EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Xtremexp on January 18, 2025, 09:33:14 pm
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hello all,
I got a hp 1345a display and it got very strange issue. It displays the vectors quite well but the characters are scrambled . The characters that are displayed are random. To debug, I disconnected the data interface and display goes to calibration mode. in calibration mode, the texts are also scrambled, for an example, at the top it should display "Y=2048" but it shows Y]... so I believe this issue is from display itself.
Had anyone faced similar issue and solved the problem?
(http://1345a_issue.png)
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Just a guess, but...
I've repaired several of the 1345A displays. The most common failure are the 2.2 uF tantalum capacitors (usually yellow cylindrical) on the A1 xyz amp/stroke board. One or more shorts out and takes out one or more of the low voltage power rails (+/-15V). Clearly not the case with your unit.
But once, when I was trying to repair a 1345A, I started lifting one end of each tantalum until the short went away. I replaced the shorted cap and the 1345A sprang to life. However, I saw behavior like you are getting - distorted characters. Turns out that I forgot to solder all the leads of the good capacitors that I had pulled up. Once I did that, everything worked perfectly.
So perhaps you have an open tantalum capacitor.
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Just a guess, but...
I've repaired several of the 1345A displays. The most common failure are the 2.2 uF tantalum capacitors (usually yellow cylindrical) on the A1 xyz amp/stroke board. One or more shorts out and takes out one or more of the low voltage power rails (+/-15V). Clearly not the case with your unit.
But once, when I was trying to repair a 1345A, I started lifting one end of each tantalum until the short went away. I replaced the shorted cap and the 1345A sprang to life. However, I saw behavior like you are getting - distorted characters. Turns out that I forgot to solder all the leads of the good capacitors that I had pulled up. Once I did that, everything worked perfectly.
So perhaps you have an open tantalum capacitor.
Thanks for the direction. I opened the unit and looked around it. It seems that someone already has worked on it :) . I see "BAD" sticker on "U5" PROM (character generator). Do you think it might be bad U5 PROM, if thats the case then I do not have any option as I do not think we can find PROM data now. what do you think?
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I guess a bad U5 might make more sense.
In my bad capacitor case, the display was sort of jittering. Your display appears stable, just wrong. So my original capacitor guess could very well be wrong.