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I'm in a trouble. Can someone help me?

I have a very big machine where I had mounted an IBM 5151 monitor by VGA. The VGA cable was connected to the card below (see attachment), by 4 wires.

Now the monitor is broken and I'm in trouble. Can anyone help me?

I want to connect a single RCA wire (the yellow) directly in the card in place of the 4 wires of the VGA (wires grey, green, pink, white, to be clear.) The RCA cable has 2 wires, one yellow and one black.

What can I do?

Please it's really important.

enter image description here

JRE
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Marc Aurel
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  • Otherwise... I have a 9 pin vga output. I can use a transformer 9-pin to 15 and connect a normal LCD? The ibm 5151 has a low resolution and 50hrz of requence, any problem about?? – Marc Aurel Nov 12 '20 at 11:00
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    No the output is not VGA. It is MDA. It is not compatible with VGA in any way. I am having trouble deciding if this is a repair question without understanding the device being repaired, what to buy question, or how to use devices question. – Justme Nov 12 '20 at 11:07
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    the circuit looks suspiciously like an MDA to compositie converter. find someone who knows the device they will tell you which pin has compositie video on it. – Jasen Слава Україні Nov 12 '20 at 11:09
  • The configuration in photo works... i want to resolve it in any way possibile. I can't go to search for a IBM 5151... That's the big problem – Marc Aurel Nov 12 '20 at 11:13
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    @Jasen MDA being 18.4kHz 50Hz would not be compatible with composite 15.6kHz 50Hz. – Justme Nov 12 '20 at 11:15
  • Any MDA monitor will do. Or MDA to whatever you like converter box and modern monitor. It does not have to be IBM 5151. – Justme Nov 12 '20 at 11:16
  • I'm not sure what this "two mini cables" is; normally composite video is only one RCA plug (containing signal and ground). Is this maybe S-Video? But as Justme says, without a service manual for the device in question (or even any labels!) we're just guessing. – pjc50 Nov 12 '20 at 11:16
  • If the those colours are right they are running the display at half brightness. pin 4 is ground abs pin pin 5, 3, or 2 is video. – Jasen Слава Україні Nov 12 '20 at 11:17
  • The chip on the circuit board is a 74HCT14N. It's a Schmitt trigger (x6) which I assume is for the six inputs to the circuit board. It operates at TTL level (0 to 5 V), not VGA level (0 to 0.7 V) – tim Nov 12 '20 at 11:17
  • old schools CRT monitors could have their sync rate adjusted easily, LCD monitors may or may not be able to sync – Jasen Слава Україні Nov 12 '20 at 11:19
  • The board (that includes 74HCT14N) is attached with the cable in the photo. This is the vga cable connected with the IBM monitor, modified from 9 pins to 6 pins (3 color pins removed). – Marc Aurel Nov 12 '20 at 11:22
  • Do you have a wiring diagram for the circuit board? Can you take the PCB out and trace the signals? If that cable really is a VGA cable (and not [MDA for IBM 5151](https://en.wikipedia.org/wiki/IBM_5151)), are the wires HSYNC, VSYNC, GREEN and GROUND? – tim Nov 12 '20 at 11:34
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    Here's the [Original Monochrome Display and Parallel Printer Adapter found on the IBM PC (IBM 5150)](https://en.wikipedia.org/wiki/IBM_Monochrome_Display_Adapter#/media/File:IBM_PC_Original_Monochrome_Display_and_Parallel_Printer_Adapter.jpg). In the top-right corner you can see the 9-pin MDA output. It's not a 15-pin VGA output. – tim Nov 12 '20 at 11:47
  • From my 5151 outputs a vga cable (without 3 pins). I'm looking for the machine circuit board – Marc Aurel Nov 12 '20 at 11:54
  • This is the output of actually (broken) 5151 => https://ibb.co/g4tMHYM This be connected here => https://ibb.co/jkmymK0 By the cable in the photo ("This cable is 9 pin-vga") – Marc Aurel Nov 12 '20 at 11:57
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    That's the MDA connector and here are the [MDA pin-outs](https://en.wikipedia.org/wiki/IBM_Monochrome_Display_Adapter#Specifications). – tim Nov 12 '20 at 12:02
  • Perfect dude. What can i do? – Marc Aurel Nov 12 '20 at 12:14
  • Make sure that it really is only the monitor that is broken. It could be the MDA card as well or instead of. Then [follow the advice of @pjc50](https://electronics.stackexchange.com/a/531946/248838). – tim Nov 12 '20 at 12:31
  • Only the monitor is broken. Circuit board => https://ibb.co/THhXwgC – Marc Aurel Nov 12 '20 at 12:56

1 Answers1

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There are a number of problems you have here:

  • VGA is 15 pins, not 9

  • RCA is composite video, not VGA

  • IBM 5151 is neither of those, it's an old standard "MDA" (monochrome display adapter).

It appears from the internet that MDA isn't a subset of VGA - you can't convert from one to the other by simple wiring.

Your options are:

  • find an old IBM 5151 that is still working, or repair the broken one

  • buy an MDA to VGA converter and wire it appropriately. "Industrial" versions of these can be found on Aliexpress and other vendors; it seems that this is a common problem of industrial equipment with obsolete monitors.

  • trace the video signals further back from that board and find a more useful one (unlikely, since this looks very old .. how old is it? 80s?)

pjc50
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  • I want to remove the VGA and put into the 1,3,4,6 slots (see the image) only 2 cables (the cables from the rca yellow). I had tried it and for seconds it works, but after removed it the connection was losted... So i don't know where put the positive and the negative of rca (what slots from 1,3,4 or 6)... – Marc Aurel Nov 12 '20 at 10:52
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    @MarcAurel This answer clearly explains that there is no "VGA" here and that an MDA signal is not compatible with composite video, which makes your commenting pretending otherwise quite disappointing. Until you recognize the reality of the situation there's really no way anyone can help you, that said the question isn't on topic here anyway. – Chris Stratton Nov 12 '20 at 16:13