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It’s unboxing time! More junk I don’t need and probably paid way too much for!
Under the bubble wrap are a bunch of packets of ... bubble wrap!
Inside the bubble wrap is a card for an Apple II, a Videx 80 column card. I think this is the 4th one of these I own now. It included the soft switch board which is like a mini KVM so you can switch between the Apple’s composite output and the 80 column composite from this card.
And the other thing in this bundle is an Amdek DVM “Digital Video Multiplexer”. I would be pretty surprised if very many people have heard of this much less ever seen one. What is it? It’s a CGA card for the Apple II+! Finally something to put in my empty slot.
I’m very curious to try it out. As you may or may not know, the Apple II has 15-16 colors (technically both grays are the same) and CGA can do 16. I believe this card is limited to 8 though, no intensity bit. And the CGA colors are very different from the 15 the Apple II can do.
Using a CGA signal on an Apple II seems like a strange choice to me. It makes more sense to me to use something closer to Apple II colors, like EGA. Or better, analog. Amdek madee their own CGA monitor (which I don’t own but may get), perhaps this card was to sell more monitors?
The reason the 80 column card was included with this Amdek DVM card is because the DVM card is supposed to have an additional monochrome input which you plug the 80 column card into. Supposedly the 80 column card has to be modified to do that and maybe this one already has that.
I have yet to find the user manual for this card, I’ve been searching for anything I can find while I was waiting for it to arrive. About all I’ve found is a Creative Computing article about it. https://www.atarimagazines.com/creative/v9n1/30_High_quality_hires_Amse.php">https://www.atarimagazines.com/creative/...
Here’s an ad for the Amdek DVM and CGA monitor. You might notice the monitor looks identical to the Color-I composite monitor (which often features prominently in pictures of my Apple II+).
Pictures of the Amdek DVM and Videx 80 column board. The Videx board *has* been modded and I’m glad it was bundled since I have found ZERO documentation for the Amdek DVM.
The Amdek DVM also has two little satellite PCBs that have to be installed into the Apple II motherboard. You remove the chips from the motherboard, put these boards in, and put the chips into the boards. Not sure where they go but having chips still in them should help.
It looks like the PCB with 4 chips goes at D11-14 since that& #39;s the spot with four 74LS161 chps.
The 2 chip board must go at B6&7 since that& #39;s the only place I can find with two 74LS257 chips next to each other. But that& #39;s way up under the keyboard which means I& #39;m going to have to take the whole computer apart.
Apple II+ disassembled. Mostly. This is such a pain because of the RF shield at the back which slips under the motherboard.
ICs at D11-14 and B6-7 carefully removed and put in a safe place.
Amdek PCBs installed. Now to put the II+ back together.
I suppose I should probably test the II+ to make sure it still works with just these new PCBs installed.
And it doesn’t work anymore. 
https://abs.twimg.com/emoji/v2/... draggable="false" alt="😔" title="Nachdenkliches Gesicht" aria-label="Emoji: Nachdenkliches Gesicht"> Power light turns on but no beep and nothing on the monitor. No beep would have to be the 74ls257s at B6-7 because the other chips are just for the display.
I was able to fish the PCB out from under the keyboard without dismantling the II+ again. Hopefully I can put it back under there too. Is the 257 a chip I can test in the TL866? Guess I’ll find out.
The TL866 is able to test them and they pass! Got them re-installed under the keyboard. Not easy. And I get a beep now! But still no video. That’s gotta be the four 161s on the other board. Pulling and testing...
The 161s pass too. Still no video. Must be a problem with getting the PCB pushed all the way in. It’s 64 machine pins trying to shove into IC sockets and they don’t want to go in. Plus the motherboard keeps bending a bit which is probably not so good.
If I press on the PCB while the computer is powered up I get a garbled display so that’s definitely where the problem lies.
Folded a popsicle stick in half and shoved it under the motherboard. Was able to press down VERY hard without the motherboard bending. Feels like I got the pins all seated. Maybe.
Hurray! My II+ works again! Now to get the Amdek DVM and 80 column cards installed.
DVM and 80 column card installed. And the II+ is still booting up! Now to try the CGA monitor. It probably won’t work because I’m connecting IBM to Apple.
And ........................... it doesn’t work. Argh. But it’s not a solid white screen, there’s some black borders so it must be receiving a video signal.
80 column mode works! And wow is it sharp! Crisp readable text.
What about graphics? Hmm, lo-res seems to work. But it’s all white at the bottom where the 40 column text should be.
Let’s try a lo-res color chart. It works! Only 8 colors on the CGA monitor and they are mapped a little strange, but that was to be expected. But where’s my 40 column text?
What about hi-res? The color mapping on hi-res isn’t too bad.
Weird little black dot in the last white column though. Maybe a bad RAM chip on the DVM card? Does it even have RAM chips?
Put my SASI card back in so I can boot the hard drive and run Kermit. That 80 column text is beautiful! So much more legible! IBM CGA display on the left, Amdek color composite on the right.
If you’re wondering how I took those 80 column pictures of a CRT without any glare and such deep blacks, I made a special shroud just for that purpose a long time ago.
Gonna have to figure out what’s wrong with the DVM card and why 40 column text doesn’t work. I really like how readable the 80 column text is. I was worried that the HGR colors were going to be awful but they look fine. The GR colors aren’t so good but I don’t do GR that much.
This is definitely going to be my favorite BBS dialup machine as soon as I get the 40 column mode fixed. That text is so easy to read compared to composite.
And of course gotta test LodeRunner on the Amdek DVM and CGA monitor!
No RAM chips on the DVM card, it& #39;s all 74xx logic. I& #39;ll have to pull them one at a time and test as many as I can in my TL866. Too bad there& #39;s no schematics.
Tested all the chips supported by the TL866 and they all test good. (Ignore the wrong color in the corner, I grabbed the wrong pen.)
If you were paying really close attention to the photos of the cards you might have seen this one wire with a connector hanging off it. No idea it is supposed to connect to since there is no manual for the Amdek DVM card anywhere.
Just for the heck of it I touched that pin to ground and look at that! The white where the text is supposed to be turned black! So that pin must need to connect to something on the Apple II+ motherboard. But where?
Clearly it& #39;s supposed to hook to a pin coming off the text generator circuitry. But I don& #39;t know of any ready to plug into header pin on the motherboard like that. Going to have study the Apple II schematics I guess.
Since the wire is short and comes off the rear connector of the card it must be intended to plug into something at the back of the motherboard. Is it supposed to plug into the composite header?
Yup, it plugs into the composite header! 40-column is working!
This should freak people out. My Apple is using an IBM display!
Supposedly there’s a way to poke some registers on the card to change it into a green screen. But I poked all the bytes in the card’s IO space $C700-$C7FF and nothing happens.
