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Cromemco 64KZ-II legend rev B schematics needed

A

Amardeep-AC9MF

Experienced Member
Joined
Jul 22, 2017
Messages
115
Location
Central Indiana
Hello All,

I just purchased the subject memory card and need to replace a missing IC. However this board is older than the legend rev E documented in the copies of the user manual available from the various common archives. If you have those documents or even a picture of an intact rev B I would really appreciate the help

Thanks,
Amardeep
 
Amardeep-AC9MF said:
Hello All,

I just purchased the subject memory card and need to replace a missing IC. However this board is older than the legend rev E documented in the copies of the user manual available from the various common archives. If you have those documents or even a picture of an intact rev B I would really appreciate the help

Thanks,
Amardeep
Click to expand...
You have the 64KZ-II rev B that was recently sold on eBay "for parts" because the seller realized it was missing the socketed digital delay line? If that delay line is the same make/model used in subsequent revisions, it is a "Data Delay Devices Inc" DDU-7-8079. Cromemco did not identify the part number for this delay line in their schematic or manual. Based on the unique functional design shown the schematic for revisions D and E (ie two independent delay lines in the same package) it is possible this part may have been custom-made to Cromemco's specs.
 
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hmb said:
You have the 64KZ-II rev B that was recently sold on eBay "for parts" because the seller realized it was missing the socketed digital delay line? If that delay line is the same make/model used in subsequent revisions, it is a "Data Delay Devices Inc" DDU-7-8079. Cromemco did not identify the part number for this delay line in their schematic or manual. Based on the unique functional design shown the schematic for revisions D and E (ie two independent delay lines in the same package) it is possible this part may have been custom-made to Cromemco's specs.
Click to expand...
Ah, thank you for the hints. Yes this is that specific board. I'll go by the assumption that they kept that delay part the same and try to reproduce its functionality as appears in the later schematic. If that pans out I'll consider it a success. If it doesn't...well that's okay, too.

My system currently has three 64KZ cards and I also found a CCS memory card like I used to have back in my original system in the 80s so it has the Cromemco bank switching support and Cromix compatibility. That will get the system to 256K which is fine for its "mission" to be a playground for Cromix.

Longer term it would be fun to create a new memory board to support z80 Cromix, though. It has to use a discrete memory part for each bank to support the simultaneous bank write function used by Cromix. So a single large SRAM won't do the trick.
 
I just noticed the discussion you started regarding this board in the Google Groups Cromemco forum.
You face a significant challenge in getting this board to work. As you pointed out, Cromemco changed the DRAM controller circuitry from the two-chip Motorola design on your Rev B board to a single chip AMD design on the Rev D/E boards. It is highly likely the specs for the delay line device were also changed. If it were me, I would just wait for another 64KZ-II board to come along.
 
hmb said:
I just noticed the discussion you started regarding this board in the Google Groups Cromemco forum.
You face a significant challenge in getting this board to work. As you pointed out, Cromemco changed the DRAM controller circuitry from the two-chip Motorola design on your Rev B board to a single chip AMD design on the Rev D/E boards. It is highly likely the specs for the delay line device were also changed. If it were me, I would just wait for another 64KZ-II board to come along.
Click to expand...
You're quite right and there's no guarantee that if I accidentally end up with exactly the right delay (improbable) that there isn't something else also wrong with the card...and without schematics that's an uphill battle. I think this is going to end up being a show and tell S100 card.
 
I decided to return it since the seller offers returns. Spent a little too much for it to not be usable. Thanks for all the responses, everyone. Very helpful!
 
Ah, that's what that logo represents, the upside-down triangle with a 'D' in each corner. I have a Rev E board here with that delay line at IC19; a Rev D board has a version from Belfuse, a somewhat better known supplier of these chips, labelled 0447-0200-78 date code 8225 (curious, since the presumably newer rev E seems to be dated 8079).

I was going to offer to lend you one of those for testing, but even if there were no other issues and it did work you'd still have to source one of your own; I think you're right to try to return it; I hope he accepts it.

I'll look forward to your new Cromemco board! It'd be nice to have a new single board that supports all 6 users of Z80 Cromix, especially if it could also supply a vertical configuration for Cromix+
 
Amardeep-AC9MF said:
I decided to return it since the seller offers returns. Spent a little too much for it to not be usable. Thanks for all the responses, everyone. Very helpful!
Click to expand...
... and it is now again listed on eBay, with 4 bids already placed from 2 different buyers.
 
hmb said:
... and it is now again listed on eBay, with 4 bids already placed from 2 different buyers.
Click to expand...
Unfortunately their description is lacking and my guess is most people won't realize there isn't documentation for that specific version of the board.
 
It was something I did over 25 years ago, so probably lost any details I had.
My Cromemco collection hasn't made the head of the rebuild queue yet, although I have confirmed none of the CPU cards in any of the three units still work.
If you were interested I could reverse engineer it.
 
No worries. Just curious if it was already in the archive. Today the 4164 chips are cheap and plentiful so you can just use them in place of 4116 chips by cutting the trace to pin 8 and jumpering to pin 9. This can be done socket by socket if only one or two chips are bad or the whole row at once if replacing wholesale.
 
This is because 5V moves from pin 9 to pin 8 and pin 9 becomes A7 input. The cut disconnects 12V and the jumper brings 5V over to pim 8. Pin 9 remains tied high so it only uses one quarter of the device's RAM array.
 
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