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

[chill315 at aol.com]

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!!!)  J 
>  
> I have since added a couple of notes of what I’ve done.  Any advice that you can give me would be greatly appreciated.
>  
>  
> I am working on a RCA TR-600A that’s having a tracking issue.  This has been an ongoing problem for about three months; and my usual source of information is at a loss.  He’s 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 wouldn’t 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:
> Checked continuity from the CTL head to the C18 card.
> Checked grounds/shields on the same path.
> Checked power supply voltages at the power supply and the card.
> 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!
> Cleaned the power supply interface molex connectors with contact cleaner.
> Checked grounds on the back plane.
> 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.
> Thoroughly cleaned the path and checked out the problem with two other spare headwheel ass’ys we have on hand.  However, the HW ass’y 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.
> Checked the inputs from our sync generator. 
> Varying the capstan speed from the control panel, will bring it pretty close to locking up, but of course, you have an “occasional” skip every two or three seconds.
> 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).
> Swapped C18 cards with another known to be good after my friend found that my C18 card didn’t 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, I’ve had to abandon the VTC tape, as it was clogging up the heads a lot; even after baking it.  Don’t want any more trouble than I have already!  ;)
> 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.
> There’s probably a few other things that I’ve forgotten.  If necessary, I’ll post them as I remember them.  But I did write my work down, so this ought to be most of them.
> I went through the capstan servo alignment section of the manual (ecept for the record functions, since this machine’s record doesn’t work), and found it needed some minor adjustments.  However, nothing major.  I did find that the Color Framer card was missing and in it’s place was the Guide PA card!!  However, I’m 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 didn’t 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 sense….
>  
> I am thinking of doing the following the next time I’m there, which might be tomorrow (Monday):
> Digging into the backplane a little deeper and confirming all the mods I did when I removed the AE600.  I’ve already done this thoroughly once, but my friend thinks the problem might be there; so I’ll do it again.
> Checking the levels coming off the CT heads of the three different headwheel ass’ys to see if I can find any kind of pattern for this.
> 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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