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Datapoint 2200 / 5500 Ram display logic board schematics drawn up.

jdreesen

Experienced Member
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Jul 5, 2012
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414
Location
Switzerland
Just as a backup : here is the schematic I have drawn up for the "high-speed" Display Logic Board, as uses in later variants of the Datapoint 2200, the 5500, and probably also the 6600.
These have the programmable characterset as described in the 5500 manual and uses the "diddle-scan" character-per-chararcter display.
Note that the backplane wiring diagram in Bitsavers "2200_drawing_package" is for earlier versions of the machine, my 2200 ( actually a 1131) has a considably expanded backplane.

Interesting to see that there is a serious designerror in this PCB : one of the 120 nF decoupling caps is actually connected to a SRAM address line.......
 

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  • RamDisplayLogic.pdf
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And since I am at it, here is the DP2200 main board schematic, drawn up as a hierarchical Kicad schematic. I am tempted to create a new, standalone TTL-cpu from this base.....
 

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  • DP2200_mb.pdf
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Note that this is the mainboard schemtic only : clock generation and IO instruction decoding sits on a separate board, keyboard logic is another board ( and also contains the IO-bus comparators). The DP2200 has modulator & demodulator boards for the cassettes, my DP1100 has a bootrom board instead of the demodulator. This mimicks a serial bitstream from the cassettedecks. The DP5500 has the exact same bootrom board, but only a switch is fitted, the actual bootcode sits in the system ROMS.

Resistor and capacitor values/names are not 100% equal to the MB, IC names should be identical. DP2200 has standard TTL, not LS as in my redrawn schematic . (DP5500 has S-TTL)
 
I will continue this thread with a reverse engineered schematic of the powersupply in my DP1100 / 2200. It is an improved variant of the earlier one , described in the bitsavers docu. It is used in later variants of the DP2200 and DP5500, later variants of the 5500 and 6600 use an entirely different PSU

Note that this design, and its execution, are lethal : You have TTL circuitry without isolation from mains, alsio an optocoupler where both sides are galvanically connected to mains. Also a transformator 110/220 -> 2x15 where the secondary is also connected to mains.......

It is a 2 stage switcher, only the second stage is isolated from mains, but very badly so : the toroid transfomer is sitting on the PCB with life wires running below it : only isolation in my machine was the lacquer on the final stage windings, as the glue which held the toroid inside its casing had failed, allowing the toroid to sit directly on the PCB....

Here 2 pic with component labeling, PSU schematic is picture below :


psu_cmp_1.jpgpsu_cmp_2.jpg



As an aside : here my 2200 is parked in "service position" allowing access to the PCBs. Note the pin of the side holding the unit in a tiltet position. Normally the keyboard blocks access to the PCB's

service_up.jpg
 

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  • DP2200_psu.pdf
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