PCB Repair Logs – Page 19

Pacland repair log #2

Oct 282018

Received a pacland board for a repair which was stuck with a 0 2 0 error at boot.

Normally the middle digit means it’s an program rom error and infact the second prg rom @8D had no sticker and I immediately checked it.

Romident showed it was a Pacland midway rom, but the other prg roms belonged to the japanes new version.

After burning the correct 2nd rom from the jap set I was welcomed with this screen which is the service one.

The dipswitches were all set OFF and after verifying they were working correctly I decided to change all the FUJITSU 74LS257 near them which had dead outputs infact.

In the end all the Fujistsu chips has been changed because faulty: @1L, 2L and 2J!

With good ones changed the game finally booted but the palette was very tinted and the sprites were corrupted:

Verifying the sprites roms 8,9,10 and 11 these were a mess of different revisions, so using a broken pacland I put the matching roms from the new japanese set

Still the sprites were corrupted and eventually I found a bad 74ls86 ( again Fujitsu) @10F

With good one installed I got finally good sprites but still the palette was tinted:

I proceeded on the colour prom section and found that the chip PL1-2 had some outputs dead

Using one from another Pacland board fixed the game 100%

Bucky O’ Hare repair log #4

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Oct 212018

Received from Greece this Bucky O’ Hare PCB :

Owner told me the PCB developed some sound issue so he wanted the ‘054986A’ audio module replaced with a repro of mine.This is what I did but it didn’t cure the problem, the sound samples were corrupted and some of them missing too :

The MASK ROMs test reported two bad devices @A6 and B6:

They are the 16Mbit MASK ROMs that stores PCM samples:

This wass unlikely but possible so I removed and read them resulting in good dumps.At this point there was nothing else to check, the PCM samples data are processed by the near custom ASIC marked ‘054539’ which was most likely faulty.I prepared the board and desoldered the chip with hot air :

Then cleaned the area and soldered the spare taken from a donor board:

Sound was back clear and complete again.End of repair.

Silent Dragon repair log #2

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Oct 122018

Received today this Silent Dragon PCB (a not so well known beat ’em up manufactured by Taito) that I bought as faulty :

According to the seller board played fine but sound was absent.He was right:

Some one tried to replace invain the audio amplifier:

A quick check with my audio probe revealed the issue had a digital and not analog cause.So I went to probe the Z80 audio CPU and found its /INT line always asserted:

This means a maskable interrupt to the CPU was triggered by an external I/O device.This causes execution to jump to a specific interrupt vector (which is some code at a fixed location).Execution can then continue after the interrupt vector routine has finished but in my case the /INT line was LOW all the time so the CPU was not properly running.

A further check revealed pin 21 /RD and pin 22 /WR were shorted each other:

I turned the board over and did a visual inspection on solder side, my attention was caught by this particular:

Under a microscope:

A solder bridge was shorting two vias connected not only to pin 21 and 22 of the Z80 but also to two pins of the ‘TC0140SYT’ ASIC (the sound and interrupt controller)

I removed the bridge with my iron tip and sound was back.Job done

Hellfire repair log #3

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Oct 102018

Another shoot’em up ‘under surgery’.Here we have an Hellfire PCB I received from Portugal:

Board booted into game but sprites were all blocky:

Looking at hardware I could figured out the the parallel data from the four 1Mbit MASK ROMs of sprites are converted into serial by four 74LS166 8-BIT shift registers (one for each ROM)

Probing the 74LS166 @5F revealed the output (pin 13) was stuck high :

While the inputs were active:

I removed the IC:

It failed the out-of-circuit testing :

This lead to an improvement but still not perfect as sprites were missing lines :

Looking again at hardware I could figure out the sprite line buffer is made by eight 2149 SRAMs (1K x 4-bit devices, pin to pin compatible with 2114/2148)

The one @6K was hot to the touch, probing it with a scope revealed weak signals on data lines :

Ther RAM chip failed when tested out-of-circuit :

This fixed sprites completely:

The last issue concerned the sound, it was faint and corrupted:

Looking at sound circuit I noticed a Nec uPC1181H amplifer was fitted in place of the Fujitsu MB3730 that silkscreening suggests :

Although the two amplifiers have pretty same pinout, different is the typical application circuit and power output (14W for the MB3730 and 9.2W for the uPC1181H) so I installed a proper one.Looking at sound section on another same board I noticed three mylar 100nF capacitors were used by factory @C61-C62-C63:

Whereas on my PCB an electrolytic capacitor was installed @C61 and the one @C62 was missing :

I restored the factory condition gaining a loud and crisp sound again.Repair accomplished.

Kicker (Shao-lin’s road) (bootleg) repair log

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Oct 072018

Earlier this year I attended a meetup at UKVAC user Bonehead’s house.
One of the things I brought back with me was an unknown bootleg PCB that a was being given away.
I opted to take this particular PCB because it was 6809 based and I needed something to help me continue work on my Fluke 90 PC software that I started quite some time ago.

This PCB uses the Konami Classic pinout for which I already have an adapter for so following a quick visual check I plugged this in and powered up.

As you can see we have watchdogging going on.
Right next to the 6809 there are two 74LS244 buffer IC’s. A quick continuity check showed that these were connected to the address pins of the 6809.

Probing the 244 at E8 showed that all the outputs were dead. Removing this revealed a broken trace.

At some point in its life there has been a sort here.
I patched the break and fitted a socket and new 244 buffer and checked for shorts before retesting.

Powered up and all was well again.

Confirmed later that the sound is present too and controls are all working.
A quick fix this time.

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