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+  MCI Console and Tape Machine Forum
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 on: March 25, 2017, 10:21:02 AM 
Started by Phillip V Bova - Last post by LarryL
Well, we have new owners now and the board will be around awhile longer.


And the new owner is probably the most knowledgeable MCI tech on the forum, with over 40 years hands on real world experience!

 on: March 24, 2017, 10:08:54 AM 
Started by Phillip V Bova - Last post by brianroth
Well, we have new owners now and the board will be around awhile longer.


 on: March 22, 2017, 10:05:17 PM 
Started by Phillip V Bova - Last post by MindRocket
Agreed Philip .

 on: March 18, 2017, 07:44:41 AM 
Started by Robomatic - Last post by Harrison
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.

 on: March 07, 2017, 03:37:12 PM 
Started by Robomatic - Last post by brianroth
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.


 on: March 07, 2017, 12:09:31 PM 
Started by ghalik - Last post by ghalik
heres the whiz Tristan talkng about the studio....looks great


 on: March 07, 2017, 11:40:49 AM 
Started by Robomatic - Last post by Robomatic
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?

 on: March 04, 2017, 05:44:41 PM 
Started by Robomatic - Last post by Harrison
You did not answer the question.
The pot is a distortion trim for the VCA. ie a trim for a minimum.

The old best way is with SMPTE IMD, although some will prefer THD.
And then there's the discussion as to where the fader is when you set this value. MCI used the Crown/Amcron IMD analyser with the fader at the top and measure at the following 2003/5534.

BUT, since we rarely use the fader at the top, would it not be better to optimise the trim at fader zero as opposed to VCA zero. ie you get different results depending on which position you choose.

In the absence of any test gear, you could do this adding 2 out of phase signals together. 2 identical line in, but one has fader flip. Set both to the same gain and to the same left or right. phase change one.
Adjust one of them to really null out signal, then adjust distortion trim to improve that nulling

The point being that the one with the rotary pot will be slightly cleaner than the one with VCA. (If you've got black 202s, this is really obvious), and what you can't null out is the remaining VCA artefact.

But of choice, some form of distortion measurement, please.

 on: March 04, 2017, 12:31:06 PM 
Started by adamb - Last post by adamb
Following up on this with the solution I found.

There was an incorrect capacitor value in C3 on the record card.   Spec calls for a 10uf, someone put in a 1uf.   This caused a dramatic low end drop starting at 200Hz, down -4db at 50Hz.

I replaced the cap with a new, to spec cap and everything on the low end looks much better :-)

 on: March 03, 2017, 08:53:15 PM 
Started by Robomatic - Last post by Robomatic
Wanted to check them. Is there an easy way to do this?

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