jwp@larry.sal.wisc.edu (Jeffrey W Percival) (11/02/89)
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.). I guess I'm looking for a knowledgable TV person who I can correspond with, who can suggest things to look at. I'd appreciate any help! -- -Jeffrey W Percival (jwp@larry.sal.wisc.edu)
myers@hpfcdj.HP.COM (Bob Myers) (11/04/89)
>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.
cook@stout.ucar.edu (Forrest Cook) (11/06/89)
In article <107@cupcake.sal.wisc.edu> jwp@larry.sal.wisc.edu (Jeffrey W Percival) writes: >I have a 22-year old Panasonic TR-205 B/W TV (transistors, no tubes). ... >Now I have more subtle problems: mainly, a very >grainy picture. Very white-noisy. Otherwise, stable (no roll, etc.). That sounds like the first RF amp stage in the tuner is dead. I would suggest removing the tuner and replacing the transistor that is nearest to the antenna terminals. Be prepared for some micro surgery, The parts are usually crammed in pretty tight. One word of caution: be careful not to bend the coils or you will detune the tuner. Good Luck ^ ^ Forrest Cook - Beware of programmers who carry screwdrivers - LB /|\ /|\ cook@stout.ucar.edu (The preceeding was all my OPINION) /|\ /|\ {husc6|rutgers|ames|gatech}!ncar!stout!cook /|\ /|\ {uunet|ucbvax|allegra|cbosgd}!nbires!ncar!stout!cook
barry@hprmokg.HP.COM (Barry Fowler) (11/07/89)
cook@stout.ucar.edu (Forrest Cook) writes: In article <107@cupcake.sal.wisc.edu> jwp@larry.sal.wisc.edu (Jeffrey W Percival) writes: >I have a 22-year old Panasonic TR-205 B/W TV (transistors, no tubes). ... >Now I have more subtle problems: mainly, a very >grainy picture. Very white-noisy. Otherwise, stable (no roll, etc.). That sounds like the first RF amp stage in the tuner is dead. I would suggest removing the tuner and replacing the transistor that is nearest to the antenna terminals. Be prepared for some micro surgery, The parts are usually crammed in pretty tight. One word of caution: be careful not to bend the coils or you will detune the tuner. --------------- I agree, check the RF amp. One other possibility is an IF amp. transistor or the obvious, any small wires connecting to the tuner (especially the balun wires).