Received for repair this original Wonder Boy III – Monster Lair PCB (on Sega System16B hardware)

Board booted into game but sound was missing and some objects glitched :

I decided to troubleshoot for first the lack of sound.The amplifier was previously replaced as well as some electrolytic capacitors:

Using my audio probe I could figure out that the lack of sound was not caused by a fault in the analog circuit but it had a digital nature so I went to check the relevant circuit made of a Z80B CPU, a 6116 SRAM, a ROM and a YM2151 (plus a UPD7759 for speech samples) and I found that pin 15 (data line D5) of the RAM was silent as well as on the respective data bit of the Z80 and the YM2151 :

But it was toggling on the ROM (a 27C512 EPROM) which lies on ROM board :

 There was clearly a broken trace somewhere so I run a jumper wire from the RAM to the ROM:

This restored the sound.

Now the sprites issue.Relevant data are stored in eight 27C512 on ROM board :

I dumped the devices and my programmer complained about a bad contact on pin 9 of the EPROM @B2 and pin 16 of the one @B7:

At a closer inspection it turned out the pins were cut so they didn’t make a good contact into sockets:

I rebuilt the pins and this fixed the sprite issue.Board fixed.

Received for repair this original The New Zealand Story PCB (one layer hardware revision)

Board played fine except for this issue concerning background graphics, they had jail bars though :

All GFX data are stored in eight 1Mbit 28 pin MASK ROMs :

I dumped them starting from the one on the right labeled ‘B53-01’ :

And my programmer complained about a bad contact of pins 18-19 (which are data lines)

As said the device is a 1Mbit 28 pin MASK ROM which no direct replacement exist of, the only option is to adapt a 1Mbit 32 pin EPROM (better with non-JEDEC pinout), that’s what a made :

Perhaps not the best looking solution but it fixed board completely.Job done.

 

P.S.

This repair inspired me so I made my own design to adapt a 1Mbit 32 pin TSOP Flash ROM to the 28 pin 1Mbit MASK ROM pinout:

 

Received this Vapor Trail PCB for a repair :

Board had two noticeable issues, the sound samples were corrupted and sprites glitched like if part of them were floating on screen

I decided to troubleshoot for first the sound issue.A quick visual inspeaction revealed a 470uF electrolytic capacitor was missing in audio section:

But it was just the one which filters the +12V so reinstalling it didn’t cure the issue.

PCM samples are played by two OKI MSM6295 on main PCB while data are stored in two 27C010 located on ROM board:

I dumped the devices and they matched the MAME ROM files:

ROM_REGION( 0x40000, “oki1”, 0 ) /* ADPCM samples */ ROM_LOAD( “fj06”, 0x00000, 0x20000, CRC(6e98a235) SHA1(374564b4e494d03cd1330c06e321b9452c22a075) ) ROM_REGION( 0x40000, “oki2”, 0 ) /* ADPCM samples */ ROM_LOAD( “fj05”, 0x00000, 0x20000, CRC(39cda2b5) SHA1(f5c5a305025d451ab48f84cd63e36a3bbdefda96) )

But then I remembered I repaired another same PCB which had only one EPROM for audio samples whereas the other socket was empty.Other pictures found on the net confirmed this too like this one taken from ‘system11’ blog:

So I removed the one @1F and sound was fully restored.

Now the sprite issue.Hardware used the custom ASIC (in QFP160 package) marked ‘MXC 06’ which generate objects  :

We can see its pinout in the Oscar schematics:

Since the ROM board covers entirely the ‘MXC 06’ custom ASIC denying me any access to probe its pins I decided to replace it given also the fact there is almost nothing else involved in sprite generation  :

I took the spare from a dead Sly Spy/Secret Agent PCB and soldered it pin by pin with the iron tip:

When I powered the board up again, the glitches on sprites were gone so I could declare the board as 100% working.End of job.