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MDA card with RCA jack question

agentb

agentb

Experienced Member
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Apr 22, 2021
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Philly, USA
Quick question, what is this RCA jack on this MDA card? Is it composite video? (As I don’t have any monitor to hook the 9-pin to.)

Also, in attempting to test a 5150 board, is connecting +5V and GND sufficient or do I also need to put +5V on that “power good” line - i most certainly do not have the proper XT/AT power supply to test the 5150 board.

Thanks for any info.D27C5892-0A8C-44FE-A5AE-DC7C63E109E6.jpeg
 
Re: the RCA jack, a better view of the rest of the card might give clues. It looks like a late high-integration card with that big flat-pack on it, so there's a decent chance it's actually a dual-mode card that supports both MDA and CGA modes.
 
Eudimorphodon said:
Re: the RCA jack, a better view of the rest of the card might give clues. It looks like a late high-integration card with that big flat-pack on it, so there's a decent chance it's actually a dual-mode card that supports both MDA and CGA modes.
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Ahh interesting, OK, I'll supply a pic of the card -- yes, I believe the date code on the card was significantly later.
 
agentb said:
Looks like my problem with the POWER GOOD line is that you have to briefly take it low, before taking it to high.
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Nice, looks like tapping into the POWER_GOOD line from the ATX power supply solves the problem of turning on. Now if only I can find a way to get video...
 
So... that's (probably) not an MDA card at all. Here's a thread on Vogons.

This card has 16K on it (too much for MDA, too little for Hercules, just right for CGA), and, more crucially, it doesn't have the 16.25Mhz crystal that's required for the dot clock of an MDA monitor. There's a post in that thread that suggests that the flat pack chip on there supports both CGA and Hercules if it's fitted with the necessary external components for the mode chosen, but the amount of RAM and lack of crystal means this is a CGA-only version of the board.

And nobody seems to know what all those jumpers do other than the printer one, so you probably don't want to touch them. Some of them *may* configure whether or not the RCA port has a colorburst signal available or not. (It was not uncommon for late CGA implementations to only support mono on the RCA jack, because that makes for a cleaner display on a cheap mono monitor.)
 
Thanks for the info and link -- I'll check that out. I tried setting the 5150 DIPs to CGA and then started getting some output on the RCA. My composite monitor doesn't like it so not sure what exactly is being output. But good news is that the motherboard seems to at least be working.
 
Eudimorphodon said:
And nobody seems to know what all those jumpers do other than the printer one, so you probably don't want to touch them.
Click to expand...
I have another one of these CGA cards, but without the RCA jack. Jumpers match on both cards, along with the same settings of a number of the cards on the vogons link. Would be nice to know what they do. Ahh well, I may try another config of the jumpers I saw on the vogons link.
 
Just tried the inverse of the jumpers -- I changed UP-DOWN-UP-UP to DOWN-UP-DOWN-DOWN. And BAM, composite output!
A4F13789-75FE-4057-ADD7-C88DA3B1F44A.jpeg
 
agentb said:
I have another one of these CGA cards, but without the RCA jack. Jumpers match on both cards, along with the same settings of a number of the cards on the vogons link. Would be nice to know what they do. Ahh well, I may try another config of the jumpers I saw on the vogons link.
Click to expand...

The one without the jack doesn't have 64K instead of 16K and a crystal in that silvery spot, does it? It's very possible they sold Hercules cards with this identical PCB.
 
Eudimorphodon said:
The one without the jack doesn't have 64K instead of 16K and a crystal in that silvery spot, does it? It's very possible they sold Hercules cards with this identical PCB.
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Nah, it's nearly the same -- with the 16K RAM and no crystal. Just seems to lack the Composite output. But it does have a 2-pin header labeled 'CN2' which appears to be the composite output.
 
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I think I'm blocked at this point -- lacking an XT keyboard. But really didn't have any plans I was trying to achieve with this other than seeing if I could get it to POST hotwiring with a Sun Ultra ATX power supply...
 
For what it's worth, I recently did an article on a bunch of these CGA cards with the VDL chip. I still haven't managed to get composite out from the 2-pin header, so if anyone has discovered how I'd be interested!
 
DOSDays said:
For what it's worth, I recently did an article on a bunch of these CGA cards with the VDL chip. I still haven't managed to get composite out from the 2-pin header, so if anyone has discovered how I'd be interested!
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Thanks for the writeup on the CGA cards. After some review of your article, and my cards, and this FIDA MIX link, I believe these are the jumper settings for my VDL cards:
1 - Positive VSYNC (hardwired to ON/positive on one of cards)
2 - Positive HSYNC (hardwired to ON/positive on one of cards)
3/4/5 - settings for RGB/TTL/Composite

Off-On-Off for 3/4/5 got me Composite mono working. I just tried changing to Off-Off-On and sure enough that gave me Composite color. So looks to be matching the FIDA MIX jumper settings -- at least for the 1-5 settings.

Looking at your "Expert" card, I see you have the 1 and 2 hardwired on also. So 3-4-5 are probably your jumpers for getting that composite header working. They are set to On-Off-On now for RGB. Would need to be set to Off-On-Off or Off-Off-On to get you composite on that header. That's my guess!
 
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