Nut
🎧 15 years
Question MCI jh 16 problems... any thoughts?

alright folks, first let me thank you for having a look and throwing ideas my way

i just bought a '79 mci jh16 as a fixer project. and my first issue is..... the transport. big supprise eh?
when i power up the machine the transport doesnt turn on (no lights on buttons, no funtionality at all). and the motors start spinning at full rpm. the transport doesnt work on either the deck or the locater. i figure my first step is to get this to turn some tape, and then take it fromm therre.. thanks everyone
Old 17th May 2006
Lives for gear
axisdreamer's Avatar
🎧 15 years
I have an JH16 wide body deck as well and it has some problems yet.
Do you have the tech manual for it?
I just saw the tech manual today on ebay for sale if you need one.

I'm not much of a tech so I won't be much help.I do have some extra cards if you ever need any,also are your cards like the old ampex? Thats what mine are,just like the ampex 440 and mm1200.

good luck!
Old 17th May 2006 | Show parent
Lives for gear
🎧 10 years
I believe the JH-16 uses the JH-10 transport, which is all AC motors, with 24VDC relays doing most of the logic. I have done a lot of work on them and they can be a real bear. You won't get anywhere without the schematics. I do have a set. First thing I would do would be to check and make sure all the relays are fully seated in the sockets. Then you need to verify whether the voltages are there. There should be a couple lights on the deck, close to the tape path, with an LDR(with a heatschrink hood). If those lights are off, then the transport thinks that tape is in the path and will apply tension voltage to the motors. Good luck!
Old 17th May 2006 | Show parent
Gear Nut
🎧 15 years
thanks for the replies thus far...
my jh-16 is a 79. so it doesnt use the old school relays and photo sensors like the older versions.. it looks almost ident to the jh-24.. it has the 114 transport and the card draws.
Old 18th May 2006 | Show parent
Lives for gear
brianroth's Avatar
🎧 15 years
Reels running at full-tilt would be shorted power transistors in the Motor Drive Amp in most cases.

The JH-16 and JH-24 transports were almost identical, FWIW.

Old 18th May 2006 | Show parent
Lives for gear
🎧 10 years
That transport is about the same as the JH110, which is DC motors and TTL logic. MDA's could be bad. Something dead on the TTL logic circuits. You need the schematics to track things down. Checking for dead transistors on the MDA's shouldn't be hard.
Old 23rd March 2016
Here for the gear
🎧 5 years
Hello! Hoping to restart this thread with some people who know about JH16 machines.

I have a JH-16 with a JH100 transport. The transport has no movement. It died when the Supply reel started slowing down and made a strange straining noise. I've replaced voltage regulators on either side of the motherboard chassis. I've recapped the power supplies and analog torque board. Before I did all of this I had a molex plug 1 pin off and I burned an IC on the torque board. I replaced all parts nearby including the sockets and the ICs /resistors/transistors nearby. I have no red sockets. I must have burned the supply motor too as I had a tech come in and find out the motor was fried, so I had it rebuilt. I've also replaced some funky voltage regulators in the transport power supply. Still no luck.

I've reflown the entire mother board, recapped the mother board (a couple electrolytics and the string of 0.01uf ceramics along the bottom) and I'm getting proper voltages all along the motherboard, all within 1V variance of specified voltages. When I have daughter boards connected I find proper voltages on all test points and connection pins to the PCBs.

EXCEPT for one of the small PCBs that control solenoids. I have no schematics for these identicle PCBs but 4/5 have exactly the same voltages going to the same pins, and the one controlling a "Z Roller" is different. I can't figure out what a "Z Roller is...

Most of the lights (RW,FW, PLAY, REC, SHEILD, but not EDIT) work, the shield, and the capstan and pinch roller seem to function perfectly, maintaining pressure and varying speed according to 15/30 ips, and along with the varispeed knob. I've had the remote unplugged since the trouble started to make sure it wasn't something in there.

The only strange bits of functionality I can figure out is that the transport does not respond to anything at all - no idle, no movement, and the tape sensor takes a few tries before it releases the brake (though it lowers the shield 1st try every time)... as in I have to trigger it 3-4 times before the solenoid fully engages, but I can hear it trying each time I trigger the sensor.


What's a Z Roller?

does anybody have any clue what could be going on with this machine?

below is a photo showing the PCB layout with the "Z Roller" solenoid board

View image: Screen Shot 2016 03 23 at 4 49 37 PM
Old 25th March 2016
Lives for gear
🎧 15 years
The Z (impedance) roller was a damped roller on the supply side of the deck meant to improve flutter. A solenoid causes it to engage in play and record modes, but disengages the roller (allowing it to spin freely) in fast wind modes. I doubt that that part of the machine is your problem.

There may be multiple issues going on and perhaps some are new, caused by the work recently done. With all that reflowing and recapping and no way to check for new issues as you went along, it would be easy to introduce a new fault or two.

Very hard to diagnose this from afar, and it could be many different things. You might check for a stuck stop switch, The machine shouldn't act different with the remote unplugged; if it does that points to a fault in the remote or cable. The microswitch in the tape lifter circuit can also cause weird transport problems if it isn't mechanically actuating the way it should, or if the switch itself is faulty. Obviously, a bad transport supply could cause these problems too, or something in the control logic or torque boards. Do the turntables spin freely with tape threaded and do the brake solenoids turn on and off when they should?

Make sure that ALL the power supply voltages are present, on all the major PC boards. After that, at the servo test points on the analog torque board in fast wind modes. Basically, if the servo circuit sees that a fast wind mode is selected but the reel motors are not spinning, it will send high DC voltages to the transport supply to get them moving. If you do see those DC voltages, that means the logic circuits are doing their job but the transport supply isn't responding. Conversely, if you don't, that means that the control circuits have some malfunction. This test can at least tell you whether to focus on the control circuits or on the transport supply.

Also, you can the blocking the tape sensor, unplugging the reel motors, and pressing play. In that state the pinch roller solenoid should kick in and the capstan motor should turn. If neither of those things happen, look more closely at the control circuits.

To unravel this stuff it's really best to pull out the schematics and trace the control signals, step by step, from the logic board to the motors. Many symptoms appear in your case but you can just pick any one signal and trace it through. If you can understand the schematics and do that step by step, it will lead you to the fault, or at least one of them. But you need to understand how the logic of the machine really works, and have the knowledge and patience to follow those signals inch by inch through the molexes, motherboard, and PCB components, to properly fault find. Good luck with that beast!

Last edited by David Kulka; 25th March 2016 at 05:52 PM..
Old 25th March 2016
Here for the gear
🎧 5 years
Hey Dave,

I don't think the stop switch is stuck, as the capstan starts spinning when I press play and stops when I press stop. I unplugged the remote not because I was getting varied behaviour, but just to cut down on the potential variables.

The turntables spin freely with tape threaded (though like I said in the previous post, I have to trip the sensor a few times before the brake solenoid fully disengages the brake) and when I remove the tape from the sensor the brake solenoid engages the brake (always does this 1st time) and stops the turntables from moving.

I checked most major PC voltages - Torque board, Phase Lock, Lamp driver - and they appear fine. I have schematics for the deck but don't have voltages for the Logic board (just have an IC diagram) or the Solenoid boards so I had nothing to compare readings to.

With the tape sensor blocked I have the same functionality when the reel motors are plugged in or unplugged - i.e. the capstan will spin when I press play and the pinch roller pinches in both cases.

The tape lifter also seems to be engaging properly as when I press the FFW or RW buttons the lifter comes out and the shields go down. In these modes the capstan also stops and pinch roller disengages.. just no transport movement.

Thanks for you help! You're right though I think the best way to diagnose this problem is tracing back the circuit, I'm just in way over my head at this point. To make matters worse I shorted out two connections in the main supply plug (J1) and now the thing is blowing the 5A main deck fuse whenever I turn it on.. So i can't check the servo test points in FF as you suggested.

Anyway.. I think it's time to call back the tech.
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