kevin@horizon.UUCP (Kevin Criqui) (10/11/88)
I am looking for schematics, service manuals, or any advice you have concerning a Motorola model VT71MB-A television set. The date on the chassis is April 12, 1949. The receiver seems functional since there is clear audio. The video, however, is dead. No raster, no high pitched noise from the flyback, no nothing. I haven't tested the tubes yet, but will soon. At least one appears to have leaked. I hope most of them are OK (have you priced tubes lately?) Any help or pointers to help will be much appreciated! Please email responses if possible since this is posted to a number of newsgroups. -- Kevin Criqui \_...sdsu!ncr-sd!horizon!kevin Science Horizons, Inc. \_ kevin@horizon.UUCP 710 Encinitas Blvd suite 200 \_ kevin@horizon.CSS.GOV Encinitas, CA 92024 \ (619)942-7333
telecom@homxc.UUCP (Bob S.) (10/15/88)
In lieu of a schematic, it sounds as simple as no high voltage, not video. Tube testers are virtually worthless, and voltage readings on tube pins are not much help (if you had a scope AND knew what the waveforms were supposed to be, this could be a different story). Anyway, replace the horizontal oscillator first. Still doesn't work? Replace the horizontal output AND the damper. Still doesn't work? Check the horizontal/flyback area for open resistors and shorted caps. Real simple troubleshooting for real simple circuits. If you should restore your high voltage, and the picture is fuzzy, replace the high voltage rectifier tube located in the flyback housing. If you're hell bent on getting a schematic, check local electronic houses for Sam's schematics. More than likely you'll have to get tubes from surplus houses too, since most tubes manufactured today are for audio use. Probably be able to pick them up for 50 cents. Good luck! Bob "I was a teenage TV tech" Schwendel