Any MCI tape machine users here?

  • Thread starter Thread starter briank
  • Start date Start date
Went to take some measurements on the PLL and swap a couple ICs in the AT board but today the left reel has decided not to work in play/rec either...this "moving target" stuff is bugging me out. This machine is mocking me!! :spank: :D


So symptom sit-rep today:

With card in tape sensor slot, no tape loaded (since it will just dump on the floor):

-both reels idle fine; both can be trimmed to the correct 3 revs per second idle

-FF and REW: function fine--left reel spins in RW and right reel spins in FF; tape lifter function as they should

-PLAY and PLAY/REC: light up; the capstan spins fine but neither reel spins now (for the last couple weeks up until today it was only the right reel that didn't work in play; a few weeks ago both reel motors spun in play although tension was too low on right side)

-STOP: stops the capstan from play; slows and stops reels from FW/RW

-EDIT: lights up; stops both reels idling

PLL gain should be ok; showing 19.2k/9.6k/4.8k at 30/15/7.5ips; 5v/22v ok; tried checking the ICs and testpoint waveforms per the PLL troubleshooting section of the manual; voltages are correct with a card in the slot in play at 15ips but I can't load tape since the reels won't turn in play now.

In summary: yesterday the machine had a good hair day; today, not such a good hair day. This is agony!
 
OK, sorry for the millionth post but made some headway today...I reckon I'm having contact problems...the scoop is...as far as I understand it, I should be getting 5v from the control logic to pin 6 on P14 on the analog torque board (it's related to the right play functionality) and have been advised that getting less voltage than that would cause reels to not function in play...but I was only measuring 3.20v at that pin...sooo...I pulled the control logic board, resoldered the molexes on it, cleaned some pins, and no change (but at least it's resoldered now :D )...so...traced around a bit and wound up pulling the PLL board and here's where things got interesting. I resoldered the pins on P44, and also took a pencil eraser and cleaned up the pins and traces around J44 which is what P44 connects to on the motherboard. After this, I fired up the machine, stuck a card in the tape sensor, hit play and bingo...the right reel spun...for about 5 seconds or so...and pin 6 on P14 now measures 3.25v...not a big difference, but it was enough to suggest that I have some dirty traces, grumpy molexes and basically lots of cleaning and re-soldering to do...

NOW maybe I'm barkin' up the right tree? :p
 
You know what MCI stands for, right?

Munchy
Crunchy
Intermittencies

ah well. Good luck with tracking this one down. Sorry it's a headache.
 
THis sounds better and on the right track.

+5 is the TTL logic supply rail and 3.2 volts should be enough to switch the 7426. But you should check that. The 7426 is open collector which means that there is just a transistor collector on the output. If the output transistor is on then the transistor grounds the output pin. If the output transister id off then the output pin floats up to whatever voltage the the pull up resistor is connected to. In this case +15. So you can take a look at all the inputs to find out if they are logic high or logic low and then take a look at the respective output pins to see if they are (near) zero or up near +15. The nand gate is acting as an inverter. Logic high in, ground the output.

One thing I have seen in older TTL logic like this is a failure mode where the open collector output does not pull close enough to ground. If this is the case then replacing the 7426 would help.

On my JH-110A IC 24 pin 11 is 14.65 in stop and 0.42 volts in play.

Regards, Ethan
 
evm1024 said:
THis sounds better and on the right track.

+5 is the TTL logic supply rail and 3.2 volts should be enough to switch the 7426. But you should check that. The 7426 is open collector which means that there is just a transistor collector on the output. If the output transistor is on then the transistor grounds the output pin. If the output transister id off then the output pin floats up to whatever voltage the the pull up resistor is connected to. In this case +15. So you can take a look at all the inputs to find out if they are logic high or logic low and then take a look at the respective output pins to see if they are (near) zero or up near +15. The nand gate is acting as an inverter. Logic high in, ground the output.

One thing I have seen in older TTL logic like this is a failure mode where the open collector output does not pull close enough to ground. If this is the case then replacing the 7426 would help.

On my JH-110A IC 24 pin 11 is 14.65 in stop and 0.42 volts in play.

Regards, Ethan
Click to expand...

Thanks again, Ethan! I'll check these out-
 
evm1024 said:
THis sounds better and on the right track.

One thing I have seen in older TTL logic like this is a failure mode where the open collector output does not pull close enough to ground. If this is the case then replacing the 7426 would help.

On my JH-110A IC 24 pin 11 is 14.65 in stop and 0.42 volts in play.

Regards, Ethan
Click to expand...


Been a couple days since I checked it, but at IC 24 pin 11 if I recall right I was getting about 14.75 in stop and 0.06 in play.

I pulled this puppy apart, resoldered and cleaned all the Molexes on the motherboard, all daughter cards (including the motor driver board in the chimney), and it didn't change anything, the symptoms remain...aw raspberries...but at least I know all that stuff is re-soldered and spic and span now :p

I guess I'll swap 24 with its counterpart on the other side (18 IIRC) and see what happens?
 
No need to swap IC 24. You are getting the correct signal. The signal from IC24 pin 11 is used to turn on the FET in IC25....

I recall that your deck FF and REW ok and that you have adjusted idle tensions. Is that correct? If FF works correctly then IC26 and IC27 annd all downstream motor driver parts are working. In addition IC25 fet #1 (14 in 16 out) is working (this passes the FF signal to the driver).

Next step is to work upstream from IC25 fet #2 (pins 3 and 1) to be sure that the signal is passing through.

So, when in play IC24 pin 11 turn on IC25 FET #2 which will pass the play torque signal. The first check is to verify that in play mode (no need for tape just use a card) that the signal voltage at IC25 pin 1 is the same as IC25 pin 3. Might want to scope them in DC mode. If they are significantly different them IC25 is bad. If OK then we need to look further up stream.

IC25 pin 3 is driven from IC12. IC 12 pin 3 should be the same signal as IC12 pin2 except that its sign is inverted. (+1V in = -1V out) If this is not the case then IC12 is bad.

R41 sets the right tension and "shouuld" have been adjusted somewhere along the line. If not then you should try adjusting R41 more clockwise to see if you get reel motion. If not then we need to look at IC7 and its circuits.

My analog torque board has a test switch. It appears that yours does not. Too bad. I'll see if I can measure some voltages on my deck in play mode so that you will have something to compare against.

Do I recall that you swapped IC7 and IC3?

Regards, Ethan
 
evm1024 said:
I recall that your deck FF and REW ok and that you have adjusted idle tensions. Is that correct?
Click to expand...

That's correct-


Do I recall that you swapped IC7 and IC3?

Regards, Ethan
Click to expand...

Sure did, and no change to symptoms.


Thankyou thankyou thanks again, Ethan! I'll go and test the pins you suggested. If you have a chance to give me those reference measurements, that would be huge of you once again. Otherwise, I'll check these out and report back. Can't thank you enough, Ethan!
 
Briank

I've been looking at this post every so often and not really in detail. Whenever I had a problem I always checked the four transistors (in the power supply) and make sure you're getting the -18/+18v's and the +15/-15v's. It's located at the front of the PS. Then I would check the chimney transistors and make sure your voltages are above 5v's. If anything every went quirky (work/not work) and because the voltages were off. Mind you, the other stuff you are doing has to be correct also. But starting at the source would be a start. If you're not getting those voltages the transistors are going south and need to be replaced, so matter how much soldering,etc, may not help. Like I said, I haven't read this in detail.

Mine did that and even after having replaced them, two weeks later they went out. My 2 cents, learned from Steve. I've always either had to replace the IC's or the transistors.....

Good luck,

John
 
Always a good idea to check the supply rails. You can measure it on the 741 opamps on the analog torque board. Pin 7 is the +15 rail and pin 4 is the -15 rail.

I made some measurments in play mode. Got any tape you can spill?

IC10 pin2 0.37v
IC10 pin6 2.65v
IC8 pin2 0.38v
IC8 pin6 0.38v
IC9 pin2 1.01v
IC9 pin3 1.12v
IC9 pin6 2.04v
IC7 pin2 -6.7v
IC12 pin2 0.36v
IC12 pin6 0.49v
IC25 pin3 0.36v
IC25 pin1 0.36v
IC26 pin6 -3.89v
IC27 pin6 4.36v

Here is a question. What happens when you put tape in the deck and press stop. Does the tape move or just go into tension? If you touch the MVC (joystick) will the tape move left and right as commanded?

Regards, Ethan
 
evm1024 said:
Here is a question. What happens when you put tape in the deck and press stop. Does the tape move or just go into tension? If you touch the MVC (joystick) will the tape move left and right as commanded?

Regards, Ethan
Click to expand...

I haven't loaded tape since both reels stopped functioning but with a card in the tape sensor I can tell you that the MVC does just what it's supposed to and stop takes the machine out of play/rec/FF/RW ok. I also did already check IC pins 7 and 4 all over the torque board and got near as makes no difference to +/-15v; FWIW the PSU voltages have always checked out within tolerance when I measure them.

Thanks hugely for your reference measurements!! Dumb question--is loading tape a must here? All I've got to work with right now is a blank roll of 499 that I'd rather not let the capstan drag off the reel and onto the floor if I can get reliable measurements just sticking a business card in the sensor-
 
You should save that 499.

The capstan and reel motors are all servo controlled. Which means that their drive voltages are dependent on speed and load. Without tape the voltages will need to be different (and would be different than mine anyway due to cal differences).

But, this is a signal chain of voltages so getting their values may tell us something.

With tape in the machine you can monitor the voltage on TP2 or any of the other points (IC25 pin1 etc) and watch the voltage change as you apply drag to the reel flange. This causes the servo loop to drive the motor more to keep a constant torque.

It is important to make sure that IC25 pin 3 (signal into the fet switch) and pin 1 (output to drive buffers) are the same. This will tell us that the fet is working OK.

Regards, Ethan
 
OK good, I was hoping putting some drag on the reels would give enough of an approximation. I should be able to do these tests this afternoon and will report back...thanks again!
 
evm1024 said:
Always a good idea to check the supply rails. You can measure it on the 741 opamps on the analog torque board. Pin 7 is the +15 rail and pin 4 is the -15 rail.

I made some measurments in play mode. Got any tape you can spill?

IC10 pin2 0.37v
IC10 pin6 2.65v
IC8 pin2 0.38v
IC8 pin6 0.38v
IC9 pin2 1.01v
IC9 pin3 1.12v
IC9 pin6 2.04v
IC7 pin2 -6.7v
IC12 pin2 0.36v
IC12 pin6 0.49v
IC25 pin3 0.36v
IC25 pin1 0.36v
IC26 pin6 -3.89v
IC27 pin6 4.36v

Here is a question. What happens when you put tape in the deck and press stop. Does the tape move or just go into tension? If you touch the MVC (joystick) will the tape move left and right as commanded?

Regards, Ethan
Click to expand...


OK, I did load up some tape and just did my measurements quick before the right reel crapped out and too much tape spilled off...and here's what I got (now remember that the right reel only runs for a few seconds in play before coming to a halt again so some voltages in play were "moving targets" so where applicable I'm noting the maximum reading before the reel stopped):

First, IC 25 pins 1 and 3 both read 0, nada, whether in play/stop/dragged by hand--so that's something!

IC10 p2 - 0
IC10 p6 - 0 when reel stopped; ~5v at peak play speed
IC8 p2 - 0
IC8 p6 - 0
IC9 p2 - 2.9v at peak play speed
IC9 p3 - same as pin2
IC9 p6 - 5.4v peak play speed
IC7 p2 - -14.3v in stop; 10.4v peak play speed
IC12 p2 - -.01v
IC12 p6 - same as p2
IC25 p3 - 0
IC25 p1 - 0
IC26 p6 - +0.26v
IC27 p6 - -0.25


So it does appear that IC25 is a culprit and is affecting things upstream, no?
 
Nope

It looks like you are getting a tach signal through IC7 which compares the reel speed to the capstan speed. But that that signal is not making it to the play inverter IC12.

What is the position of pot R41? I expect that if it has not failed that it is all the way to one side. Move it to the mid point and see what happens. Also, measure IC 12 pin 2 just to be sure that some signal is getting through R41.

Measure the voltage at the IC7 side of R41.

What could be bad.... R41 could be open, C2 could be a short to ground, CR4 could be a short to ground. Broken traces in the path IC7 pin 2 to IC12 pin2. IC12 might be bad....

Regards, Ethan

I think that you are getting closer.
 
evm1024 said:
It looks like you are getting a tach signal through IC7 which compares the reel speed to the capstan speed. But that that signal is not making it to the play inverter IC12.

What is the position of pot R41? I expect that if it has not failed that it is all the way to one side. Move it to the mid point and see what happens. Also, measure IC 12 pin 2 just to be sure that some signal is getting through R41.

Measure the voltage at the IC7 side of R41.

What could be bad.... R41 could be open, C2 could be a short to ground, CR4 could be a short to ground. Broken traces in the path IC7 pin 2 to IC12 pin2. IC12 might be bad....

Regards, Ethan

I think that you are getting closer.
Click to expand...

I think I am too, thanks to your kind help!


I'll check these out, hoever one thing to note is that I suspected R41 a while back and actually soldered in a brand new one, so I wrote that one off as a culprit...I thought I set it to midpoint but I'll double check...I have also subbed in a brand new chip in IC12 and a new C2 and no change...

I'll double check CR4 and trace between IC7p2 and 12p2...I'll especially take a gander at the traces...I'd swear I've traced continuity between there before, but I want to double check! Sounds like we're closing in on it...
 
Last edited:
Woohoo! I got it back! I wound up changing out ICs 6 and 12 AND had to turn and turn and turn....and turn and turn and turn and turn...and tuuurn and turn and TURN that damn R41 for ages until slowly but surely the right reel started taking up tape again!

Busted out the Tentelometer, tweaked the dancer arm and I can say that for the first time since I laid hands on this machine, the tape tension is correct! :)

I'm going to check and re-set up the transport from scratch to make sure it's happy and then hopefully be able to move onto the audio without more hassle from the transport...

The audio drawers are gonna be another adventure entirely...call it a hunch :D

*keeps the Weller warm*
 
briank said:
Woohoo! I got it back! I wound up changing out ICs 6 and 12 AND had to turn and turn and turn....and turn and turn and turn and turn...and tuuurn and turn and TURN that damn R41 for ages until slowly but surely the right reel started taking up tape again!

Busted out the Tentelometer, tweaked the dancer arm and I can say that for the first time since I laid hands on this machine, the tape tension is correct! :)

I'm going to check and re-set up the transport from scratch to make sure it's happy and then move onto the audio...

The audio drawers are gonna be another adventure entirely...call it a hunch :D

*keeps the Weller warm*
Click to expand...

Outstanding! And congratulations. Servo loops are a bit harder than most. The drawers will be easy.

Regards, Ethan
 
briank said:
Busted out the Tentelometer, tweaked the dancer arm and I can say that for the first time since I laid hands on this machine, the tape tension is correct! :)
Click to expand...

From this point forward you shall be known as - the "MCI Whisperer"
:laughings:

sorry, couldn't help it. Good job, man.
 
Well I'm going to have to do some whispering at the audio drawers (as swearing didn't seem to help :D )...only one and a half channels seem to be getting (or should I say passing) signal or capable of going into Rec Ready--both in the same drawer...sooo I've got some more tracing, cleaning and re-soldering to do :spank:

Still I feel I'm past the hardest part and this machine will be in service sooner than later!

Also I would have to agree completely with those who say that these machines have personalities...this one especially has its own ideas about what to do when tape starts rolling and it's clearly a machine of the 80's as the dancer arm has been known to do some breakdancing :p ...I asked my studiomate (the rightful owner of the machine) if it has a name, since it has such a fussy temperament. He said it doesn't, but agrees it needs one. One thing we agreed on is its gender...I'll give you one guess :D
 
You must log in or register to reply here.
Back
Top