Newsgroups: sci.electronics
j...@wdc.sps.mot.com
Does anyone know what it takes to fool a VCR into thinking
that there is a tape in it and therefore allowing it to play
etc. My VCR's take up spool seems to have died and I cannot
tell with a tape in it if the motor is functional or not. There
is no access (that i can see) from the back. I would hate to
trash the VCR without first taking it apart ;-)
Any help, info etc would be welcome.
Regards
jas
Mike
Well, with the information you've given, I'm going to have to make
some assumptions, the main one being the type of machine you're
using: I'll assume a VHS (or S-VHS) mechanism. I'll also assume
that you've got the top off the machine.
Right, inside the machine you will find the head drum - don't touch
the heads! With the cassette loading flap towards you and the
machine right-side-up, the mechanism will probably look a bit like
this (top view) :-
**** o = Guide post
^ ** ** ^ ^ = V-notch
* Head * E = erase head
* * AC = audio/control head
E * Drum * o B = bulb/LED
o ** ** AC P = photodetector
**** o
P P
+-----------o-o--o-----------------------+
| |
| B |<----- This is the cassette case
| |
The VHS machines are arranged so that as a tape is inserted, the
light path between the bulb and the photodetectors is broken. This
is sensed and used to enable the rest of the mechanism. The clear
leader at the beginning and end of cassettes allows light to reach
the photodetectors again, but because of the tape motion, only one
detector will be illuminated at a time, the left hand detector when
the end of tape is reached and the right hand detector at the
start. This enables the auto-stop (and/or auto-rewind) functions to
operate.
This should tell you how to fool the VHS machine into thinking that
it has a tape in - simply cover the bulb (or the photodetectors)
with some insulation tape. However, there are four things to watch
out for. First, the machine will expect the cassette lift to be in
the "down" position - you'll have to figure out how to fool this
part of the machine yourself since it varies a lot from machine to
machine.
The second thing is safety related. BE CAREFUL. Bits of the
machinery may move suddenly and quite quickly, especially on modern
decks. It can hurt if your finger gets caught by the loading arm -
I know, I've tried it. I wouldn't recommend it as a fun way to
spend an evening. Unless you're confident that you know what's
going on, leave it to the professionals.
The third item is also safety related. The power supplies have live
mains on them, and not all are well designed. Some are quite safe,
and will not allow fingers to accidentally touch live contacts.
SOME ARE LETHAL. Use an isolating transformer unless your certain.
The final thing is the old addage "if you don't know what it does,
don't fiddle with it". The mechanism of a VHS machine is a piece of
precision machinery. The chances of you setting it up correctly
without the correct test equipment is just about zero, and a full
realignment is costly and time-consuming. The same applies to the
electronics. Don't just stick a screwdriver in and hope: get the
service manuals.
Having said all that, if it does prove to be the motor at fault,
changing it shouldn't be too hard. Most fall out of the machine
with a couple of screws and can be replaced as easily - normally no
realignment is needed afterwards. While you have the machine in
bits, check the state of any rubber parts - these deteriorate and
can start to stretch/slip causing all sorts of annoying faults
(including tape-chewing). Take care with the brake-band however -
it does wear out, but the back-tension and head-switching point will
need to be reset afterwards: a job for the professionals.
Good luck,
--
Mike Ellis, Darwin College, The University, Canterbury, Kent, England, CT2 7NY.
********* Views expressed are my own and in no way represent *********
********* the views of any past or present employers. *********
Paula Stockholm
>
> Does anyone know what it takes to fool a VCR into thinking
> that there is a tape in it and therefore allowing it to play
> etc. My VCR's take up spool seems to have died and I cannot
> tell with a tape in it if the motor is functional or not.
There are clear plastic gizmos that can be used instead of a tape.
Price is $15 at an electronics supply.
What has probably happened is that little rubber wheel has dried out
and no longer has the friction to turn the take up reel. Replacement
tires are less than $10.
On SOME brands you can remove the top and front covers and then undo
two screws holding the cassette basket to the metal frame. Then
after removing the basket and placing it on a magazine or something
to insulate it from the circuit traces, you can stick a tape in it
and watch the activity in the exposed VCR.
On the more recent models, the reels are gear-driven and the cause
lies deeper in the VCR.
Tell me Make and Model.
--
* * * * * * * * * * * * * * * * * * * * * * * * * * *
* pa...@nlbbs.com *
* Paula Stockholm Cumberland, Maine USA *
* * * * * * * * * * * * * * * * * * * * * * * * * * *