VCR Gymnast wrote:
: A portable Beta VCR (Toshiba V-X340) from 1985 works perfectly except
: there is no color:
: 1. Pre-recorded color tapes play back in B&W
: 2. Tapes recorded on this VCR play back in B&W on this VCR
: 3. Tapes recorded on this VCR play back in B&W on other known good VCRs
: Therefore, the VCR can neither record nor playback color signals.
: The machine has no switch for B&W/Color and the 3.58 MHz oscillator is
: not out of adjustment. I have checked out all of the Chroma circuitry
: and all measurements are within the range stated in the Service Manual.
Well, just an opinion here but I'd go back and check the measurements again,
you are overlooking something.
Althought I've seen beta's go black and white because of the heads, I only
remember it effecting the playback. Tapes recorded on that machine might
look like crap played on another, but you wouldn't get a "really good" b&w
only picture.
With a machine that old (21 years?) I'm pretty sure there is some kind of
simple color shutdown circuit, a gate from one of the large scale IC's or
even a simple comparator using a transistor or two. Keep in mind back then
those machines were somewhat dependent on the broadcasters cutting the color
pilot off during B&W telecasts so you wouldn't get that blue snow in the
pix.
I hate to say it myself repeatedly but unless that thing has some
sentimental value like was the machine you used record your honeymoon night
with the wife, I can't really see why you are bothering with it.
Even if it says Toshiba on the front, in 1985 it would still be a re-badged
Sony model and if I remember history correctly, those things were a
nightmare to work on, the portables. You didn't give a history of it but I'd
guess it was either dropped or more likely disassembled by someone who
didn't know what they were doing and didn't stuff the guts back in
correctly.
My guess is you are dealing with a hairline crack, probably on one of the
boards that uses the side-sled to hold it in. With the amount of wiring
those machines had, the boards were pretty tightly packed and it didn't take
much to flex them into that graveyard in the sky.
If you insist on repairing it, two suggestions, put the machine on the side
and study the service manual, ignoring their troubleshooting guide, those
were worthless for the most part. Study the schematic, especially around the
chroma circuit. There has to be a measurement point listed that shows a
"color only" or "b/w only" reading. That is going to be the gate. It might
be like 6-8v color and 1v b/w, or the other way around but the point is,
it's a fairly measurable swing between the two modes that any cheap meter
should be able to read.
I can almost guarantee this point is dead as a duck and by mearly tying it
high or low will bring the color back. Chances are it's going to go back to
one of Sony's nearly propritary LSIC's which were as nearly as impossible to
get 15 years ago, so I'd just leave it in color mode.
If you really want to bang your head against the wall with it, pick up one
of those (if memory serves) B&K 1472 ntsc generators, or any ntsc generator
that has a simple bw/color on-off switch. Get that meter or scope out and
start taking measurements cycling back and forth on the generator. Something
is going to stick out like a sore thumb and work backwards from there.
Of course there are as many other likely problems as there are total parts
in the machine, dried caps, defective delay lines, cat ****. My bet is still
on a hairline crack or interconnects, remember chasing those in the
portables more than anything else.
Good luck with it but beta portables are in my top 5 list of stuff that just
should be pitched. Depending where you live you'll be far better off
scrounging around yard sales and surplus places for another one. Not that it
would be in mint shape after all these years but simpler to repair. Alot of
those were packed away in the basement because the batteries were too
expensive to replace or the owner went to vhs after the war between the two
was over.
-bruce