Magnavox , dim raster, bright retrace lines.

[Tom Knowles]

Ch 27x602-00BB
Voltages on all 3 Cathodes of CRT are high, in the order of 190 volts.
Similar chassis print shows about 135 volts. Acts as if screen control
is turned too high but this voltage is ok (variable with screen
control.)
Sound indicates that channels are changing and video is scoped ok at
output of video amp.
Need suggestions, thanks.
Tom

 

[Ol' Duffer]

Not having schematic handy (it's at work, I'm at home), my first
guess is open resistor on CRT board - supply resistor for drive
IC has been known to blow open on some models. Low value, 1 Ohm
or 10 Ohm (I forget). Exact value not critical, it's really a
fuse.

 

[Bill S.]

High cathode should turn the beam off, hmmm....
There is a control grid that connects to ground through a
1.5K resistor R5 or R25 depending on which CRT board you have.
I've never seen one bad, but it's easy to check.

Weak 200V supply commonly causes bright retrace (R460, D460,
C461) but I'd have expected lower cathode voltages if that
were the case.

Otherwise dunno - runaway high voltage, gassy tube, other?

 

[Tom Knowles]

Thanks for the reply.
I dusted off my scope, and observed excellent signal pulses and the 3
color output trnsistors on the crt socket at the emitters. Went to the
collectors, no signal pulses. Removed picture tube PC board and had
very strong pulses on the collectors. I surmized from that the picture
tube was bad.
Tom