PCB Repair Logs – Page 24

Truxton repair log #4

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Aug 122018

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!

Sunset Riders double repair log

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Aug 072018

Recently I had two faulty Sunset Riders (by Konami) PCBs on the bench for repair.The first board came from Portugal:

Board was watchdogging in an endless loop, sign that no valid code was executing by main CPU:

Doing the usual check on CPU/RAM/ROM circuit revealed that a data line of a WORK RAM was stuck low:

Pin was almost shorted to ground:

This is shared with main CPU (pin 1, data line D4) and other devices too.Using a short locator I measured resistance to GROUND of all common points:

The lowest resistance was on pin 7 of a 74LS253 @14B:

The IC failed the out-of-circuit testing:

The board booted up but failed the POST showing a bad device @15B on an upside down screen:

The device concerned is the ER5911 serial EEPROM :

Someone previously replaced and socketed it but managed to rip the rivet of the pad of its pin 4 (which is the data bit output) which lost connection with the rest of board :

Once restored the connection I had to re-initialize the EEPROM:

After this the board successfully booted into game with no further issue.First board fixed.

The second board was in a lot of faulty PCBs I bought:

It booted up but jailbars were present all over the screen:

Lines are a clear sign that something is wrong with the graphics data (in this case the tilemap).I launched a MASK ROM check which found a bad device @16K:

I was about to replace the device when I gave a look on its soldeside and found a deep scratch :

Under a microscope two traces appeared to be severed, they were indeed two data lines of the MASK ROM (pin 13 ‘D0’ and pin 28 ‘D7’).A quick check with a multimeter in continuity confirmed it.

I restored connections with some AWG30 wire:

No more complain of MASK ROM check :

Board 100% fixed and double repair accomplished.

Truxton II repair log

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Aug 032018

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:

Yes, yet another Truxton II PCB fixed!

Tatsujin Oh repair log #2

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Jul 282018

Another board from the ‘portughese’ box : Tatsujin Oh, a great shoot ’em up released by Toaplan and known outside Japan as Truxton II.

Board was booting but sprites were mostly missing and other GFX glitches present too:

There was an obvious reason of this.The custom ASIC ‘GP9001’ (which is the graphics controller of the system) was damaged : some pins were missing, other bridged, two traces going to it were ripped too.

Here’s a close-up under a microscope:

Given the extent of the damage the only possible solution was the replacement of the ASIC which is a very delicate operation (not for everyone…) because of its package (208 pins in a QFP package with very fine pitch).For this purpose I’ve been sent by the owner a dead FixEight PCB as donor: