I would appreciate some insights from folks with VCR repair experience;
I have a JVC HR-S7000U S-VHS machine with chroma problems and I do not
yet have the service manual. I have downloaded a number of other
JVC HR-Sxxxx S-VHS service manuals (from eserviceinfo.com) but these
are for much newer machines and I doubt the chroma electronics is
similar to mine; the only adjustments in these newer machines are
gain related except for subcarrier oscillator frequency settings. There
aren't any phase or linearity adjustments.

Please look at these photos of signals from my VCR:

1. This is a vectorscope display of the S-Video output of the VCR when
playing full-height color bars from VHS tape (not recorded on this
machine, but on another VCR and verified for purity and level)

ftp://www.cybertheque.org/pub/tmp/HR...playback-1.jpg

Note how the magenta and cyan bars are way off target.

2. These three images are of Patrick Stewart in "Encounter At Farpoint"
from the Paramount tape; note the incorrect uniform color, the lavender
tinges on his lips and poor flesh tones and white balance:

ftp://www.cybertheque.org/pub/tmp/HR...farpoint-1.jpg
ftp://www.cybertheque.org/pub/tmp/HR...farpoint-2.jpg
ftp://www.cybertheque.org/pub/tmp/HR...farpoint-3.jpg

Short of simply replacing entire subassemblies, what typically have
any of you who repair and set up these machines done in the case of this
sort of problem? Do any prosumer S-VHS machines have phase, gain and
linearity adjustments in the chroma processor section? What about
chroma noise?

I imagine that for VHS playback, the machine uses the "color-under"
encoding system; have any of you effected component level repairs
on earlier machines (with discrete oscillator, mixer, and modulator
stages) to fix chroma problems and have notes involving bench
instrument setups and measurements for alignment when the service
manual is silent on these topics?

Thanks for any insights,

Michael

"msg" wrote in message
...
I would appreciate some insights from folks with VCR repair experience;
I have a JVC HR-S7000U S-VHS machine with chroma problems and I do not
yet have the service manual. I have downloaded a number of other
JVC HR-Sxxxx S-VHS service manuals (from eserviceinfo.com) but these
are for much newer machines and I doubt the chroma electronics is
similar to mine; the only adjustments in these newer machines are
gain related except for subcarrier oscillator frequency settings. There
aren't any phase or linearity adjustments.

Please look at these photos of signals from my VCR:

1. This is a vectorscope display of the S-Video output of the VCR when
playing full-height color bars from VHS tape (not recorded on this
machine, but on another VCR and verified for purity and level)

ftp://www.cybertheque.org/pub/tmp/HR...playback-1.jpg

Note how the magenta and cyan bars are way off target.

2. These three images are of Patrick Stewart in "Encounter At Farpoint"
from the Paramount tape; note the incorrect uniform color, the lavender
tinges on his lips and poor flesh tones and white balance:

ftp://www.cybertheque.org/pub/tmp/HR...farpoint-1.jpg
ftp://www.cybertheque.org/pub/tmp/HR...farpoint-2.jpg
ftp://www.cybertheque.org/pub/tmp/HR...farpoint-3.jpg

Short of simply replacing entire subassemblies, what typically have
any of you who repair and set up these machines done in the case of this
sort of problem? Do any prosumer S-VHS machines have phase, gain and
linearity adjustments in the chroma processor section? What about
chroma noise?

I imagine that for VHS playback, the machine uses the "color-under"
encoding system; have any of you effected component level repairs
on earlier machines (with discrete oscillator, mixer, and modulator
stages) to fix chroma problems and have notes involving bench
instrument setups and measurements for alignment when the service
manual is silent on these topics?

Thanks for any insights,

Michael

Try warming electrolytic capacitors in the chroma stage with a hair drier
and using freezer spray to locate the fault to a single or group of
components.
JVC recorders seem to have batches of capacitors coloured Red or Green that
show batch faults.
Give it a try a few seconds with a hair drier can save hours of time fault
finding.
Cheers John.