Nov 102017
 

I had on the bench this Thunder Cross II PCB by Konami:

Many components were removed from the board : one WORK RAM @12D was missing and the other one @11D cracked in half, also the ER5911 serial EEPROM was not there :

The two tilemap RAMs @17H and 18H:

Some electrolytic capacitor in audio section:

The 3.58MHz oscillator @9K (it generates clock for whole sound system)

Also the RAM in sound section was almost desoldered, indeed it came off easily:

With patience I installed all the mising components and powered up the board :

At closer inspection the above error was caused by a broken trace between pin 21 ( address line A10) of the two 6264 WORK RAMs, I promptly patched it:

Now the board went to intial self-test showing two bad devices, both related to sound system.

The one @4F is the ROM containing code of the Z80, the one @5F is its 2K x 8it RAM (previously replaced by me) 

Both were verified as good so problem was elsewhere.Sound system is made of a Z80 which commands a YM2151 FM synthesis chip (used for music) and custom marked’053260′ which plays ADPCM/PCM samples.Lalsty BGM+ samples are sent to a YM3012 DAC which outputs analog sound them amplified by OP-AMP and amplfier.When I probed the YM2151 I found that PIN 21 was dead:

This pin is the serial data output :

I pulled the chip:

It was really bad but also replacing it I still got the error @4F and 5F on self-test.YM2151 datasheet says that in typical application pin 21 is tied to YM3012 but on this board it’s tied to the custom ‘053260’ and then from this to serial data input (pin 4) of the YM3012 DAC.So the ASIC was likely bad.Time to remove and replace it:

Finally board got past the self-test and entered in game with full sound:

But, as you can see from above video, sprites were all garbled.MASK ROM check reported two bad 4Mbit devices @3K and 7K :

Using a logic probe revealed that two address line (pin 6 ‘A3’ and 39 ‘A9’) of both devices were stuck high:

These devices are directly addressed by the ASIC ‘051960’ (working in pair with ‘051937’ which reads data) which from my eperience is not really reliable.So I replaced it:

But I was wrong.At this point, after check as good all connections, it was clearly obvious that the two MASK ROM were bad.Indeed, once removed them, they both failed in same address lines when I read them in a programmer:

 

I replaced them with two pin to pin compatible 27C400 EPROMs and MASK ROMs check no more complained:

Hence board 100% fixed!

 Posted by at 6:56 pm
Nov 092017
 

I bought a faulty Pac-Mania mainly for spare parts but I gave him a chance and tried to repair it

The game was missing sound roms, after replacing them, game booted and you could play but the screen was totally a mess.

After some blind testing I started test all socketed custom chips and rams against new ones and I eventually found the culprit

in the “text” ram @L5!

It was so bad that it totally covered the screen with junk graphics

Replacing it fixed the game 100%

Nov 092017
 

Got this Pacland, Sidam version, in mint conditions  for a repair

The game had some color bitplanes of the sprites shifted to the left as you can see from this pic

The sprites are handled by CUS29 and there are two 2149 rams connected.

Piggybacking a good 2149 ram on top of the one @3T restored good colours

Testing it out of circuit confirmed it was bad

The game had no other faults and was 100% fixed

Nov 082017
 

Received this quite rare Hard Puncher (on Konami Twin16 hardware) for repair:

PCB failed all the time the self-test showing a bad device @10G on CPU board and then resetted, this in an endless loop:

The involved device is a Mitsubishi M5M5165 (8K x 8-bit static RAM) compatible with 6264 :

Its data bus showed no activity:

The chip failed the out-of-circuit test each time in a different address location:

With a good RAM the board successfully booted into game:

But speeches were missing, here is a comparison with a MAME recording:

I quickly pinpointed this fault in a missing 640KHz ceramic resonator, this is for generating clock to the uPD7759 ADPCM speech synthesizer IC.I took a spare from a dead Sega System16B motherboard:

Job done.

 Posted by at 9:13 am
Nov 042017
 

The second of Alex’s board for repair is Donkey Kong Junior.
This board booted to static screen that wouldn’t sync. This ended up being a broken 30k pot on the H-Sync.

As I don’t currently have and 30k or 50k pots I opted to temporarily fit an 18k resistor to the video PCB to let me move on.

The game now booted to a static screen of garbage but when touching the Z80 CPU it booted. The socket looked old and a bit crusty so I replaced it.
The game now played but there was a lot of garbage still on the screen.

I hooked up the Fluke 9010 and did some basic reads and writes to the video RAM that sits between address 0x7400 – 0x77ff.

Clearly bits 0 and 1 were stuck low.
Using the schematics I started checking at a 74LS245 at location 6A which buffers the databus.

Straight away I found although the signals were going to the chip the outputs on DAT0 and DAT1 were floating.
As the outputs were floating I tested by piggybacking a good 245 chip and everything came up good.

Replace the 245 and fitted a new one.

Tested the game and all sound and controls work too.

Another one fixed.

 Posted by at 2:52 pm