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Darksoft

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THIS IS A REPRODUCTION PROJECT MADE BY @caius ALL INFORMATION HAS BEEN POSTED WITH HIS PERMISION. CREDIT AND MERIT GOES TO HIM.

Got some months ago in a trade this pretty mint original R-Type board:
PCB.jpg

Board was faulty, it was stuck on this static screen:
100_8849.jpg

System is made of three boards:

ROM board

ROM_board.jpg


CPU board

CPU_board.jpg


Video Board:

VIDEO_board.jpg

Swapping all the boards with a good set I could figure out that none of mine was properly working.So I started to troubleshoot the ROM board since it’s the most simple.The program ROMs were dumped as good but I found a bad 74LS245 @1A:
74LS245@1A_failed.jpg

This gave me a working ROM board and a good starting point so I moved on to troubleshoot the CPU board.Analyzing the NEC V30 (uPD70116) main CPU revealed the interrupt line was asserted (active high on this CPU), here’s a screenshot from my scope triggered with RESET signal
PIN18_INT_V30.bmp

The interrupt is generated by the uPD71059C;
Interrupt Control Unit, probing it revealed that input pin 3 (READ STROBE) was stuck low :
PIN12_74LS244-RD_UPD71059C.bmp

This comes from output pin 12 of a 74LS244 @IC72 :
100_9789.jpg

I pulled it :
100_9791.jpg

It failed the out-of-circuit testing:
74LS244@IC72_failed.jpg

Finally the board booted but with multiple issues.First noticeable one was a totally missing sound but this was because the analog audio section was modified (by factory) to work in Nintendo cabinets.I simply reverted the mod by installing the missing capacitors @C101, C102 an C108 and removed the jumper wire:
p data-verified=

All the other issues concerned the graphics.Some examples:
issue_1.jpg


Honestly it would take too long to explain in details what I did (and maybe I even lost track of it…) before the board worked fine again :
102_9929.jpg

102_9930.jpg

All I can say is that I had to replace;
in total 15 TTLs (all from Texas Instruments, are we facing another Fujitsu perhaps?)
102_0052.jpg

But I claimed victory too soon , the board went bad again showing jailbars all over the screen:
102_9879.jpg

I quickly pinpointed this further failure in one of the two ‘KNA6034201’ custom tiles generator on video board:
100_9805.jpg

Testing it on a Kung-Fu Master PCB;
(where it’s used for sprites too) gave me confirm it was really bad :
102_9883.jpg

Looking at this PCB I noticed that the other custom ‘KNA6034201’;
was replaced by a little sub-board:
102_9884.jpg

Technically speaking the custom acts like a big shift register, it can take up to 24 bit of data from tiles or sprites ROMs, here’s snippet from R-Type schematics;:
tiles_generation_1.jpg


As you can see in the sub-board picture above the custom functions have been reproduced using six 74LS166 with common shift load and clock signals.So I wondered myself : why not reproduce it in a more modern way?I fired up my CAD and drawn schematics :
KNA6034201.png

Routed them to a PCB layout :
KNA6034201_PCB__.png



I sent files to manufacturer and after some time I got the bare PCBs:
101_9900.jpg

Here is the final result compared to orginal custom:
101E9910.jpg

Luckily I made no design mistake and testing was 100% successful.Another board repaired and another custom IC delivered to eternity!
 
Nice one @caius! Hope I won't ever need this fix log on my board..
 
Last edited:
I have to get a couple of these as spares, my R-type board suffered the same failure on that IC, thankfully a friend had a parts board and was able to replace it and get my board working.
 
I have to get a couple of these as spares, my R-type board suffered the same failure on that IC, thankfully a friend had a parts board and was able to replace it and get my board working.
I have availabilty of assembled units.You can contact me in PM.Thanks.
 
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