Preferred way of substituting TFT for CRT Monitor?

Wed Jan 20 04:25:59 CST 2016

> ------------------------------

> Message: 8

> Date: Mon, 18 Jan 2016 15:39:38 -0500

> From: "js at cimmeri.com<mailto:js at cimmeri.com>" <js at cimmeri.com<mailto:js at cimmeri.com>>

> To: General Discussion: On-Topic and Off-Topic Posts

>            <cctalk at classiccmp.org<mailto:cctalk at classiccmp.org>>

> Subject: Re: Preferred way of substituting TFT for CRT Monitor?

> Message-ID: <569D4D8A.4080505 at cimmeri.com<mailto:569D4D8A.4080505 at cimmeri.com>>

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>

> . . .

> You need a monitor (or converter) that supports 25khz.  Here's the extent of my own research:

>

> 25khz 640x400 SOG monitors

>

> LCD

> - NEC LCD1510+ (not tested)

>

> - NEC LCD1810 (LA-1831JMW-1)

>    Mac + PC -- fair performance, poor scaling.

>    HP 300/98543 -- works, but banded background cannot be completely

>       faded to black (I got rid of my 1810's for this reason).

>

> - Viewsonic Vp150

>    HP300/98543 -- works well, great background, colors only fair.

>

> - Viewsonic VP181

>    HP 300/98543 -- not perfect but can be adjusted ok.

>      banded background *can* be faded to black.

>

> - J.

> ------------------------------

ah, this seems to become difficult...

Thanks for the data and recommendations. I will have a look at low H-freq. monitors on ebay, maybe I have to revert to an old, heavy and large CRT.  I see that many  Viewsonic TFT monitors start at 24kHz.

I also found

http://www.ebay.de/itm/Gonbes-GBS-8200-CGA-15kHz-EGA-25kHz-Arcade-JAMMA-PCB-to-VGA-Video-Konverter-/111506569501

The technical data (http://www.extremehardware.webspace.virginmedia.com/ebay_images/GBS-8200.pdf) says:

CGA / EGA - Auto Scan:

14.5 kHz - 16.5 kHz

23.5 kHz - 25.5 kHz  <<<< this may fit the HP card?

3 0.5 kHz - 32.5 kHz

Martin

> ------------------------------

> Message: 9

> Date: Mon, 18 Jan 2016 21:07:27 +0000

> From: tony duell <ard at p850ug1.demon.co.uk<mailto:ard at p850ug1.demon.co.uk>>

> To: "General Discussion: On-Topic and Off-Topic Posts"

>            <cctalk at classiccmp.org<mailto:cctalk at classiccmp.org>>

> Subject: RE: Preferred way of substituting TFT for CRT Monitor?

> Message-ID:

>            <A8192EF71C5C4946A240D25EDC8F9448027E4311 at EXMBX15.thus.cor<mailto:A8192EF71C5C4946A240D25EDC8F9448027E4311 at EXMBX15.thus.corp>

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>

> > indeed this machine has a 98204B video board (intended to work with a 35721

> monitor,

> >  which I don't have). I have not yet found the specs for its composite signal.

>

> It is normal composite video voltage levels with faster-than-normal horizontal scan rate.

> If you have a frequency counter (or something that can be used as one, then put the 98204B

> text board in the topmost position of the 9817, leaving out the graphics board

> (the machine ill run without it) and take the top casing off the 9817. Take care to avoid the

> live mains and worse on the PSU board, power it up, and check the HS and VS pins of the 6845

> (the only 40 pin IC on the board)

>

> Most, if not all, cheap composite video converters assume US or European TV rates and are

> not going to lock to this thing. If anybody knows of an interface that will work,

> I'd be interested to know about it too (I have a 9817 with the 98204B card, fortunately

> I do have the right montor for it).

>

> -tony

> ------------------------------

Tony,

thank you for your explanations. As I understand, the unusual low horizontal frequency is the main problem.

I saw that the card has a switch to toggle 50/60Hz vertical frequency (EU/US, original setting was at 60 Hz), but this did not help.

I will see whether I can use my oscilloscope to catch the frequencies as I could not find a technical description of the 98204B.

... and I thought today such a simple problem could be easily solved with modern technology...

Martin