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+--- Thread: HP9100 display issue (/thread-20512.html)
HP9100 display issue - dbrb2 - 09-17-2023 01:28 PM
Hi
I have an HP9100 calculator
It doesn't get turned on very much. However, when used about a year ago it was fine.
Last week I turned it on and the CRT lit - but didn't seem to be scanning properly. You could see that keystrokes were displaying, but all three lines were lit all the time, making it almost impossible to differentiate what you had typed.
Today I turned it on and the CRT didn't light up at all.
Are there any useful pointers for where I might start if I wanted to troubleshoot this? CRTs scare me a little!
Photos below:
https://photos.app.goo.gl/qaVQqvqFojPZsmmh8
RE: HP9100 display issue - John Garza (3665) - 09-17-2023 09:06 PM
Well... all three lines are supposed to be lit all the time. It's a display of the x,y, and z registers, each on it's own line. Are you saying it was NOT doing that before?
Also, I've found the voltages drift over the years, causing the display to very slowly light (minutes), or never. The adjustment is in the top right area when you have the machine open.
-J
RE: HP9100 display issue - dbrb2 - 09-17-2023 09:54 PM
Ah - I should have described it better. Last night, it looked like every possible digit on every one of the three row was lit at all times. As you performed calculation steps, you could just about discern the "correct" lines becoming slightly brighter.
I had the case open, though didn't touch anything, but this morning the display is entirely blank.
RE: HP9100 display issue - teenix - 09-17-2023 10:24 PM
Failing electrolytic capacitors maybe? Any original ones are pretty old by now and probably due for replacement. As a quick check you can look for bulging out of shape or leaky ones.
If it is a CRT issue it could fall into the realm of a TV repairman, which might be as scarce as the 9100 these days. The 9100 service manual has some info on this.
cheers
Tony
RE: HP9100 display issue - John Garza (3665) - 09-18-2023 01:44 AM
OK, first try adjusting the intensity control of the CRT - again, in the top right. Look for holes in the metal box attached to the top case. Be sure to use an insulated screwdriver. Since you said the correct segments are a little brighter - this may work by forcing more contrast. Otherwise, you need to dig a little deeper. The digit segments are always scanned. The electron beam is turned off/on at the appropriate times to render a digit. This is controlled by a little card A21, also in the area. The voltage adjustments I mentioned earlier are here, as well as a few capacitors that could be replaced.
-J