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New Digtal Group Toys

falter

falter

Veteran Member
Joined
Jan 22, 2011
Messages
6,573
Location
Vancouver, BC
Thanks to Marty for sending me all this great stuff! I'm going to dive right in and try to get as much of it as I can working. Having a working DG system already should be a big help.

So my first target is that 32char tv/cassette card. I plugged it in place of the 64 (and switched to the 8080 board) but no picture -- and I'm wondering, would the wiring to the video card slot be different for the 32? Not sure where to begin here. Much reading to do.
 
Made a useful discovery -- I took my semi-flaky 8080 board and swapped the EROM in from the three Marty provided -- now it works more or less perfectly.. loads up the 8080 op sys tape no problem, fires up correctly each time. The only thing not correct about it is the video being garbled but that's because I'm still on my 64char card until I get some idea of what's not happening with the 32 char board.
 
Hi All;

Brad, ENJOY !! Remember, that for the most part, suspect that ALL of the Ic's are not good in all of the Boards, Except for the I/O Board..
Also, Remember that Two of those Eproms were Blanks..
And Yes, the Plug in wiring for the 32 Character and the 64 Character was the same, So they could be swapped Out at time one was needed over the other..
I would USE Your Z-80 Card to Try and Fix these other Cards..
Since I no longer Had a working System, fixing them (easily) was out of the Question for me, since I couldn't be sure that anything including the MotherBoard was any good..

THANK YOU Marty
 
Thanks Marty. Reading the docs for the 32 char card.. they say if no picture is present to first check the crystal. So we'll go there. I'm not sure what to make of all the ICs that are on their backs and wired in. A mod of some kind? I wonder if I should try to take it back to the stock spec in the manual and start there. I figure if the I/O card and 8080 card are good and I get the 32char tv board going I should have a second working system. Can't see what would go bad on the motherboard. I'm also wondering if the motherboard might already be wired for the phideck? Haven't pulled it out of the foam board to look yet. Exciting stuff!

And I really appreciate all the extras. I'll get the shipping charge out to you for sure before the week is out.
 
Well, we're getting somewhere with the 32 char card. I did my crystal tap trick, and went from zero to flashes onscreen. But still nothing resembling a character. I checked the char gen ROM in another TV board and it was fine, so I know it's not that. Still kind of wonder about the crystal. I reseated all the chips (some had come a bit loose in transit). Now I consistently get this screen:

20160714_200749.jpg

And it *is* a screen. If I pull both the 7400s on the far right, that nice light grey box disappears. If I put one in, the box is well defined top and bottom but extends beyond the screen boundary, and vice versa with the vertical if I swap out that one and swap in the other. So it's doing something -- but somehow I think the char gen isn't being engaged. More reading.
 
Hi All;

Brad, "" I'm not sure what to make of all the ICs that are on their backs and wired in. A mod of some kind? ""

Sort of, It's the circuit for writing to the cassette used in a 64 Character Card, which is a better circuit, than what was origionally there..

One way to check many of the IC's in the 32 character card is to pull out an Ic from the 32 character card, find that same IC in the 64 character car.. Pull out that IC from the 64 character card replace it with the unknown IC.. Put the 64 character card in Your Z-80 machine, see what kind of picture it produces..
If it is good them mark it as good and put back what You pulled origionally from the 64 character card and go on to the next IC.. All of the IC's in the 32 Character Card could be checked with Your 64 character Card and Your Z-80 CPU for generating some text..

Also, I just had a thought Is the Transistor in the 32 character Card ?? With it gone there would be NO picture at all..

""Can't see what would go bad on the motherboard. I'm also wondering if the motherboard might already be wired for the phideck? ""
I had a MotherBoard once that Looked fine but, it would not work.. Looks can be deceiving, All wires need to be Ohmed out and cross ohmed out..
Yes it has the Phideck wiring on it..

THANK YOU Marty
 
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I've swapped all the 74193s, 7430, 74157.. no dice thus far. What's this transistor you're referring to?
 
I found the transistor (T1).. and it was in. If I remove it, that faint square box in my pic vanishes.
 
Hi All;

Brad, Good You found the Transistor..
Also, note, that there are some Power traces going up and down on Both the 64 Character and the 32 Character boards, these Lines divide the board in two..
On the Right side of the Lines is the Cassette Circuitry and on the Left side of the Lines is the Video Circuitry..
Also, note the Problems You had Video wise on Your current 64 Character Board with the 2102's and their effect on the Picture produced..
Also, note that the 32 Character Board has only One row of 2102's where as the 64 Character Board has two rows of 2102's..

THANK YOU Marty
 
Yes I swapped out the video RAM with known good. So that shouldnt be the issue. Ive almost checked all the ICs so I'm beginning to think crystal.. cant find a replacement online though.
 
Hi All;

Brad, Here are a couple of things to try..
First as many of us have Said Before, You NEED a Scope, Even a Lower Frequency one would work in a pinch..

Two, take out the Crystal from one of the 64 Character Cards, and put it in the 32 Character Board, I know it is double the Frequency, But, it should show something on the screen, even at that higher frequency, just for a test of Your Theory of what is Wrong..
Second, If You have a BreadBoard hook up a circuit with like a 7474 or something like that and the crystal tied to its input, that should half the frequency and wire that to the 32 Character card..
If You can't find one with the right frequency, I think I have one, I will look and see for sure if You need it.. And Send it to You..

THANK YOU Marty
 
Heh. The Flintstone approach worked.

Suspecting the crystal, which seems to be a theme throughout my adventures with old Digital Group stuff, I bent it out a bit, and then gave it a good couple whacks with my screwdriver. Sure enough:

20160715_091740.jpg

So then I tried loading a tape, which I know works with the 64 char board I have. But no dice.. the 1s appear slowly and then just stop. I think the cassette side of this thing is going to be much harder to diagnose.
 
Hi All;

Brad, Congratulations !!!

I wouldn't recommend You Crystal Fixing approach, But, Yeah but it works !!

Actually, You may be alot closer than You think.. First Read up on Aligning up the Cassette Reading Circuitry, Its the same for Both the 64 and 32 Character Cards.. On the Top of the 32 Character Card is a Variable Resistor, It looks like it needs a slight Tweaking, from the last time it was used..
It is Real Easy to Align..

THANK YOU Marty
 
Ah yes.. I was playing with that earlier thinking it had something to do with video. Thanks Marty.

My 8080 board is still flaking out unfortunately. But at least I have spares now to try and get it going. The IO board also has some issues I have to sort.

BTW.. for keyboard.. did they always use an edge connector? Even on the really homebrew ones? Once I get this all sorted I want to transfer and create a separate 8080 system.. but it'll need a keyboard. I wonder if it'd be possible to recreate the edge connector.
 
Hi All;

Brad, "" BTW.. for keyboard.. did they always use an edge connector? Even on the really homebrew ones? Once I get this all sorted I want to transfer and create a separate 8080 system.. but it'll need a keyboard. I wonder if it'd be possible to recreate the edge connector. ""

You can Use any Type of Connector that You want to use, as long as it has enough fingers for all the Wires that are needed to attach to the KeyBoard that You Plan on using..

"" Ah yes.. I was playing with that earlier thinking it had something to do with video. Thanks Marty. ""
You Definitely put it out of Wack, that way..

"" My 8080 board is still flaking out unfortunately. But at least I have spares now to try and get it going. ""
Hopefully with what You got from me, there should be enough spare Ic's to help You find the Problem..

"" The IO board also has some issues I have to sort. ""
I thought that, that was the Only Good Board of the Bunch.. Goes to show what I know..

I keep asking and You so far have Ignored my Question.. Did You find the Little Black Box with Ic's in it ??

THANK YOU Marty
 
Oh sorry.. missed that question. I did find the black box at the bottom of the other box! Many thanks! 2102s and spare cpu are always useful!
 
falter said:
BTW.. for keyboard.. did they always use an edge connector? Even on the really homebrew ones? Once I get this all sorted I want to transfer and create a separate 8080 system.. but it'll need a keyboard. I wonder if it'd be possible to recreate the edge connector.
Click to expand...

A little 22/44 paddle board would be easy to lay out, if you're interested. I was still on the fence about using the edge connectors for I/O or using one of the D-SUB knockouts, since my Digital Group system doesn't have a keyboard.
 
Yeah.. I'm interested. Wish I was more skilled. Working on it. :) I have three keyboards that would at least be plausible for a DG system of that era -- 2 are Decision Data 8010 punch keyboards, and one is a Univac punch keyboard from 1970. Obviously would need a major rewiring and some kind of encoder built. I'm not sure exactly if I understand how ASCII works -- ie if I were to take one of Lancaster's 7 bit ASCII encoders.. if the output from that is just a matter of wiring correctly to the DG system, or if the 'format' will still be something the DG isn't expecting.
 
Yeah I think this crystal on the TV board is giving me grief. The board will go completely out.. I tap it, it comes back. I got it dialed in well enough to actually boot the 8080 op sys tape properly, once, but without any prompting as I was about to take a picture it jumped into one of the keyboard functions and then went completely nuts. I don't know what it is with crystals but I find it really difficult to find any of the ones I need new. I just did a cursory look and 5.99mhz seems to be a bit of an oddball, again.
 
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