DG-32D memory board?

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Mike Ladwig

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Jul 6, 2022, 11:04:04 AMJul 6
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Hi!

I'm having problems with my DG-32D memory board. All of the sudden, my card's bank B isn't working at all, leaving me with only 16k of memory.

In looking back through the archives, I see that people have these cards but no manuals. Asking to see if since those questions anyone turned up a manual and/or schematic for it.

If not, does anyone know of other cards also based on the Motorola mc3242ap address multiplexor? Probably not too many ways to use it. 

Thanks,
mike.


norberto.collado koyado.com

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Jul 6, 2022, 5:49:43 PMJul 6
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If you want to have a better reliable system, it will be better to have one of the newer boards.

 

Norberto

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Glenn Roberts

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Jul 6, 2022, 5:54:38 PMJul 6
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The older DRAM boards can be quite problematic…

Gery Kissel

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Jul 6, 2022, 8:05:35 PMJul 6
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My DG-64D board was the motivation for all the restoration work I did and finished around 2 years ago.
A tantalum cap let loose on the board and I decided it was time to do what I could to make the entire system last as long as possible (the early part of the pandemic helped also).
I put some feelers out to get a schematic/docs for the board as it is the only board I have missing all the info.  I made a contact after some internet searches (not in this group) but that never panned out.

Fortunately my board was not damaged when the cap went off and all the restoration work will hopefully last another 40 years.

During the restoration process I found this group and a lot of help.

I eventually decided to build one of Norberto's V4 boards and put all the original / functional boards in delectate storage.

If you do manage to find any docs, please mention in the group.  I would like to have a copy for my records.

Regards,
Gery

Dave McGuire

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Jul 6, 2022, 8:18:21 PMJul 6
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On 7/6/22 20:05, Gery Kissel wrote:
> My DG-64D board was the motivation for all the restoration work I did
> and finished around 2 years ago.
> A tantalum cap let loose on the board and I decided it was time to do
> what I could to make the entire system last as long as possible (the
> early part of the pandemic helped also).
> I put some feelers out to get a schematic/docs for the board as it is
> the only board I have missing all the info.  I made a contact after some
> internet searches (not in this group) but that never panned out.
>
> Fortunately my board was not damaged when the cap went off and all the
> restoration work will hopefully last another 40 years.
>
> During the restoration process I found this group and a lot of help.
>
> I eventually decided to build one of Norberto's V4 boards and put all
> the original / functional boards in delectate storage.
>
> If you do manage to find any docs, please mention in the group.  I would
> like to have a copy for my records.

I had been searching for DG-64D documentation for some time also, and
someone here provided them. I'm sorry but I don't remember who it was.
I just sent you the two PDFs off-list.

-Dave

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Dave McGuire, AK4HZ
New Kensington, PA

Benjamin Hansen

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Jul 6, 2022, 10:19:49 PMJul 6
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I've just inherited all the H-8 stuff I help build growing up.  I probably have the manual and schematic you are looking for.  I will check my boxes tonight and get back to you.

Ben Hansen

Mike Ladwig

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Jul 7, 2022, 4:45:29 PMJul 7
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Thanks everyone. While the modern memory boards would be the "best" solution, my interest in these old computers is keeping them as original as possible unless there's no other option. I haven't had much difficulty if NOS RAM chips can be found, which is most of the time.

I did find a few S-100 bus memory cards that used the 3242 in address handling (Central Data 64, Zs Systems 64) so am looking at those schematics to try and figure out how it helps manage ram banks. Does the DG-64D use the 3242 as well? If so, it's probably very close to the DG-32D so I'd appreciate a pointer to the schematic if possible.

Thanks,
mike.

Dave McGuire

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Jul 7, 2022, 5:05:46 PMJul 7
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On 7/7/22 16:45, Mike Ladwig wrote:
> I did find a few S-100 bus memory cards that used the 3242 in address
> handling (Central Data 64, Zs Systems 64) so am looking at those
> schematics to try and figure out how it helps manage ram banks. Does the
> DG-64D use the 3242 as well? If so, it's probably very close to the
> DG-32D so I'd appreciate a pointer to the schematic if possible.

It does use a 3242. I've sent you the schematic off-list.

Mike Ladwig

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Jul 8, 2022, 9:23:19 PMJul 8
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IMG_4202.jpeg

Fixed! Now seeing all 32k of DG-32 RAM. Better yet, now the new-to-me H17 (thanks Glenn!) is happily booting into HDOS!

The DG-64 schematic (thanks Dave!) was very helpful in figuring out the DG bank select approach, but after a couple of hours tracing signals I realized addresses above 3FFF weren't consistently getting to the card. Moved it to another motherboard position and it worked perfectly. Cleaned the original connector with DeoxIT, put the card back, and it worked fine there too. 

I think my problem is that I have an early H8 without the later gold pin bus connectors. I understand owners of the early systems often upgraded to the later connectors. Has anyone here done it? How painful was the process, and did it improve things? Do you need to do both the motherboard and the cards?

Thanks!

glenn.f...@gmail.com

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Jul 8, 2022, 10:34:41 PMJul 8
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Great progress Mike!

 

Yes I’ve replaced the tinned connector pins on a number of backplanes.  I used these parts from Phoenix Enterprises:

https://www.peconnectors.com/index.php?p=catalog&mode=search&search_str=hws3002

 

but obviously headers are available from many sources.  Just make sure you’ve got the .318” height

 

the main difficulty is de-soldering the old connectors.  If you’ve got the right de-soldering tools this goes pretty well.  the other trick is when installing the new headers it is best to have a female connector of some sort inserted into the headers.  This helps keep the pins straight and at a right angle to the board.  I have a little jig I use for this purpose.  You could probably just use an H8 board of some sort.

 

If you do this repair let us know  how it goes or if you run into any problems…  I do recommend it as the old tinned connectors will give you headaches (as you’ve discovered!).

 

I did not find it necessary to replace any of the female board edge connectors…

 

  • Glenn

 

 

 

 

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Mike Ladwig
Sent: Friday, July 08, 2022 9:23 PM
To: SEBHC <se...@googlegroups.com>
Subject: Re: [sebhc] DG-32D memory board?

 

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image001.jpg

Peter Higgins

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Jul 8, 2022, 10:39:02 PMJul 8
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I replaced all the backplane connectors with gold-plated ones on one of my older H8s a couple of months ago. I have a powered-suction desoldering tool (the Hakko FR-301) which made the process fast and painless. Without such a tool the recommended (and far more painful) method is to pull each pin out individually from the front of the board as you heat the solder side of the pin on the back followed by a cleanup of each hole with flux and solder wick. See this comprehensive discussion on the topic:

I too used DeoxIT with the older tin-plated connectors and for a while it did improve reliability, however inevitably the glitches came back. The change to gold-plated connectors was a significant improvement. I noticed right away how smoothly each card could be plugged in. Prior to the swap my H8 would frequently glitch and stop running - that no longer happens, and I no longer need to "jiggle" the boards to keep things running.

I have not tried swapping out the sockets with tin-plated contacts found on some of the oldest cards (like the 8K RAM boards and the original 8080 CPU board) since I no longer use them. Replacing these sockets without a desoldering tool would likely be a painful process.

norberto.collado koyado.com

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Jul 9, 2022, 2:32:39 AMJul 9
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Great work! I need to get for myself a Hakko FR-301, perhaps for X-MAS. Once you update to gold pins, the reliability of the system improves by a 100%. The H8 will work as it was designed for. I never got my original tin plated backplane to work reliable. I was never able to do anything as the system will hang at random. Once I updated to gold plated pins, the system never., never failed again.

 

Norberto

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Peter Higgins
Sent: Friday, July 8, 2022 7:39 PM
To: SEBHC <se...@googlegroups.com>
Subject: Re: [sebhc] DG-32D memory board?

 

I replaced all the backplane connectors with gold-plated ones on one of my older H8s a couple of months ago. I have a powered-suction desoldering tool (the Hakko FR-301) which made the process fast and painless. Without such a tool the recommended (and far more painful) method is to pull each pin out individually from the front of the board as you heat the solder side of the pin on the back followed by a cleanup of each hole with flux and solder wick. See this comprehensive discussion on the topic:

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norberto.collado koyado.com

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Jul 9, 2022, 2:43:15 AMJul 9
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As a note, you can easily update the original H8 backplane with gold pins, as each hole is not plated thru. Solder is just on side 2 on each pad. The drawback is that when inserting a board, the pads on side 2 can be easily broken. The new golden pins will make it easier to insert with less force.

 

On the New backplane the holes are plated thru, so they cannot be removed once soldered in. Solder will be on side 1 and side2 of the board.

 

Norberto

Steven Hirsch

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Jul 9, 2022, 9:21:59 AMJul 9
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On 7/9/22 02:32, norberto.collado koyado.com wrote:

> Great work! I need to get for myself a Hakko FR-301, perhaps for X-MAS.

It's an amazing tool, Norberto. I've probably removed in excess of 150 DIP
ICs and sockets from PCBs of all types and have yet to tear or lift a trace.
Having the vacuum pump located immediately adjacent to the barrel makes a huge
difference. The long flexible hoses used on many tools act as a series
inductor and "blunt" the surge enough to reduce their effectiveness at
clearing solder.

Dave McGuire

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Jul 9, 2022, 9:27:56 AMJul 9
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Another vote here for the FR-301. I use mine regularly. The only
pads I've lifted with it have been on Data General boards from the early
1970, whose pads seem to come pre-lifted from the factory. ;)

It's one of the best thought-out tools I've ever seen. Run, do not
walk, to Amazon's website and order one.
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