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