The MCI Saga begins

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Muckelroy

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Ok, maybe I should ditch the theatrical aspect and just tell the story.

We're trying to resurrect our MCI JH-110, and bring it up to spec for 1/2" 2 track 30 ips mixdown :D

The thing hasn't been powered on in about 10 years. There was only one blown IC chip on the analog torque card. So to begin with, I bought 8 of those kinds of chips (made by texas instruments. piece of cake.) We blew all the dust out of the machine, removed the charred IC, sprayed some contact cleaner on the socket, and replaced the chip. Threaded a junk reel of tape, crossed our fingers, and hit the power switch. It sporatically fast-forwarded the tape, both motors running in opposite directions, which seemingly made the tape run slower, and slower, till it made a grinding noise, and we killed the power. (no, this was not sticky shed, so please don't suggest that) The transport controls did nothing to alter this behavior.

Then we smelled the all too familiar smell -- ozone. That very same IC chip had fried again. (for those who are curious, it's IC 21 on the component diagram.) We looked at the schematic, and LO and BEHOLD, a capacitor near the component looked like the top of the cap was kind of bulged out. This is apparently a sign that the cap is dried out and needs to be replaced. Well, now it all makes sense. If the capacitor is dried, it's sending WAY too much current to the chip. This board is primarily a logic circuit. It does NOT require very much power to determine what's going on with the transport. So next step is to replace the cap as soon as one can be acquired. (It's a 100 mF 35 Volt cap, down and to the right of IC 21.) And replace IC 21 again. Rinse, wash, repeat, cross fingers.

Wish us luck!

-callie-
 
more to the storie....

Sounds mote to me like you have a faulty power rail that is feeding both the IC and the cap. The cap may be dry as well. What is the part number of the IC?

The other thing that may fry an IC is if some down stream device is drawing too much power from it.

So measure each voltage rail in the power supply one at a time and see if they are all in spec. (Set probes, power on, read measurement and thurn off. Do again on the next rail) This will hopefully keep you from blowing up the next IC.

If it is dead then just turn it on and verify the supply rails.

Ethan
 
I would agree with you, except that only one IC is affected. I think that if it were a power rail problem, several, or all of the IC's would be affected.

This cap is directly linked to this IC. So, as soon as we replace the cap, that should (hopefully) stop things from blowing up, anyway. Thanks for the input, though. It's definately a possibility, and I'm not ruling out anything.

-callie-
 
I had prety much the exact same thing happen to my itam 806, which is based on a revoz a77.

The problem there was a bulging cap. Replaced it and all is well. Sept whin i was looking for the problem i shorted the PS and now it is supplying the channel cards with 5v instead of 21. But hey... i fixed the transport :(
 
It's Alive!!!!!!

REALLY excited right now!


I finally got around to continuing this project. I took out the analogue torque card, and replaced the cap in question. This was my first attempt at desoldering and soldering on a PCB card. I finally got the cap replaced, and replaced IC 21 again.

I put the torque card back in, fired her up, and there it was, meters glowing, tape standing still as ever. :-)

It seems to be running pretty close to the correct speeds, it just has several tension issues. Rewind doesn't have enough pull in it, and every time it stops, it lets tape slack out, things to that nature.

Sometime or another, we'll go through and check all the caps, to see if they're dry or not, do more cleaning, and tension adjustments, and bring it back into service. :D

And maybe show my peers why I keep ranting and raving about the sonic superiority of analog

-callie-
 
Cool

Thats pretty exciting and I am happy that you are making progress. And a bit envious as that I would like to have a MCI/SONY 2 track.

Keep us posted!

As a side note: Do you have a solder sucker? It is a plunger kind of thing that you can pick up at radioshack and makes desoldering easier. Also, clipping the leads can at times make it less work. Also, also, I like to take a photo of the boards before I start swapping out things as that it allows me to "remember" just what the right way was. (forgive if this is not new to you)

Regards, Ethan
 
Muckelroy said:
Sometime or another, we'll go through and check all the caps,
Click to expand...

Sooner would be better than later. It's false economy to "inspect" and "check" electrolytic caps that are this old. Just replace them all and you'll have a far more enjoyable time recording with the machine instead of constantly having to troubleshoot problems. Replacing caps is CHEAP insurance.

Cheers,
--
Don
 
idylldon said:
Sooner would be better than later. It's false economy to "inspect" and "check" electrolytic caps that are this old. Just replace them all and you'll have a far more enjoyable time recording with the machine instead of constantly having to troubleshoot problems. Replacing caps is CHEAP insurance.

Cheers,
--
Don
Click to expand...

Come to think of it, that would be a very wise thing to do. Already, one cap has failed, so I suppose it would be wise to recap the whole thing.

And YES, we have 2 solder suckers. I tried to use it when I was desoldering the cap, but it didn't do too much for me. I must have been using it wrong. I had much better luck by holding the iron to the solder, and yanking the cap off quickly while it was still melted.

Thanks for the tips.

-callie-
 
Muckelroy said:
Come to think of it, that would be a very wise thing to do. Already, one cap has failed, so I suppose it would be wise to recap the whole thing.
Click to expand...

Think about it this way. Electrolytic caps, especially from this era, were designed to have about a 10-year lifespan, and it speaks very highly for the mfgs. that many of them made it much, much longer. Over time, though, they fail or start to perform at less than stellar levels, and this process is hastened by the higher temperatures usually found in gear like this. It's always a good idea to recap old electronics gear. That way, you'll really get to hear what it truly sounds like, not some distorted, muddy, and smeary sounding garbage that's the result of marginal caps.

And YES, we have 2 solder suckers. I tried to use it when I was desoldering the cap, but it didn't do too much for me. I must have been using it wrong. I had much better luck by holding the iron to the solder, and yanking the cap off quickly while it was still melted.
Click to expand...

I completely recapped my 28-channel Neotek console a couple years ago, and I just finished up a complete recap of an MCI JH24 2", 24-track machine, and let me tell you there were thousands of caps! I don't know if your MCI has the same kind of PCB design, but the JH24 used dual-sided PCBs with plated-through holes. Needless to say, a simple solder sucker doesn't work too well in this case. I use a Plato desoldering station, and it makes the job much, much easier.

Another thing to keep in mind is that you don't want to overheat the traces as you'll start to lift them from the board. I'm not trying to scare you off, but just want to give you a heads-up. I think if you heat up the solder joints and remove one leg of a capacitor at a time you'll be OK. Once you get the cap off the board, then you'll have much better luck cleaning out the holes with a regular solder sucker or some braid.

Cheers and good luck.

Don
 
We continued working on the MCI today. Like I said, it's stable when it's powered on, but the transport leaks out tape when you hit stop, the tension's off, and I think the idle doesn't work.

The first thing I noticed was that the brake solenoid on the takeup side wasn't letting go of the brake band all the way when the brake was disengaged. Because of this, the brake band was still sort of gripping the motor shaft, and causing excess friction, and a lack of torque to take up the slack when stopped.

We didn't find a problem with the solenoid itself, or with the solenoid driver card components. However, the solenoid, when disengaged, could easily pop back into itself by pushing it w/ your finger. So we decided to loosen up the spring attached to the brake lever and the solenoid. We didn't loosen the bolts on the spring, as they were painted over, and glued into place, so I just gave the spring a slight tug to loosen it up a tad, just enough to allow the brake to disengage all the way when it was supposed to.

That being fixed, we hit the service manual for the offset null, idle, and tension adjustments. While trying to adjust the offset null, the multimeter kept reading 12 Volts, when it shoudl have been reading close to 0 volts. And, the tweakers were not doing a damn thing.

So, I tried to adjust the idle. (I DID follow all the instructions in the manual meticulously,) and no matter how much I tweaked it, no idle would happen on any of the motors.

I then saw on the schematic that the potentiometers and the voltage went to an AND gate, which went to the motors. There's lots of other voltages involved here, so I'm thinking that it HAS to be a problem with the power supply, or something related. Some power rail is either getting NO power, or not the right amount of power, which is messing up the logic gates and causing all the tweakers to not work on the analog torque card.

To be continued. At least the thing doesn't smoke anymore :D

-callie-
 
OK, back to the soldering bench at long last!

I recapped the analog torque card, which had 8 remaining caps to be done.

2 questions:

1: I replaced a ceramic plate cap that was 0.01 micro-farad 100V max, with a 0.01 micro-farad 500V max cap. Is THAT ok?

2: A couple of the replacement caps were non-polar, contrary to the originals. Is it OK to put non-polar caps in place where polar caps used to be?


Only because our Radio Shack has a terrible selection. But if it works, it works.

I'd appreciate some seasoned advice before I fire 'er up again tomorrow!! Thanks!!

-callie-
 
Yep. It's OK to replace with a higher VOLTAGE rating.
 
So, is it OK to replace polar caps w/ nonpolar caps of the same spec?

thanks!!
 
Welp, did some research.

Polar caps block DC voltage. So, it's VERY BAD to put non-polar caps in the place of polar caps, as DC will go to places it shouldn't go, and things will get rather smoky.

And forget radio shack. Digikey.com is better and cheaper, turns out. What was I thinking??
 
I read through pretty much the entire service manual. WHAT AN INCREDIBLE piece of machinery this thing is! I'm reading through, just astounded at how all of these features work together, and make it perform..........

Only It's NOT right now. sigh...........

SO I went through the schematic diagrams and counted all of the caps in the machine (only in the cards that were installed in THIS model, of course).

403 caps.

Not all of them are electrolytic, of course, so that number will probably be reduced by half when I decide what cards have priority over what to get it working again.

I think phase I of the recapping process will be to recap the power supply, and the analog torque board. Then I'll check the power rails when I'm done with the power supply.

Lord willing, if the power supply works right, I'll check to see if the torque work yet. If I'm still getting a 12 volt reading on the offset null test points, something is DEFINATELY wrong. I may need to replace some IC's on the torque card. THe manual pointed out about 7 or 8 IC's that are involved in the play/rec mode which may need replacing if the torque doesn't function in that mode.

So as soon as I can jot down what caps I need to buy, I'll order them and get started with the power supp. and torque board.
 
Muckelroy said:
Ok, maybe I should ditch the theatrical aspect and just tell the story.

We're trying to resurrect our MCI JH-110, and bring it up to spec for 1/2" 2 track 30 ips mixdown :D

The thing hasn't been powered on in about 10 years. There was only one blown IC chip on the analog torque card. So to begin with, I bought 8 of those kinds of chips (made by texas instruments. piece of cake.) We blew all the dust out of the machine, removed the charred IC, sprayed some contact cleaner on the socket, and replaced the chip. Threaded a junk reel of tape, crossed our fingers, and hit the power switch. It sporatically fast-forwarded the tape, both motors running in opposite directions, which seemingly made the tape run slower, and slower, till it made a grinding noise, and we killed the power. (no, this was not sticky shed, so please don't suggest that) The transport controls did nothing to alter this behavior.

Then we smelled the all too familiar smell -- ozone. That very same IC chip had fried again. (for those who are curious, it's IC 21 on the component diagram.) We looked at the schematic, and LO and BEHOLD, a capacitor near the component looked like the top of the cap was kind of bulged out. This is apparently a sign that the cap is dried out and needs to be replaced. Well, now it all makes sense. If the capacitor is dried, it's sending WAY too much current to the chip. This board is primarily a logic circuit. It does NOT require very much power to determine what's going on with the transport. So next step is to replace the cap as soon as one can be acquired. (It's a 100 mF 35 Volt cap, down and to the right of IC 21.) And replace IC 21 again. Rinse, wash, repeat, cross fingers.

Wish us luck!

-callie-
Click to expand...

MCIs in general have many little perculier design bugs that prevent them from being very reliable machines. All are fixable and you just have to know about them. Re-capping is a great idea, but you should try to get the machine running before you re-cap. Some things to know:

Transport issues can be caused by the high current motor drive transistors found on the transport power supply. When they blow, the reels go nuts.

Look at your boards and see if there are "red" sockets holding the ICs in. IF you have them, get rid of every last one. Carefully clean ALL molex connections on the entire machine with De-oxit. 99% of all problems that ever happen with these machines are caused by bad connections in any one of the 1000 connections! THIS is where you should concentrate on. If you can fix these things, the machine will be very reliable.

I will remember about 100 more things later

Good Luck.
 
AH, I've heard of the infamous red sockets.

But there are none in this machine, thank GOD!

I will take your advice on the motor drive transistors.

We'll recap only a couple of boards at a time, while doing general cleaning-up and IC testing. Wish me luck!
 
Muckelroy said:
Welp, did some research.
Polar caps block DC voltage. So, it's VERY BAD to put non-polar caps in the place of polar caps, as DC will go to places it shouldn't go, and things will get rather smoky.
Click to expand...
Any chance to know the source or the finding?
thanks

/respects
 
Actually, I went back to Radio Shack.

The guy who had helped me before had a big ol' binder of employee training materials, complete with electronics marking codes, and simple facts.

I asked. He looked it up in the capacitor chapter of his book, he showed me.

Wasn't expecting that kind of help from Radio Shack. I was impressed.
 
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