Conference turris::video

I have an about 10-year-old Panasonic S-VHS  VCR (47xx) that produces an output
signal with which both TV sets I own have vertical sync problems.

Basically, the output loses vertical sync often on one set, and just jitters
vertically on the other.

This problem occurs on both tapes being played and on fed-through output of the
VCR's tuner (no tape involved).

When I play a tape and put the VCR on "pause", the still picture slowly rises and
falls (once or twice per second) on one of the sets.

This VCR is probably not worth repairing.  Is this symptom more likely a mechanical or
an electrical problem?  Is there any likely adjustment that I could make that could be
causing this?

Thanks,
Bob

    re: .-1
    
    From the sound of the problem, this may only be an adjustment.  Does
    the tracking control effect the picture at all?  When in Pause, does
    the entire picture rise and fall or does it shrink up then expand back
    to normal?
    
    Dan

> This problem occurs on output of the VCR's tuner (no tape involved).

> Is this symptom more likely a mechanical or an electrical problem?

	Since it happens without a tape it is likely to be an
	electronics problem.  There may be an adjustment in the 
	VCR for sync level.  If the variable resistors are not
	labeled, try each one.  Be sure to start with each one 
	by noting its current position so you can set it back if
	it doesn't help!

    re: .-1 etc
    
    After reading .-1,  I re-read the initial note.  I missed the passthru
    reference.  That in mind...
    
    Check for cold solder joints in the RF converter. Specifically check
    the ground connections.  The metal case should be grounded at each
    side.  If these joints look grainy, resolder them.
    
    DON'T adjust any pots unless you can be sure that you can return them
    to the EXACT starting position.  In passthru mode, there is little to
    no intervention of the signal.  There are usually only a few components
    in the loop.  (switching transistors).
    
    If the RF converter is out of whack, then adjustments should be made
    with injected signals of known quality.  Its unlikley that a hit or
    miss adjustment will last or correct the true problem.
    
    Another diagnostic would be to connect the TV using the VIDEO out jack. 
    If the problem persists, then the RF converter is OK.  Given that the
    problem occurs both with tape playback AND tuner, I'd suspect the
    converter.
    
    
    Dan

re Note 406.92 by CPEEDY::FLEURY:

>     From the sound of the problem, this may only be an adjustment.  Does
>     the tracking control effect the picture at all?  When in Pause, does
>     the entire picture rise and fall or does it shrink up then expand back
>     to normal?
  
        Adjusting the tracking does nothing but cause the usual
        symptoms of mis-tracking in addition to the vertical sync
        problem.  When in Pause, the entire picture rises and falls
        -- no shrinkage/expansion.

re Note 406.94 by CPEEDY::FLEURY:

>     Check for cold solder joints in the RF converter. 

        The problem is actually worse (slightly) via the video
        outputs.

        Actually, it wasn't until last night that I even tried
        looking at the RF output, since I normally use the A/V route.

>     Another diagnostic would be to connect the TV using the VIDEO out jack. 
>     If the problem persists, then the RF converter is OK.  Given that the
>     problem occurs both with tape playback AND tuner, I'd suspect the
>     converter.
  
        Thanks so far -- any other suggestions?

        Bob

> Thanks so far -- any other suggestions?

	There may be an adjustment in the VCR for sync level.  If 
	the variable resistors are not labeled, try each one.  Be 
	sure to start with each one by noting its current position 
	so you can set it back if it doesn't help!

    RE: .-2
    
    Since the picture rises and falls when in Pause, I'm now leaning more
    toward a power supply problem.  Can you enter the make and model. This
    may be a bad filter cap in either the power supply directly or within
    the tuner area.
    
    RE: .-1
    
    Please do not alter ANY pot without completely understanding what they
    are for.  There are many adjustments which can be made which will not
    necessarily be visible on a screen, but which will alter the
    performance of the machine in general.  Unless you have the proper
    equipment to examine waveforms etc, don't arbitrarily adjust them.
    
    Dan
    

re Note 406.97 by CPEEDY::FLEURY:

> Can you enter the make and model. 

        Panasonic PV-S4764

        Several years ago that unit did have other problems which
        were fixed by a visit to Panasonic service (almost $100 just
        to look at it!!) -- they said they replaced a bunch of caps.

        Thanks,
        Bob

    RE: .98
    
    I'm going to guess that the previous repair included caps in the power
    supply.  It sounds like this may be the most likely problem again.  The
    PV-S47xx series uses switch mode power supplies which can fail in a
    number of ways.  A leaky diode in the "secondary" can leave enough
    variation on the line to cause what you are seeing.
    
    The bottom line is that this does not appear to be a "home repair". 
    I'd suggest you bring it to a shop which has the proper equipment to
    troubleshoot this problem.  Please also bring in as much detail about
    the failure/problem as you have provided here.
    
    Dan