Some time ago I designed a device that can replace all the three Namco MCUs marked '60A1' , '63A1' and '64A1', you can read more about in my previous post :
The replacement was working fine but I later realized that it could not fit well on certain boards due to its dimensions so I made a more compact board layout using smaller surface-mounted packages.Here's a side-by-side of the new board with the orginal custom '64A1' used on Namco System 1 games :
Like the previous revision also this last one can substitute the three Namco '6xA1' MCUs, you can simply select which one you need by setting a 2-way DIP switch located on bottom side :
Here's the replacement set as '64A1 and installed on a Splatterhouse conversion PCB :
Here's another reproduction I made lately.This time not of a custom IC but an entire board, more exactly the top one (silkscreened 'M-72-ROM-C') from R-Type, the horizontal-scrolling shooter arcade game developed and released by Irem in 1987 and running on 'M-72' hardware.
I tried to stay as much closer as original board (that contains program code and sprites data) so everything from the original layout was kept including silkscreening. mounting holes and so on.The only variation I made was to use surface mounted by-pass ceramic capacitors on bottom side instead on thru-hole ones on top.
Here's how the replica looks (with the original ROM set mounted) :
Here's a side-by-side comparison of original board on the left and reproduction on the right
To point out that the reproduction was done by me with no cloning program or other automated process but only by manual tracing of the original board using a multimeter and then comparing my schematics with the available ones.
Got for repair a faulty original 'P-47 - The Freedom Fighter' PCB, an horizontal shooter originally developed by NMK and published by Jaleco in 1988 running on Mega System 1 hardware :
The board was dead, no sign of life, only a steady black screen.First of all I checked with a logic probe if the RGB colors were active, they were all stuck :
I traced the signals back to the cutom SIL marked 'JK-02' :
This part is basically an RGB DAC (like the Taito 'TC0070RGB' for example), doing some check with a multimeter I found its pin 15 was almost shorted to GROUND :
Pin 15 is the RESET input signal for the internal circuitry.I traced it back to pin 23 of a near surface mounted IC (a custom gate array from NEC) :
I lifted that pin and the short was still present on the 'JK-02', this confimed it was really bad.So I replaced it with a same part taken from a donor board (but with the intention of reproducing it at a later time).This gave me back the RGB output but all I got was a static garbage screen :
Checking the 68000 main CPU revealed no proper /RESET signal, there was no transition on boot from a LOW to HIGH logic state :
The signal is generated by a typical circuit based on the 'PST518' voltage monitor IC :
Then it's inverted by a Schmitt trigger (74LS14) but my logic probe detected no signal on this IC :
A closer insection revealed a broken trace from the near 10uF electrolytic capacitor to the 74LS14.The role of this capacitor in this reset circuit is primary because, when the power supply voltage
drops below a certain threshold, it suddenly discharges generating thus
the required reset signal.I restored the connection and finally the board booted into game but sprites were almost missing, they were displayed as a few lines :
Studying the hardware a little I figured out the part of the circuit that acts as sprites line buffer, there are four 62256 (32K x 8-bit) static RAMs:
I probed these RAMs with my scope, all of them had unheathy signals on data lines :
I removed the first two chips :
They failed the out-of-circuit so I replaced them.This improved things, sprites were more visible but not yet perfect.So I pulled the other two RAM chips, they were bad as well :
Replacing them restored sprites completely.Playing some games revealed a new issue, controls were not working, both players' airplanes moved downward by themselves and crashed :
This is a common problem on Jaleco Mega System 1 hardware because inputs are handled by some custom SIL marked 'JK-03' whose legs most of times bend and lose connection with the internal circuitry.This was also my case, they were not in great shape :
I was able to salvage two of them but the third one was damaged beyond repair so I replaced it with a reproduction of mine :
I was about to archive this repair as successful but playing the game I noticed some sound samples (like explosions, power-ups) were missing :
The samples are played by two OKI MSM6295 located on ROM board :
"Listening" with an audio probe the analog outputs of the two MSM6295 revealed the missing sounds were present and correctly played by one of them but then lost somewhere.Tracing the output back lead me to the cause :
A 10uF electrolytic capacitor (that routes the analog signal from the OKI MSM6295 to the motherboard) was ripped.Fitted the missing part restored full sound and fixed board completely.Another repair successfuly accomplished.
Now the reproduction section of this repair.
As said above, the 'JK-'02' custom SIL was bad and, after replacing it with a same part, I later reproduced it :
Testing of the 'JK-02' reproduction :
The Jaleco Mega System 1 hardware uses a third custom SIL marked 'JK-01' which is involved in graphics generation:
I thought it was good for hardware preservation to reproduce this as well so I made it:
Testing of the 'JK-01' reproduction :
Now the set is complete and we have a replacement for all these fragile Jaleco 'JK-0x' custom SIL.
The replacement is working fine but, when I did it, I intentionally omitted a part of original circuit that handles the coin counters/lockouts and gave priority to the main functions of this custom IC, namely generating the master reset and acting as watchdog timer.Lately I decided to complete the reproduction by implementing what was missed from the original part so here we are!
This is the final revision of my Konami '051550 reproduction, no further ones will come because this is now a perfect 1:1 replica of the original custom IC.Outwardly not much has changed :
But you will now be able to properly use coin counters/lockouts in your arcade cabinets.
The Konami '056602' is another ceramic audio module along the lines of the more well known '05498A' and '054544.You can find it on 'GX/GV' systems hardware :
It's located in the audio section just near the main amplifier :
As said, the part has a fragile ceramic package (of 38 pin with an unusual 'ZAG-ZAG' configuration) hence it can easily breaks off in pieces like happened to the author of the below picture (credits to 'AstroX' on AP forums)
Technically speaking the Konami '056602' is essentially a DAC (Digital to Analog Converter) which , indeed, converts into analog the digital audio signals from the board, then it does pre-amplification and lasty output them to the amplifier and audio headers on the board.All the other components are passives, mostly ceramic capacitors and laser trimmed print resistors but, like the "cousins" '054986A' and '054544' audo modules, there are some SMT electrolytic capacitors on the other side of the module :
These capacitors with aging can leak corroding the circuit around or have their ESR value altered causing scratchy sound or total lack of it.'Seb' from RepArcade posted a useful maintenance tutotial (with capacitors chart) on his blog :
Given all these premises plus the fact someone in the past asked me to take this audio modue into account, a reproduction was certainly worth so I accepted the challenge.The main obstacle was, besides drawing the schematics of the module, identyfing all its components as well as measuring the precise values of the passive parts (some hidden like some printed film resistors), you can't go wrong otherwise the reproduction will not sound like the original.I made no prototyping and routed a first board layout that was manufactured and shipped to me in some days.The assembling took some time due to the large number of components involved (some were obsolete and hard to find) but I managed to complete an unit ready for testing :
The "debut" was successful, no design mistakes were done and the reproduction sounded exactly as the original module.Here is testing on my PCBs :
