On Sunday, April 15, 2012 3:05:26 AM UTC-4, N_Cook wrote:
wrote in message
news:1387820.1545.1334470225266.JavaMail.geo-discussion-forums@ynei5...
On Saturday, April 14, 2012 3:37:14 PM UTC-4, wrote:
On Apr 14, 10:04 am, Mike S wrote:
Hi,
I'm a total beginner, but I have a pretty simple VCR issue that doesn't
appear to be covered in Sam Goldwasser's VCR FAQ
(http://www.repairfaq.org/sam/vcrfaq.htm) or David T. Ronan's Practical VCR
Repair, based on the skimming I've done.

When I'm stopping or ejecting a tape, my back tension regulator takes
too long to move out of the way, and the left shuttle assembly gets blocked
on it - and pins it in place - on its way back to the front of the VCR.
Basically, the two parts end up jamming each other, so neither can move, and
it screws up the timing of the two shuttles as well as the gears underneath
slip teeth.

What exactly is the mechanism that is supposed to make the back tension
arm retract away from the full erase head and toward the tape door? Is it
supposed to sit passively while the left shuttle assembly pushes it back
toward the front, or is the VCR supposed to apply power to explicitly move
it out of the way? If the VCR is meant to explicitly apply power, what
controls the timing of this?

I half-expected this issue to be a common cause of jams and thoroughly
covered by VCR repair resources, since the back tension arm literally
crosses the path of the left shuttle assembly, but I haven't found anything
about it yet. I can't imagine I'm the only person in the world who has ever
had this happen to them.

My VCR has other issues that bring about this behavior initially, but
this is the most pressing problem due to the potentially damaging nature of
a jam like this and the difficulty of removing tape afterwards. (Usually the
VCR will work fine...but using my VHS-C adapter revealed a problem with the
source spindle. After an initial error occurs, the machine stops. After
cycling power again to eject, it jams the shuttle and back tension
regulator...and once that happens, it breaks down on playback and jams on
every eject attempt until it's "fixed." I "fixed" it once before by magic
and got it working again with regular tapes, but trying the VHS-C adapter
again caused the jam once more, and I'm trying to understand what's going on
this time.)

Thank you for your time!

Sony broadcast tape transports have issues with lubricants drying
out / thickening up which causes problems similar to yours. The cure
is to disassemble the component, clean out the old junk and re-
lubricate. Since their lubricants were bad to begin with I don't use
Sony lubes. Nye Oil II is a vastly better light machine oil. A 2 oz.
bottle is about $9. Sony SGL grease can be subbed with Nye Rheolube
363F but that stuff is expensive. Do NOT use Lubriplate as it's even
worse than SGL as it separates. And whatever you do do NOT use WD-40
for ANYTHING in electronics.

G²

Thank you! I have the service manual, so I'll look into which parts need
lubrication, and I'll use Nye Oil II as you suggest.

Nevertheless, the back tension arm does not appear to be particularly
resistant to movement: I can move it very easily with my finger when it's
not jammed, and the only resistance I feel appears to come from the
spring...it just happens not to retract on its own when it counts. Do you
know whether it's meant to retract actively (powered by electricity) or
passively (pushed back to the front by the left shuttle assembly)?


++++

Could a gear train/ rack or the mode switch have jumped a tooth, look for
alignment marks or holes in gear wheels etc, maybe in the manual. If 2 or
more teeth then usually a fully corrupt system but just one tooth and can
get intermittant good/ bad operation

Thanks for your response! It's possible it had already slipped a tooth, making the left shuttle early. That said, at this point I know it has slipped multiple teeth in the other direction: The jam caused tooth slips which significantly delayed the left shuttle. Thankfully the gears are still intact, but they'll definitely be realigned. I'm not confident the problem is an early left shuttle though for two reasons:
1.) You'd think the jam itself would fix that, since it slipped teeth in the other direction.
2.) I'm still not sure whether the back tension arm has a timed retraction, or whether the left shuttle assembly is just meant to push it toward the front whenever it moves. If the back tension arm is meant to move on its own at a certain time, then the timing of the left shuttle relative to the back tension arm matters a great deal. If the back tension arm is meant to be pushed by the shuttle, then the timing shouldn't matter, but the default position of the tension arm would (whether it's at an angle where it can be pushed, or where it's at an angle where it will jam). Knowing which is the case will give a lot of insight into what's actually going on when the unit jams! This is the question I most want to know the answer to, so if anyone knows how it's meant to operate in the first place, I would greatly appreciate a direct answer.