[QuadList] TR-600 Control Track/Capstan Servo Issues

Tue Nov 12 11:11:56 CST 2013

Thanks, Chris!  For this information and the phone calls yesterday.  I had
to have work done on the car yesterday, so I didn't get across town to the
other studio, but I am heading over there in a few minutes.  I'll give a
full report to the list when I get back.

Fred Kovach

Broadcast Technician

417-848-8381

  _____  

From: QuadList [mailto:quadlist-bounces at quadvideotapegroup.com] On Behalf Of
chill315 at aol.com
Sent: Monday, November 11, 2013 5:59 AM
To: Quad List
Subject: Re: [QuadList] TR-600 Control Track/Capstan Servo Issues

Interesting problem. 

 Did you demagnetize the control track head after checking continuity?  

Is there edge damage on the problem tape?

     Fugi tape uses a stiffer base layer and is renown for being easy to
damage.  If there is a little scalloping on the lower edge, that would be an
issue.  

What does the control track playback waveform and level look like?  I see
that you tell us the level changes a couple of minutes into the program.
But does the control track show the saturation bump?

Comments.  Using capstan speed override shows that all other parts of the
machine are working.  The unlock every few seconds is normal since there is
no control of the capstan.  

This may be a tape for an AVR-1. The machine that can play anything.

Chris Hill

On Nov 10, 2013, at 9:38 PM, "Fred Kovach" <fkovach at sbcglobal.net> wrote:

Note: I sent this originally on October 31, and it apparently never posted
(I wondered why I never received any replies!!!)  :-)  

I have since added a couple of notes of what Ibve done.  Any advice that you
can give me would be greatly appreciated.

I am working on a RCA TR-600A thatbs having a tracking issue.  This has been
an ongoing problem for about three months; and my usual source of
information is at a loss.  Hebs been very helpful and gone out of the way to
help me; but I think it is time for me to check with you guys on this.

It is not locking up to control track on what was our most reliable playback
tape (FUJI tape stock).  After some amount of troubleshooting on the C18 CT
Amp card, I found two bad chips: U1 and U7 that was basically switching
between the pb and rec CTL heads.  So the machine was in PB mode, but half
the card thought it was in record!  I also replaced some capacitors on that
card, After that, it would still not lock up on the FUJI tape, but would
lock up to a VTC tape stock that had a higher level CT track on it.
Actually, it wouldnbt lock at the beginning of the tape where the CT was
lower level, but apparently whoever recorded in, turned up the record
current about 2 or 3 minutes in!

I have done the following:

1.	Checked continuity from the CTL head to the C18 card. 
2.	Checked grounds/shields on the same path. 
3.	Checked power supply voltages at the power supply and the card. 
4.	Replaced a flaky R307 on the power supply, which was throwing the
+12 VDC supply all over the place whenever I even thought of touching it! 
5.	Cleaned the power supply interface molex connectors with contact
cleaner. 
6.	Checked grounds on the back plane. 
7.	Checked wirewrap connections on the back plane.  Especially those
that I re-did in Summer 2012 when I took out the Auto Editor (AE600) on the
advice of my friend. 
8.	Thoroughly cleaned the path and checked out the problem with two
other spare headwheel assbys we have on hand.  However, the HW assby that I
had in there has the best performance.  My friend found that it had less
than 1 micron wear; so I put it back in.  Also adjusted tip penetration and
scalloping. 
9.	Checked the inputs from our sync generator.  
10.	Varying the capstan speed from the control panel, will bring it
pretty close to locking up, but of course, you have an boccasionalb skip
every two or three seconds. 
11.	Had my friend check a boatload of cards in his machine, all of which
worked, except the aforementioned C18 card, which in spite of my best
efforts apparently still had issues (see below). 
12.	Swapped C18 cards with another known to be good after my friend
found that my C18 card didnbt work in his machine.  After the new card, the
VTC tape would lock up a little earlier in the program.  So that was
progress.  J  But still no lock on Old Reliable Fuji tape.  Also, Ibve had
to abandon the VTC tape, as it was clogging up the heads a lot; even after
baking it.  Donbt want any more trouble than I have already!  ;) 
13.	Varied the three pots on the C19 card (capstan balance, symmetry and
level, I think) and one on the C20 card.  All on the advice of my friend, to
see if they helped.  We got perhaps marginal improvement. 
14.	Therebs probably a few other things that Ibve forgotten.  If
necessary, Ibll post them as I remember them.  But I did write my work down,
so this ought to be most of them. 
15.	I went through the capstan servo alignment section of the manual
(ecept for the record functions, since this machinebs record doesnbt work),
and found it needed some minor adjustments.  However, nothing major.  I did
find that the Color Framer card was missing and in itbs place was the Guide
PA card!!  However, Ibm told that the Color Framer is only used for editing
and is not necessary for playback.  The Guide PA card works just fine in its
proper place.  But it didnbt solve the problem.  And I should note that
since apparently these two cards have been out of place for some time, that
the machine would have been working fine with them out of place.  If this
makes senseb&. 

I am thinking of doing the following the next time Ibm there, which might be
tomorrow (Monday):

1.	Digging into the backplane a little deeper and confirming all the
mods I did when I removed the AE600.  Ibve already done this thoroughly
once, but my friend thinks the problem might be there; so Ibll do it again. 
2.	Checking the levels coming off the CT heads of the three different
headwheel assbys to see if I can find any kind of pattern for this. 
3.	Checking the circuitry surrounding the CT Phase adjustment because
when it does playback the VTC tape properly, I have to turn it fully
clockwise for it to lock up.  Is there a way to get it so that this control
works closer to the center of the pot? 

I appreciate any help you can give me on this.  I may be able to take some
pics or video of waveforms if it would help.

Thanks so much!

Fred

Fred Kovach

Broadcast Technician

417-848-8381

______________________________________________
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