Quote:
Originally Posted by Jon F
The H and V holds are now unstable though, very touchy. Also, seeing some retrace lines. I am going to check some resistors near the brightness control for the retrace lines. I am also going to look at replacing some tubes that hopefully will help the hold issue.
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These sets were kinda unstable when new.
If you have a scope, check to see if the sync separator is working properly. If not check for voltages off spec in that circuit. Try substituting the sync tube.
Oh the retrace issue, remember this set is electrostatically swept and therefore you don't have the usual big voltage signals being generated that normal B&W TVs use to key the blanking. In fact, the high voltage oscillator is not even running on the horizontal sweep frequency in this set! To the best of my knowledge there is no blanking in this set, other than the video itself.
All the Motorola 7's and most other 7 inch electrostatic sets have iffy blanking. If memory serves me correctly the 8BP4 you have uses the same electron gun as the 7JP4 with simply a larger bulb on the other end and the 8's seem to be a bit more critical on retrace than the 7's.
I assume that you have replaced all the 6KV capacitors in the set and the paper capacitors in the video output stage, especially the one going to the cathode of the CRT. Make sure the 100K resistor going from the filament of the 1B3 to the anode (pin 6) of the CRT has not increased in value. Check the value of the 150K resistor between the control grid of the HV Osc. and the ground. (That is High Voltage osc. and not the Horizontal Sweep osc.)
Your next step is to adjust the high voltage. To do this on this set, turn the set off channel and and lower the brightness slightly. Using a plastic stick gently slide the gimmick (the spring around the belly of the 1B3/8016) up and down while adjusting the screen for the maximum brightness. After this, readjust the focus. Now feed a signal into the TV and adjust the brightness and contrast the best you can to get rid of the retrace.
James