[time-nuts] FW: HP-5372A operation with no CRT display.

[Lester Veenstra]

Ed:
   I see what appear to be good voltages from the mothor board into the A17
video driver board, that is Gnd, +12VDC, V Sync, HSync, and video
(Intensity)

Have  a possibly good A17 board, on the bench along with a CRT, removed from
instrument. 

Am testing voltages, waveforms, and Electrolytic Cap values for base line.
It functions with just +12V drive from bench supply.  I have a raster scan
that varies in intensity with voltage level (0-5v) applied to video input.


Have two more (not good) boards, with some known bad caps, that then can
then be repaired to the baseline.    Will then try A17 and CRT on the 5372A
itself.

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y
lester at veenstras.com

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-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at lists.febo.com] On Behalf Of ed
breya
Sent: Tuesday, June 30, 2020 4:40 PM
To: time-nuts at lists.febo.com
Subject: Re: [time-nuts] FW: HP-5372A operation with no CRT display.

Looking back at the OP, it appears the display is at least partially 
working, since there is some HV to light a dim spot on screen. I don't 
know what this display looks like inside, but imagine it's one or two 
small boards mounted open-frame on the CRT mechanical assembly, and 
connected to the instrument by one or two cable/connector assemblies. It 
should be possible to remove the whole thing onto a bench, and run it 
out in the open for better access.

The first thing to do is close inspection, looking for any obvious 
problems like puffy or leaky capacitors and burnt parts, loose/broken 
connections, and possibly fuses open. Power supply problems are the most 
likely culprits, so if you can figure out the internal power 
distribution at least somewhat, you can make some measurements. These 
kind of units likely run on a single bulk supply at a standard voltage 
like +12 (most likely since most magnetic raster CRTs use 12V heaters) 
or +24, and you should be able to find out from the schematics for the 
rest of the system.

Are the signals in the interconnections labeled? If so, the power should 
be identified, and also try to figure out what each signal is supposed 
to do. You already know the sync and video, etc, but also look for 
anything else like an enable or standby signal. What I'm getting at here 
is that depending on the overall supply architecture, when the 5372A is 
in standby (keeping the OCXO on) it could be that a lot of stuff is 
actually powered, but disabled. Related to this, is there a GPIB or 
other command that can turn off the display and lock out the front panel 
when in remote-only mode? If there is some form of on/off provision, a 
signal failure here could shut it down even if the rest is OK.

There are lots of possibilities, but it narrows it down a lot if you can 
proof the supplies and external controls.

Ed

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