The Toaplan “bonanza” goes on with this Truxton PCB on the bench:
Board was booting into game but sprites were totally scrambled:
This seems to be a common issue on this hardware.Sprites generation circuitry is quite wide with many components involved (an ASIC, counters, four MASK ROM, RAMs, a couple of Bipolar PROMs, etc..).I made a quick check and found nothing abnormal until I probed a 74S20 (Dual 4-input NAND Gate) @5D :
Both outputs were floating:
This was confirmed by logic analyzing :
Chip obviously failed the out-of-circuit testing:
I pulled and it and replaced it with a 74F20 (‘F’ logic sub-family of 74 TTL series has more or less same delay propagation time of the ‘S’ one ) :
Sprites restored and board 100% fixed.
Just a quick note : although the marking of the faulty TTL was partially deleted, I could recognize its brand.It was the only Fujitsu TTL on the board!
Yet another Truxton II PCB (overseas release of Tatsuin Oh) on the bench and always from Portugal :
The board was stuck on boot on a colored striped static screen :
Main 68000 CPU was not running, both data/address bus were inactive.For first I checked the ‘GP9001’ custom GFX controller (QFP 208 pin ) which is a common issue on hardware that use it:
I found some lifted pins:
Reflowing them didn’t lead to any improvement.The board uses the ‘infamous’ custom ‘HK-1000’ custom (the early fragile ceramic revision) which handes inputs :
A closer inspection revealed the IC was damaged, some pins were broken at package insertion so beyond repair:
As said, the ‘HK-1000’ handles inputs but a faulty one can prevent the game to boot because some CPU address lines are used to generate the enable signals for it.I removed it:
Without the custom the board successfully booted up but obviously game was not playable due not working controls:
So I installed two strips of 2.54mm female machined pin headers in order to host a reproduction of mine:
The last issue I had to fix was some rustling background noise:
With the help of my audio probe I quickly figured out the sound was clean before reaching the 2.2K sound potentiometer :
I replaced it and this restored a clear sound.As ‘icing on the cake’ I removed an ugly hack to use a quartz instead of an oscillator and installed the proper part:
These were the issues: sprites were totally absent, sounds was loud and screen was disturbed by some wavy lines
Interferences on video are a common issue on this board, usually they are caused by electrolytic capacitors with increased ESR (especially the filter ones connected to +12V line).On my board the capacitor @C1 connected to +12V was previoulsy replaced:
But who replaced it managed to break the internal connection to GND of its negative terminal, you can see in the below picture that pads (and internal rivets) were ripped off:
The capacitor lost its GROUND reference hence it was not operational.This also explained why sound was loud: the amplifier was oscillating due the missing function of this capacitor (the role of these capacitors in audio circuit is indeed to avoid dangerous oscillations of components) and this affected the video too.I restored the connections, this cured both loud sound and video interferences so I moved on to troubleshoot the lack of sprites.Object data are stored in four 1Mbit 28 pin MASK ROMs :
Probing the address lines revealed they were all stuck low and hence data lines too.Address lines come from outputs of some 74LSALS163 but they resulted good when tested in circuit by my logic comparator.Probing around revealed nothing abnormal until I came across this custom chip (DIP 42 package) marked ‘TOAPLAN-02 M70H005’:
All the pins from from 1 to 21 ( not counting pin 21 which is GND) were toggling but all the ones from 22 to 42 on the other side (except pin 29 GND, and 23-42 VCC) were stuck, these were most likely the outputs.I compared the behaviour on a good board and had confirm that the stuck pins had to be active hence the custom was dead.I desoldered it and I found a ‘GXL-02’ silkscreening under the chip:
I remembered I had a couple of other Toaplan boards I harvested (Hellfire and Out Zone) with same silkscreening on PCB but different marking (”FDA MN53007T0A’) of the custom chip:
Power supply pins were the same so was worth a try.And I was successful, sprites were back:
Later I found that this custom is used on many other Toaplan boards but under different labels.For example, it’s ‘T.T-2’ on Twin Cobra :
Some days ago I had this Truxton PCB on the bench:
Game had wrong colors on some background/foreground objects, like title screen
This part of graphics is generated by a ceramic PGA custom marked ‘NEC D65081R’ which addresses four 1Mbit MASK ROM and read/write data from/to four 62256 static RAMs:
Address bus is daisy-chained between the custom, the four MASK ROMs and the four RAMs, all was in order here.Custom receives data from MASK ROMs and transmits/receives to/from from RAMs on two different bus.When I went to check connections, I found no continuity between pin 17 (D5) of the RAM @18F and the custom.Here is where trace from pin of the RAM goes under the custom (picture taken with a USB microscope)
Infact, if I pressed the custom in this corner, the fault went away.I simply reflowed this dry joint and all came back to normality.
I got this Truxton PCB (export version of Tatsujin) in a recent operator raid:
Once powered it up board showed GFX issue, the sprites were blocky :
Besides, there was some kind of video interference, this is a common issue on this board and usually it’s due capacitors in the audio section, indeed I found a 470uF 16V one with bad capacitance :
Back to the sprites issue, relevant data are stored in four 1Mbit 28 pin MASK ROMs :
I went to dump them and found a faulty one:
Replacing it with one from a donor board didn’t fix the issue therefore I went on in my troubleshooting.Each data bit of the sprites MASK ROMs is fed into inputs of four 8-bit 74LS166 register.I probed them with my logic comparator and led on output pin 13 lit for two of them:
I desoldered the ICs:
They both failed the out-out-circuit testing (obviously they were from Fujitsu) :
Sprites were fully restored :
The last issue I had to fix was that Player 1 Start input didn’t work.The inputs circuitry was previously reworked by someone (note the replaced 74LS240 and some patched traces)
I traced Player 1 Start back from pin 17 parts side of JAMMA connector to an end of a 220 Ohm resistor @R17 whose other end was tied to pin 13 of the 74SL240 @21K :
Signal on pin 17 of the JAMMA connector and on first end of the resistor was high and correctly toggling when pressing the button while was totally missing on pin 13 of the 74LS240.Therefore the only culprit had to be the resistor.Indeed I got no reading measuring it on circuit:
I removed and tested the resistor out-of-circuit having confirm it was opened:
Back to the sprites issue, relevant data are stored in four 1Mbit 28 pin MASK ROMs :
