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NEC Multisync APC-H4311 and JC-1401P3A

J

Jonno

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Joined
Mar 25, 2024
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Hi Team, I have an NEC Multisync APC-H4311 that is showing abnormal brightness to the point of being unusable. It's paired to an NEC APC-IV PowerMate 1 (AT clone). Before diving deep to resolve I tried sourcing service manuals etc but there is very little out there about it. It does appear almost identical to the NEC JC-1401P3A for which there is a ton of info available. Are these indeed the same monitor or as near the same so as not to worry? Any gotchas I should look out for?

Thanks in advance.
 

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  • APC-H4311 Rear.jpg
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  • APC-H4311 Controls.jpg
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Further research indicates the two monitors have the same chassis and the JC-1401P3A service manual I've located describes the internals of the H4311 pretty well. I'm going to focus on the power supply as the primary culprit - probably electrolytics drifting out of spec. Will report back when I can.
 
Thanks heaps, jafir. The monitor service manual I found is linked from here https://crtdatabase.com/crts/nec/nec-jc-1401p3a
Slightly clearer scan of the document you provided but for the P3A. The bitsavers one is for the P3E. Presumably its either a slightly earlier version or a reference to the supply voltages where each monitor would be distributed (AC 120V 60Hz vs AC 220V-240V 50/60Hz). Also some of the board numbers vary slightly but essentially the same monitor. I'll put together some notes of the differences I find inside the APC-H4311.

Cheers.
 
Oh, unfortunatelly archive.org is completely down due to hacking attacks these days. Hope they come back. Me too, I have a working JC-1401P3A monitor, a pretty good one able to display everything between PAL/NTSC in RGB (Amiga, Atari ST), ST-High, CGA, EGA, VGA, Super-VGA, Atari Falcon inclusive it's strange Interlace modes up to 800x600 in 50...60...70 Hz)
 
Looks like archive.org is intermittent - attached is the JC1401P3A manual downloaded from them a couple of days ago.
 

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  • Monitor JC1401P3A Service Manual.pdf
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Hi Candido, welcome to the forums.

When I connect the APC-H4311 monitor to a video card, regardless of the brightness/contrast or input mode settings, the image is visible but difficult to see due to very high white brightness across the whole screen. Over the next minute the screen gradually becomes even brighter so that the image cannot be seen at all. I don't leave it turned on any longer in case there are components being stressed to the point of failure. The video card is configured correctly - tested in CGA mode on an IBM 5153 colour display. The 15-pin video cable has also been tested. My starting point will be the power board electrolytic capacitors and cleaning potentiometers.

I welcome any ideas you may have.
 
Jonno said:
Hi Candido, welcome to the forums. fall guys

When I connect the APC-H4311 monitor to a video card, regardless of the brightness/contrast or input mode settings, the image is visible but difficult to see due to very high white brightness across the whole screen. Over the next minute the screen gradually becomes even brighter so that the image cannot be seen at all. I don't leave it turned on any longer in case there are components being stressed to the point of failure. The video card is configured correctly - tested in CGA mode on an IBM 5153 colour display. The 15-pin video cable has also been tested. My starting point will be the power board electrolytic capacitors and cleaning potentiometers.

I welcome any ideas you may have.
Click to expand...
Wow, I've been waiting for this answer for a long time!
 
Page 30 has some advice on finding the cause of abnormal brightness. I would start there. In general, if the brightness is too high, either the screen/G2 voltage is too high, or the cathode voltage is too low.
 
Jonno said:
Over the next minute the screen gradually becomes even brighter so that the image cannot be seen at all.
Click to expand...
Functinality slowly changing over a few minutes as the system warms up is a typical sign of a failing electrolytic capacitor. You might be able to locate the faulty component by carefully spraying compressed air on each electrolytic capacitor, and watching the image for change.
 
A small update. I've disassembled enough of the APC-H4311 to be able to pull out the switching regulator (powerboard) and read the markings on all the other boards. The markings on the boards in the APC-H4311 are the same as those listed in the JC1401P3A, other than the switching regulator.

Board \ Monitor:APC-H4311JC1401P3A
Switching RegPWE-142PWE-107
InterfacePWE-110PWE-110
DeflectionPWE-105PWE-105
ControlPWE-125APWE-125A
LEDPWE-125BPWE-125B
VideoPWE-122PWE-122
CRTPWE-123 PWE-123
Tube370HYB22-TC126 (PN2)370HYB22 (from here)
(Apologies - I couldn't work out how to limit column width)

My initial thoughts are the PWE-142 board is spec'd the same as a PWE-107 - it's output is driving the exact same other boards a PWE-107 would in a JC1401P3A). Of lesser importance is the schematic and picture in the manual look identical.

So the APC-H4311 is effectively the same as a JC1401P3A (a marketing ploy perhaps?)

Now the interesting bit. On the APC-H4311 PWE-142 switching regulator I measured the 85V output rail as 99V and the 24V output rail as 31V. Both slowly increasing as I watch the meter. I should also note this is without a load. Am I right in thinking this is the probable cause of the excessive brightness?

If so, should next steps be to pull the electrolytics in the switching regulator?
 
I should have mentioned earlier that this monitor is not totally unknown to me - it was working when I last used it 20+ years ago. It's just been in storage for that long.
 
These types of power supplies usually don't work properly without a load. I would try measuring the voltages with the power supply connected to the rest of the monitor.
 
Jonno said:
regardless of the brightness/contrast or input mode settings, the image is visible but difficult to see due to very high white brightness across the whole screen.
Click to expand...
This also can happen if the DIP switches of the NEC Multisync's rear side and analog/ttl switch aren't set properly for the video mode. See user manual.
 
andy said:
These types of power supplies usually don't work properly without a load. I would try measuring the voltages with the power supply connected to the rest of the monitor.
Click to expand...
Thanks for the tip, Andy. I measured 23.25V and 82.0V when connected to the rest of the monitor. I'll try working through the manual from p30 as per your earlier suggestion.
 
Thanks for the idea 1ST1. I've checked and double checked the switch settings. To easily access different test modes I'm using two separate machines with graphics cards configured to IBM CGA and IBM EGA modes (and seen in the correct test modes using an IBM 5153 color monitor and other test monitors showing the correct mode). The NEC monitor is configured to TTL and Manual is off. The Text switch in the top control panel is set to OFF. My understanding is this configuration setting allows the monitor to switch to the correct mode itself and makes the dip switches redundant. In the first minute after switching on I can just make out the the correct image before the whole screen gradually becomes too white to see it, regardless of CGA, EGA etc.. Let me know if I've got this wrong.

I did notice something I thought was an unusual "design feature" in relation to the DIP switches and the monitor case markings. The case markings show the DIP switches are OFF when toggled right whereas the DIP itself shows as ON to the right. I don't believe this affects the outcome of the settings I'm using. And if I was to use the Manual switch in the ON position would preference the case markings over the DIP. You just have to be careful when setting the DIP switches when the case is removed...
 

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  • APC-H4311 switch external.jpg
    APC-H4311 switch external.jpg
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  • APC-H4311 switch internal.jpg
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Hi Team, I'm outta here for a few weeks so there won't be any progress reports for a while. Enjoy the peace and quiet. ;-)
 
When you get a chance, post a picture or two of what's on the screen. We might be picturing something different from what you're seeing.
 
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