Jul 122019

Got in the mail today this Tatsujin Oh PCB (japanese release of Truxton II), a great vertical shoot ’em up released by Toaplan in 1992 :

The board was bought on eBay and according to the seller it didn’t accept credits.But actually, when I powered it up, it booted to a ‘TILT’ message screen and then kept resetting in an endless loop:

I have experienced this issue many times and the culprit was always him,  the “infamous” ‘HK-1000’ :

This custom IC handles all the inputs including SERVICE, TEST and TILT and it’s a very prone to failure part, especially the first ceramic revision (like the one present on this board) cracks very easily or goes internally bad.As you may know, I have done a reproduction of this custom IC so I installed a unit after removed the original part and put some round machine pin headers :

Board booted now into game and correctly played but audio was loud, especially explosions and other sound FXs :

As you can see in above video I could not even adjust the volume by acting on the 1K potentiometer :

So I removed it:

It was broken as it fell off in pieces :

I installed a good one:

Sound was fully restored, board 100% fixed.End of today job.



 Posted by at 3:55 pm
Jul 112019

Received some days ago an Out Zone PCB for repair :

Board was marked as faulty with player 2 stuck in down direction and so it was when I powered it up:

Probing the P2 DOWN pin (19 solder side) on the JAMMA connector revealed it was floating as if it was not pulled-up :

Checking the relevant pin of the 4.7KOhm resistor array (which acts as pull-up) gave me a value of 3.8KOhm, there was something pulling it low:

The signal from the resistor array goes then to pin 4 of a 74LS240 @15M whose resistance to GROUND was only 2.2KOhm:

I removed the IC :

Although the chip was tested good out-of-circuit I replaced it :

This fixed the issue with player 2 but the board suddenly died while I was testing it giving me a solid black screen on power up.From the top of my experience with this hardware I know that the audio circuit must be running otherwise the board will not boot.When I checked the Z80 audio CPU I found the clock input stuck low :

The clock is derived from a 28MHz oscillator:

The scope confirmed there was no periodic signal from its output, ther oscillator was dead:

I pulled it out :

Fitted a spare:

Board booted up again with no further issues.Repair Accomplished.

 Posted by at 9:51 am
Jul 042019

Received a Parodius DA! PCB for repair, a shoot’em up and second title in the Parodius Series produced by Konami :

Board booted up and game was fully playable with sound but sprites were wrong:

First of all I launched a MASK ROM check which reported two bad devices @K2 and K8 :

They are, indeed, 4Mbit MASK ROMs that store sprite data processed then by the near ‘053244’ and ‘053245’ custom ASICs :

The result of the check didn’t imply the devices were really bad but also that they could be not reached.So I went to probe them and found that pin 1 of the MASK ROM @K2 was floating while same pin of the one @K8 was active :

Pin 1 is the highest address line of the MASK ROM and should be in common between the two devices whereas, at quick check with a multimeter, it was not.Hence the trace to pin 1 of device @K2 was interrupted somewhere.I added a jumper wire on solder side:

This did the trick, sprites were restored and board 100% working again.Repair accomplished.

 Posted by at 6:47 pm
Jun 272019

I had a couple of original Capcom ‘1942’ PCBs lying around which I never tested due to the lack of a proper JAMMA adapter (game uses an unique pinout which is not the Capcom Classics one).Recently I had chance to build the adapter and try the boards out, it turned out both were faulty.

The first set was in good shape in its CPU board :

And VIDEO board:

It even booted up and played with sound too but sprites (planes) were totally absent:

The faulty was obviously located on VIDEO board so I went through schematics and found a part of the object circuit highlighted with an handwritten note saying “NO PLANES”

The circled section concerned two NAND gates of a 74LS00 @N8 which generates two signals labeled ‘1WR’ and ‘2WR’.When I probed the inputs I found pin 9 and 4 stuck HIGH:

These inputs come from outputs of a 74LS139 @N10 which had its pin 1 floating:

Pin 1 is the enable input of the decoder and comes from output pin 5 of a 74LS174 @N11 :

Pin 5 of this 74LS174 was indeed floating, stuck at undefined voltage level of +1.64V :

But the input pin 4 was active :

This is a typical way of failure of Fujitsu TTLs and the part was from this manufacturer hence , sure enough, I removed the chip.It miserably failed the out-of-circuit testing:

Replacing it restored the sprites :

First board fixed.


The second set was in good shape too :

But it booted to a static garbage screen :

Probing the Z80 main CPU revealed clock input (pin 6) was stuck high:

With the help of schematics I traced the clock input back to pin 7 of a 74LS174 @H6 located on CPU board, chip was again from Fujitsu :

Input pin 6 was correctly receiving a 3 MHz signal:

I made piggybacking with a good known IC and board succesfully booted into game:

Chip obviously failed the out-of-circuit testing:

Replacing it fixed board completely.Double repair job done.

 Posted by at 11:08 pm

Namco System 1 ROM boards repair log and ‘CUS95’ reproduction

 PCB Repair Logs, Reproductions  Comments Off on Namco System 1 ROM boards repair log and ‘CUS95’ reproduction
Jun 072019

Recently I received a pile of faulty Namco System 1 hardware.I’ve been sent boards grouped by type because, as you may know, it’s a complex system made of a smaller CPU board and a bigger ROM board.I started to troubleshoot the latter.Three of them were tagged as “working but with sound issue” when tested with the same Pac-Mania ROM set :

The issues went from corrupted sound to lack of some music tracks :

Using an audio probe I figured out the sound was properly coming out the YM3012 DAC but then got corrupted before being amplified.In the middle there are two TL084 quad OP-AMPs :

This part is well known to be very prone to failure especially the ones made by Texas Instruments manufacturer like in this case so I removed them all and they failed the out-of-circuit testing :

Replacing them with good ones restored full sound but while I was testing the boards I noticed some inputs were not working on one.A quick visual inspection revealed this :

The custom resistors/capacitors array marked ‘CUS95’ was cracked in half.Not having a spare I decided to analyze the part and reproduce it :

Three boards were fully functional now.The last one had also other issues besides sound not properly working as most of graphics were missing replaced by garbage,  sprites were barely visible :

The tilemap generation is handled by the custom ASIC ‘CUS123’ (plus the ‘CUS133’ on CPU board) which generates the addresses to the character ROMs:

It was most likely faulty so I replaced it :

This restored the graphics and left me with the sound issue to fix, music were completely missing on this board:

Replacing the two TL084 OP-AMPs didn’t do the trick this time so I went to probe the rest of circuit.I found that the 78L06 voltage regulator that provides +6 Volt to the YM3012 was outputting only +2.7 Volt :

Replacing it restored full sound.Namco System 1 multiple repair accomplished.


 Posted by at 11:27 pm