Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!usc!ucsd!ucbvax!hplabs!hpfcso!hpfcdj!myers
From: myers@hpfcdj.HP.COM (Bob Myers)
Newsgroups: sci.electronics
Subject: Re: Help needed troubleshooting B/W TV
Message-ID: <17660030@hpfcdj.HP.COM>
Date: 3 Nov 89 19:56:55 GMT
References: <107@cupcake.sal.wisc.edu>
Organization: Hewlett Packard -- Fort Collins, CO
Lines: 28

>I have a 22-year old Panasonic TR-205 B/W TV (transistors, no tubes).
>I am trying to get it working again, and fixed a problem in the
>vertical deflection circuitry (bad capacitor trashing the vertical
>sawtooth voltage).  Now I have more subtle problems:  mainly, a very
>grainy picture.  Very white-noisy.  Otherwise, stable (no roll, etc.).

Not enough signal?  If you have access to a TV RF signal generator, check and
see if increased levels of input signal help clean up the picture.  The
deflection circuits can usually lock in on a weaker signal than is needed
for a noise-free picture.  My guess is your problem is in the tuner/RF amp
stages, with the next most likely culprit being a poor connection to the
video amp.  One VERY easy thing to look for, now that I think about it a
moment, would be a loose connection in the coaxial cable which probably runs
from the tuner to the video amp, or a bad cable here.  Look for an RCA
phono jack or similar on the tuner (which is probably in a metal can),
labelled "VIDEO" or something like that.  Give the cable a shake and watch
the results.

You're 90% of the way there; having a picture at all says that the deflection,
power supply, and high voltage supply are all OK, and I'm assuming the
sound is OK too since you didn't mention it.  That leaves you with the
tuner -> video amplifier chain as the only things left to check out.
Good luck!


Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
myers%hpfcla@hplabs.hp.com               |  sentient life-form on this planet.