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Apocalypse

Hi all,

I've been finally hit by the failure of that custom module. It's used on many Sega boards (X board, Y board, Systems C/C2/18/24/32) to increase palette.

Since I don't have the tools to decap one I simply pulled a good one and studied it on the bench. It's rather simple (mainly latches and resistors to form a DAC). Only thing I'm not 100% sure of are resistors exact values. I set my PSU to +5.00V and measured voltage before and after the final amplification stage transistors then deducted resistors values for the DAC. One thing I've learned is you can get rid of the transistors by using appropriate resistors values. Sega used much higher values inside the on the module, I guess to limit power dissipation since they are film resistors.

I've made a first repro on a piece of breadboard (a bit shitty since its a SDIP device) and will release gerbers and BOMs here as soon as they're ready scroll down for the gerbers.

Cheers.

[EDIT]
Following the discoveries there:

https://www.arcade-projects.com/forums/index.php?threads/sega-315-5242-reproduction.14034/

I've found this repro is suitable only for System C/C2, X board, Y board and System 24.
If you need one for S18 or S32 follow the link above to @caius repro thread.
Or wait for me to reverse the greyscale effect (shouldn't be too difficult, RGB signals are converted to have equal weight resulting in grey being displayed, probably like Rin+Gin+Bin/3 = Rout, Gout, Bout).

BOM:

PartTypeRef.Comment
J1Connector2*32p 0.7" strip pin
U1, U2IC74LS273SOIC20, 300mil
U3IC74LS74SOIC14, 150mil
U4IC74LS125SOIC16, 150mil
C1~4Capacitor100nF ceramic, 0805 footprint0805 footprint
R1, R7, R13Resistor4K, 0805 footprintCan be substituted by a rounded value of 4,7K
R2, R8, R14Resistor2K, 0805 footprintCan be substituted by a rounded value of 2,2K
R3, R6, R9, R12, R16, R18~21Resistor1K, 0805 footprint
R4, R10, R16Resistor500R, 0805 footprintCan be substituted by a rounded value of 470R
R5, R11, R17Resistor250R, 0805 footprintCan be substituted by a rounded value of 220R


Gerbers:

View attachment gerbers_315_5242.zip

Capture.JPG
 
Last edited by a moderator:
A

Apocalypse

I've reproduced the greyscale effect for S18 & S32. I will print few PCBs and if testing goes well I'll update the gerbers.
 
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