Aliens repair log

Recently I got for repair an Aliens PCB, a great side-scrolling shooter arcade game developed and published by Konami in 1990.Board was in good overall condition :

But on power up I was greeted by a flashing blank screen along with a clicking noise suggesting that board was resetting in an endless loop due to the triggered watchdog circuit :

Hardware uses a custom CPU in PGA package marked '052526' :

Probing it revealed the 'DTACK 'pin was never asserted ('DTACK' is an input signal that informs the CPU that data is ready to be read from memory. It stands for "Data Transfer Acknowledge.")

Schematics shows this signal is generated by a 74ALS74 @F11.Going upstream I found the signal named 'IOCS' was stuck high: :

The 'IOCS' signal comes from one of the two PAL16L8, precisely the one marked '053327' @D20, this is the main address decoder as schematics shows :

PLDs (GAL or PAL)  are usually quite reliable but in this case it was the first suspect so I removed the chip and read it in my custom PAL dumper.The result was quite obvious, most of outputs were recognized as invalid or fixed high (like pin 14 which generates, indeed, the 'IOCS' signal)  :

 

Luckily this PAL was dumped by me time ago so I programmed the fusemap (downloaded from the JAMMArcade PLD archive) onto a GAL16V8 :

 

I powered up the board again and it booted up into game :

I played some games and no further issues were present so this was another successful repair and another great game preserved.

Namco '6xA1' reproduction final revision

Another small update.

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 :

Namco '6xA1' replacement

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 :

Irem 'M72-ROM-C' board reproduction

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.

Enjoy!

P-47 - The Freedom Fighter repair log and Jaleco 'JK-01' - 'JK-02' reproduction

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.

Konami '051550' reproduction final revision

Just a quick update about the reproduction of the Konami '051550' custom IC I made time ago :

Konami '051550' reproduction

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.

 

Konami '056602' reproduction

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 :

Konami GX System

Konami GV System

 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 :

 Konami '056602' soundboard

 
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 :

Prehistoric Isle in 1930 repair log

Recently I found in my pile of PCBs an original Prehistoric Isle in 1930, I remember I bought it as faulty on eBay some years ago but never had the chance to look at it for repair.Recently I decided it was time to finally do it.Board was in good condition :

As always I do before powering the boards up for first time I made some checks with a multimeter and found that there was almost a short between GROUND and +5V, only 9.7 Ohm of resistance exactly :

 The PCB is actually a two stack one with a top CPU board and bottom VIDEO one hence I separated them and figured out the short was in the bottom one :

As said, this was not what is called a 'dead short' with zero Ohm of resistance across GROUND and +5V , therefore it was impossible to locate it with normal equipment, whatever you are gonna to use (multimeter, ohmmeter, ESR meter) you would obtain always the same value of resistance all over the board.

At this point I had two options : desoldering all the components one by one until catching the almost shorted one(s) or resort to some special equipment that was able to locate them with a certain precision.After some reseraches I came across this tool, the 'LeakSeeker 89' from EDS Inc. :

 

It's essentially an autoranging fault locator (with a range from zero to 300 ohms) that can locate not just shorted, but 'leaky' parts as well.You can read more about here :

LeekSeeker 89

Here's how it works .

 

It was just what it suited me so I ordered a kit which came in the mail after some time.The assembing was pretty easy and quick :

After some practice with this equipment I was able to narrow the field of search of the short in this particular area of the board :

I started to removed some ICs in this area :

I found a couple of  faulty 74HCTLS157, both were from Samsung manufacturer.This lead me think they perhaps belonged to the same bad lot so I pulled the others in the involved area.Some were good but other three were bad for a total of five ICs of same type :

All were 'leaky' with low resistance between power supply pins, the 'LeekSeeker 89' made his job, it was really worth the buy, money well spent!

I installed good chips and powered up the board for first time.To my surprise it booted into game 

I played some games with no other issue found.So this was another succesfull repair and a great shoot 'em up added to my collection.

Toaplan 'GXL-02' reproduction

 The 'GXL-02' is a custom chip (in DIP42 package) found on most Toaplan arcade PCBs but you'll never encounter it with this part name but instead diffrently marked.Here's an overview:

"FDA MN53007T0A" on Hell Fire, Out Zone, Fire Shark :

‘TOAPLAN-02 M70H005" on Truxton/Tatsujin :

‘T.T-2’ on Twin Cobra/Kyuukyoku Tiger :

‘WT2’ on Wardner/Pyros :

 ‘L-02’ on Sky Shark/Hi Sho Zame :

 

 ‘12.02’ on Rally Bike/Dash Yarou :

But, despite different labels, the silkscreening under the chip says always 'GXL-02' .

Unlike the 'GXL-01' (already reproduced by me  Toaplan 'GXL-01' reproduction ) that generates backgrounds, the' GXL-02' handles sprites acting like a big counter.As usual, for my reproduction I took into account some bootlegs in order to study how the functions of this custom chip had been reversed by bootlegers.Unfortunately none of them was a complete TTLs implementtion of original chip but they gave me for sure hints on how the chip worked.

After some time spent adapting the designs from different bootlegs replacement boards I was able achieve a TTL prototype working for all games, here's testing on an Hell Fire PCB  :

The next step was pretty easy since I had a valid design in my hands so I engineered a proper board that was as much compact as possible without the use of modern programmable logics (CPLD or FPGA) but simple surface mounted TTL gates.The result was pretty good :

 The replacement worked fine on all PCBs I could try :

Hell Fire .

Out Zone :

 

Rally Bike :

 

Wardner/Pyros :