Author Topic: Repair of an Hp1345a Display.  (Read 305 times)

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Offline Simon Spiers

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Repair of an Hp1345a Display.
« on: April 24, 2019, 04:56:44 pm »
Is there anyone who could point me in the right direction with thus fault on a HP 1345a display. It was working originally and the sth display intensity started flashing, which I first thought was an HV flashover.
I squirted a few Ics on the A1 board  u15,16 and 25 and this is what happened!
Am i looking at a stroke generator fault or Vector fault? I am close to giving up with this bloody thing!

Offline pbarton

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Re: Repair of an Hp1345a Display.
« Reply #1 on: April 24, 2019, 08:38:36 pm »
Warning: I have no experience of the HP1345A/3562A, however your display reminds me of the Digital Equipment Corp (DEC) GT40 vector display, on which I spent many hours landing the lunar module (a.k.a. moonlander).
Your photo appears to me that your are missing some ‘Z’ blanking as there are far too many lines visible (Z appears to be permanently stuck ‘ON’).
The ‘Intensity Control’ U25 appears to be a good place to start. Is the O/P on U25 switching or is it stuck?
Furthermore, you mention "intensity started flashing" which could also indicate a problem with the Z circuit.
« Last Edit: April 24, 2019, 09:00:47 pm by pbarton »
 

Offline Tomorokoshi

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Re: Repair of an Hp1345a Display.
« Reply #2 on: April 24, 2019, 09:01:15 pm »
Another options is to replace it with an LCD:

http://www.simmconnlabs.com/
 

Offline Simon Spiers

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Re: Repair of an Hp1345a Display.
« Reply #3 on: April 24, 2019, 09:02:32 pm »
Thanks for your rely. I have been probing around and found one op amp is dragging the -15 V rail down and is shorting the output of its associated DAC (u16 & u18). So it looks live to op amp has failed. I'm hoping the intensity control chip is good as it is not available from anywhere I can find.

Offline Simon Spiers

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Re: Repair of an Hp1345a Display.
« Reply #4 on: April 24, 2019, 09:04:52 pm »
I~ have considered replacing with a LCD display. But as the 3562a is far from reliable, i can't justify the expense.

Offline duak

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Re: Repair of an Hp1345a Display.
« Reply #5 on: April 25, 2019, 09:16:49 pm »
I would check for bad tantalum caps - here's one experience: https://whatever.sdfa3.org/tag/hp1345a.html

I'd then check the Z-axis drive stuff on schematic 5 (figure 8-14).  The cathode and first grid of the CRT are 2500 V below circuit common so you have to be careful with probing.  I'd expect Q4-Q6 or something around around them to be shorted or open.

Cheers,
 


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