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-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Colin Herbert via Groups.Io
Sent: 08 December 2018 14:42
To: [email protected]
Subject: [TekScopes] 466 Channel 2 problem

Hi,

I have been faffing about with a 466 with a channel 2 problem for a few weeks, and though I might eventually sort it, I thought I would consult the experts and possibly save a bit of time.

The scope came with a non-operational delayed time-base and an intermittent graticule illumination light. I have fixed both of these now, but the channel 2 problem is bugging me. The scope works on channel 1 alone fine, so it can't be anything after the diode-switching circuitry (can it?), but channel 2 doesn't display normally. If I push the beam-finder switch, I see channel 2, but the position control does nothing. If I use a slow time-base setting and switch to "alternate", I can see channel 1 and there is a period when channel 2 would be displayed, but no channel 2 shows. I have checked voltages and signals for channel 2 from the end of the attenuator through to the diode channel switching (possibly not comprehensively) and mostly cannot see anything untoward. I have also checked to see that the "position" control does change the voltages on the two nominal +2.8V rails, but rather asymmetrically (-0.6 to +2.8V on one rail and 2.79 to 2.8V on the other). I am suspecting that there is something wrong with the "position" control circuitry, but changing Q262 didn't solve the problem.

I also noted that I cannot trigger the time-base from channel 2.

Am I missing something obvious? I would like to get this 466 working, as it is one of three that I have, one of which has already become a parts-donor. I might even try fixing the other one sometime.
TIA, Colin.