Another shoot’em up on the bench and always a board coming from Portugal : Double-Wings produced by Mitchell Corp. in 1993 (but hardware is clearly marked Data East)
The board booted into game but had a color issue, the screen was all blueish :
The brief POST showed an error related to palette RAM:
After a quick look at PCB I pinpointed the palette RAMs is two 6116 (2K x 8-bit devices)
When I went to probe with my scope the lower one @5F I found some stuck data lines:
I pulled the chip and tested it out-of-circuit.It failed:
Installed a fresh RAM on a socket :
This fixed the issue and board completely.Another repair accomplished.
Got this Explosive Breaker PCB (an unusual shoot’em up from Kaneko) from Portugal for a repair.Board was in good condition but showed some sign of previous rework especially on SMT devices :
On power up the self-test seemed to be successully performed but then an error occured and the board resetted in an endless loop:
Inspecting the board I found that the custom IC marked ‘VU-001’ (involved in Serial EEPROM and dispwitches handling) was burning hot :
The IC seems to be used on very few other Kaneko PCBs but we looked around and found a donor (Magical Crystals, a maze game) which runs on identical hardware:
I replaced the custom with the spare :
Board finally booted into game but screen was blueish:
A predominance of the blue color means that red channel has troubles or is missing.The RGB colors come from the emitters of three NPN transistors:
Probing the base of the red transistor revealed no signal hence the problem was upstream:
The base is tied to the nearby custom marked ‘699205P’ .
As said before all the SMT devices were previously reworked, also this one showed signs of hot air reflow.Inspecting it with a microscope revealed a solder bridge shorting two pins:
I fired up my soldering iron and removed it, this restored the correct colors and fixed board competely.Job done.
I had this original Silkworm PCB (manufactured by Tecmo in 1988) in a trade some years ago :
I didn’t know the status of the board since I never looked at it.Quite confident I powered it up but I was immediately disappointed, a solid static blank screen was all I got:
While I was visually inspecting the board I noticed the 28 pin brown SIL hybrid module marked ‘MA7053’ was a bit wonky:
I slightly wiggled it and it fell off:
I installed some 1.778 female pin headers on the PCB:
and patiently soldered the component on a strip of correspondent male headers:
In this way I got the board booting but with severe graphic faults.Color were wrong, sprites flashing (it’s hard to capture this issue with a camera), vertical lines through screen :
I decided to troubleshoot the sprites issue for first.Studying the hardware I figured out that the line buffer is made of twenty 4164 (64K x 1-bit) dynamic RAMs located on VIDEO board :
Some of them were extremely hot to touch and many showed stuck bit on output:
I pulled them all one by one:
Nine of them failed the out-of-circuit testing:
The graphics were correctly drawn now but the colors still wrong :
Tracing the three colors back from JAMMA connector I figured out the final part of the RGB DAC circuit where I noticed the lack of three resistors @R10-R8-R12 :
I compared my PCB with some pictures online and I had confirm that the three resistors were really missing on my board:
I didn’t know the correct value of these resistors and schematics were not available so I looked at Rygar ones which runs on similar hardware, they were 120 Ohm as part of the R-2R resistor ladder circuits used as RGB DAC:
I installed the resistors :
This fixed board completely:
Mitsubishi ‘MA7053’ reproduction
After repaired the PCB I thought this was a good chance to study a replacement of the ‘MA7053’ custom SIL.As often I do in my reproductions I looked at how possibly the custom was re-engineered.I could find two replacement daughterboards.One used on a bootleg PCB :
The other one was from an original Tecmo board (pictures kindly provided by ‘monsterlair’, thanks again to him)
Design were slightly different but they both have same functionality.Technically speaking the ‘M7053’ provides interface between the Z80 main CPU data bus and video memory latching data too.After figured out schematics of the two daughterboards I re-engineered them with surface mounted devices ending up with this result :
Installed on PCB for testing:
Both designs perfectly works on my newly repaired Silkworm :
The ‘MA7053’ is used for sure on these PCBs:
Gemini Wing
Rygar
Silkworm/ Back Fire
But it could be present also on other Tehkan/Tecmo boards so any addition is welcome from all of you arcade collectors/enthusiasts.
Received from Germany this mint Liquid Kids PCB (on Taito F2 hardware) for repair:
Board was working fine except for sprites, they had jailbars through:
First of all I dumped the two 4Mbit MASK ROMS which store sprites data, they turned out to be good.This part of graphics is almost entirely generated by a custom ASIC marked ‘TC0200OBJ’ which showed some sign of previous rework on my board :
We can see pinout and implementation of this custom in the Final Blow schematics :
Probing with a scope its outputs data pins revealed some unhealthy signals (shown on the right on the below snapshot, good on the left)
