Board is a bit dusty but very clean nonetheless. Some very specific chips are rusty, probably due to some rodent fluid. Tracks are invisible and located in the core of this 4-layer board making the inner tracks very fragile when pulling a chip out.
![](https://jammarcade.net/images/2024/04/IMG_20210711_143118.jpg)
Game starts when powering the board with full sound and some graphics. The title screen has a white background instead of black as it should be. A similar white background appears during attract mode:
![](https://jammarcade.net/images/2024/04/IMG_20210711_143040-scaled.jpg)
Cross-testing the board with a good one points the fault to the bottom board (graphics board). On this board I started probing the 8 EPROMs filled with the background graphics data. Some pins are quite corroded, so I decided to dump them to check their contents against MAME data:
![](https://jammarcade.net/images/2024/04/IMG_20210711_143129-scaled.jpg)
As a result, EPROMs 10 and 14 are dead. I burnt two replacement EPROMs and that brought the background back:
![](https://jammarcade.net/images/2024/04/IMG_20210711_143223.jpg)
Background is back but the sprites are blinking, they are misplaced and have bad colors. Sprites are generated by the custom chip Mitsubishi M60002-0118P and displayed through twenty 4164 DRAMs. These are known for having a high failure rate. I will focus my investigations in this area:
![](https://jammarcade.net/images/2024/04/IMG_20210711_142933-1-scaled.jpg)
![](https://jammarcade.net/images/2024/04/4164-Pinout-356x360-1.jpg)
Probing the D-OUT pins of these DRAMs (pin 14), 8 DRAMs out of 20 shows an output signal stuck low or even floating when the game has to display sprites:
![](https://jammarcade.net/images/2024/04/IMG_20210711_183919-scaled.jpg)
I pulled these 8 D-RAMs:
![](https://jammarcade.net/images/2024/04/IMG_20210711_183348-scaled.jpg)
All of them were confirmed bad out of circuit.
I fit 8 brand-new replacement DRAMs. Some sprite glitches are still visible – two other DRAMs have just gone bad. I took those out and replaced them. Now the sprites and backgrounds appeared to be rendering properly. However, the sprites motion is still jerky.
![](https://jammarcade.net/images/2024/04/IMG_20210711_213902.jpg)
Rygar shares the same hardware as Silkworm and has schematics available. In the schematics, we can see that two 6116 SRAMs handles foreground and background graphics and a third one is dedicated to sprite positioning (SP/POSITION.RAM as per the schematics). This is the area I will inspect.
![](https://jammarcade.net/images/2024/04/silk_schm.png)
Inspection of the SRAM chip at location 6L doesn’t show anything abnormal. While probing around the area, I came across a signal stuck high on a 74LS193 binary counter (BORROW output) located at 7K. I double-checked it with my logic comparator:
![](https://jammarcade.net/images/2024/04/IMG_20210712_212123-scaled.jpg)
Red light indicated a bad output – I pulled the suspect:
![](https://jammarcade.net/images/2024/04/IMG_20210712_213727-scaled.jpg)
Confirmed bad out of circuit:
![](https://jammarcade.net/images/2024/04/IMG_20210712_212723-scaled.jpg)
Replacing this chip fixes the jerkiness. Game is perfectly playable. Sound and controls tested OK.
Summary :
- 11 DRAMs (SAMSUNG),
- 2 EPROMs,
- 1 74LS193 (TEXAS INSTRUMENTS)
![](https://jammarcade.net/images/2024/04/IMG_20210713_184723-scaled.jpg)
Some months after this repair, I found the proper original Silkworm schematics, scanned it and upload to my GitHub here:
https://github.com/DocteurPCB/schematics/blob/main/Silkworm%20%5Bschematics%5D.pdf
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