NEC JB-902ME-5 green monochrome monitor bad picture fix?

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NEC JB-902ME-5 green monochrome monitor bad picture fix?

Postby anetanel » 2018-7-10 @ 06:20

Hey guys.

I got a NEC JB-902ME-5 green monochrome monitor, with composite input. It turns on and the picture is quite bright, but it does not seem to "sync".
I hooked it to several outputs, including the Atari 800XL in the picture, but although I can see that the signal is getting through, the display is always fuzzy. I played with all the knobs and switches in the front and back, but nothing I did fixed the issue.
What could be the possible reason?

Also, I was not able to find any mention to this specific monitor on google...

Thanks :)
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NEC JB-902ME-5
2016-12-31 22.44.30.jpg
NEC JB-902ME-5
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Re: NEC JB-902ME-5 green monochrome monitor bad picture fix?

Postby 133MHz » 2018-7-10 @ 17:31

Which knobs are on the back? It looks like the horizontal oscillator frequency is off, requiring adjustment of the H.HOLD or H.FREQ control.
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Re: NEC JB-902ME-5 green monochrome monitor bad picture fix?

Postby anetanel » 2018-7-11 @ 06:15

I tried all of 5 of these knobs..
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Re: NEC JB-902ME-5 green monochrome monitor bad picture fix?

Postby ATauenis » 2018-7-11 @ 08:19

Does something changing on H Hold knob adjusting? Also HIGH/75 Ohm switch might be useful, did you tried it? For devices with TV out the normal mode is 75 Ohm, not High (1k Ohm).
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Re: NEC JB-902ME-5 green monochrome monitor bad picture fix?

Postby anetanel » 2018-7-11 @ 14:37

Well, apparently I was simply too gentle.
The H Hold knob gave some resistance so I thought it was turned all the way. Apparently it wasn't!
Gave it (fearfully..) some extra turns and the picture stabilized!
After a year and a half from testing this monitor for the first time, it finally came back to life :)
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Re: NEC JB-902ME-5 green monochrome monitor bad picture fix?

Postby 133MHz » 2018-7-11 @ 21:50

Nice! Glad you got it working, love these tiny green monitors :-)
On many of these 'TV-type' monochrome displays the horizontal hold control is actually a variable inductor (instead of a potentiometer) where a ferrite core is being slid in and out of a coil, hence the knob can be turned many times without hitting a mechanical stop.
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Re: NEC JB-902ME-5 green monochrome monitor bad picture fix?

Postby anetanel » 2018-7-11 @ 21:54

The next step is to find some way to hook it up to my AT clone PC.
I got there a card with MDA output, and as far as I know the signals arn't compatible.
I was able to get both PAL and NTSC work on this display, so I figured I may try to hunt for a CGA card with composite output.
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