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HP 853A - no CRT display at all - troubleshooting help needed

David Feldman All Messages By This Member #110709 I have HP 853A mainframe with HP 8557B (the 75 ohm version) plug-in. The 853A CRT has no display light output at all, at any intensity/focus setting. If I plug an external scope set to X-Y display into the rear X-Y outputs, the analyzer plug-in appears to be functioning normally (and the same plug-in works fine in another 182 mainframe.) I've downloaded manual 00853-90010 and checked DC voltage test points on A3 (all were in spec), then went to section 5-13, and with a Tektronix P6015A 40 kV 1000:1 scope probe, I verified HV cathode (test point A4TP1) is close to the voltage marked on the module (-2467 volts). Step 5-13-8 it tells me to measure A6TP2 (which I think is a typo; there is a test point on A4 called A4TP2 and after this test point is checked, instructions tell me to put the cover of the HV section back on.) A4TP2 measures 27.3 volts at any setting of the front panel intensity control (the text in section 5-13 step 8 specifies 30.0 +/- 0.2 volts, and tells me what to do if the voltage is too high, but not too low.) I tried setting the 8557B to manual sweep to get a dot on the display, but no light seen. As the manual at this point anticipates that the CRT should be emitting light (and is mostly worried about too much intensity), I think I'm not looking in the right place. Any idea where to look next? Thanks!
David Feldman All Messages By This Member #110723 Headed over to section 8 (service) - troubleshooting - general. Paragraph 2 describes how to check analog circuitry; I temporarily removed A7 as instructed (what remains is an analog oscilloscope function) and still get no light output. A7 was put back into place. Went back to re-measure the display regulator boad test points - the +158V test point actually reads about +168V, and it's status LED (DS3 I think - the scan isn't very good) is not lit. The other regulated and unregulated outputs (+/- 15V, 5V, 11V) are all correct. Tks, Dave
paulswed All Messages By This Member #110726 Check several other voltages and all will lead to no display. X or Y axis way off screen Blanking hard blanked off. I have run into all of these and the great news is its easy to find the issue when these are really bad. Also sometimes its useful to turn off all lights in a dark room any hint of a glow? Top bottom left right brightness all teh way up. Is there a beam finder? Good luck Paul
Ken Nener All Messages By This Member #110728 Dave: I have a couple of these myself. I suggest checking the deflection amplifier final stage resistors -- they went way off-value/open on both of my units. Check both horizontal and vertical. Also - check ALL of the high-voltage multi-megohm resistors associated with the various CRT grid voltages. These are right at the CRT itself. These commonly go open in older units and will lead to no display. You may need to buy a 10 or 20 megohm resistor to put in parallel so you can measure the higher resistance parts (i.e. above 20 megohms). Generally you will see the same failures over and over if you fix enough of these older HP displays. One last thing - makes sure your lower-voltage DC rails are all good - I had one of these fail on a unit as well. At least make sure the status LEDs are all lit. BR, Ken toggle quoted message Show quoted text -----Original Message----- From: [email protected] <[email protected]> On Behalf Of David Feldman via groups.io Sent: October 7, 2020 9:57 PM To: [email protected] Subject: [HP-Agilent-Keysight-equipment] HP 853A - no CRT display at all - troubleshooting help needed I have HP 853A mainframe with HP 8557B (the 75 ohm version) plug-in. The 853A CRT has no display light output at all, at any intensity/focus setting. If I plug an external scope set to X-Y display into the rear X-Y outputs, the analyzer plug-in appears to be functioning normally (and the same plug-in works fine in another 182 mainframe.) I've downloaded manual 00853-90010 and checked DC voltage test points on A3 (all were in spec), then went to section 5-13, and with a Tektronix P6015A 40 kV 1000:1 scope probe, I verified HV cathode (test point A4TP1) is close to the voltage marked on the module (-2467 volts). Step 5-13-8 it tells me to measure A6TP2 (which I think is a typo; there is a test point on A4 called A4TP2 and after this test point is checked, instructions tell me to put the cover of the HV section back on.) A4TP2 measures 27.3 volts at any setting of the front panel intensity control (the text in section 5-13 step 8 specifies 30.0 +/- 0.2 volts, and tells me what to do if the voltage is too high, but not too low.) I tried setting the 8557B to manual sweep to get a dot on the display, but no light seen. As the manual at this point anticipates that the CRT should be emitting light (and is mostly worried about too much intensity), I think I'm not looking in the right place. Any idea where to look next? Thanks!
David Feldman All Messages By This Member #110740 So far - no hint of a glow, even in complete darkness. There's no beam finder control; there are position trimpots on the front which didn't bring anything into view. Verified (with power off) filament continuity (temporarily disconnect filament lines from HV board to CRT). No sign of residual light during power down. Also, sometimes when I turn on old-style oscilloscopes I hear a "crackling" sort of sound (as the HV comes up); no sign of this here. Status LEDs are lit except for the LED reflecting the 158V output of the display section power regulator - the test point where that LED is located is showing ~168V (supposed to be 158V.)
J Mcvein All Messages By This Member #110741 I had a 853A CRT slowly lose its vacuum.? The deflection amps roasted as the current increased until the tube no longer showed a picture/trace.? -J- toggle quoted message Show quoted text -----Original Message----- From: "David Feldman via groups.io" <wb0gaz@...> Sent: Thursday, October 8, 2020 11:59am To: [email protected] Subject: Re: [HP-Agilent-Keysight-equipment] HP 853A - no CRT display at all - troubleshooting help needed So far - no hint of a glow, even in complete darkness. There's no beam finder control; there are position trimpots on the front which didn't bring anything into view. Verified (with power off) filament continuity (temporarily disconnect filament lines from HV board to CRT). No sign of residual light during power down. Also, sometimes when I turn on old-style oscilloscopes I hear a "crackling" sort of sound (as the HV comes up); no sign of this here. Status LEDs are lit except for the LED reflecting the 158V output of the display section power regulator - the test point where that LED is located is showing ~168V (supposed to be 158V.)
David Feldman All Messages By This Member #110761 Thanks, that is good to know (in genera!) - I'll take a look at the waveforms from the test points on A6 (XYZ amplifier board) which drive the CRT and see if that suggests anything. Unfortunately, no spare 853A to use for comparison.

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