Got this original Taito (licensed to Romstar) Arkanoid PCB for repair:

Board uses the Taito Classic pinout (used on other games like Bubble Bobble, Elevator Action, Jungle King) so I had to build a proper JAMMA adapter:

 

On power up I was greeted by this static screen:

The string “WOVO VEM EVVOV” reminded me “WORK RAM ERROR”.I had confirm of it opening one of the program code ROM with an HEX editor:

The WORK RAM is located  @IC15 in form of a 2K x 8-bit device but piggybacking it had no changes.There are other two 2016 static RAMs @IC57 and IC58  :

When I went to probe the one @IC58 I found the data bit 2 (pin 11) stuck high:

This is tied to pin 9 of a 74LS245 @IC42 for exchanging data with the other one @IC57 which, according to MAME memory map, is the VIDEO RAM shared with Z80 main CPU:

1   1   1   0   *   *   *   *   *   *   *   *   *   *   *   0       RW  2016 SRAM@IC57
1   1   1   0   *   *   *   *   *   *   *   *   *   *   *   1       RW  2016 SRAM@IC58

 AM_RANGE(0xe000, 0xe7ff) AM_RAM_WRITE(arkanoid_videoram_w) AM_SHARE(“videoram”)

PIN11 of the transceiver was, instead, properly toggling :

Piggybacking it restored correct error message:

I pulled the 74LS245 and it failed the out-of-circuit test exactly in the involved gate:

Replacing it fixed the board completely.

Another board from the box of the “death”: The Simpsons

It immediately appeared to be a “desperate case”, board was heavily “harvested”, many components were missing:

A smashed TEST switch too:

I tried to power up the board and obviously it didn’t work, it was  in an endless loop:

Summing up, these were the missing/broken components : 

• 6264 RAM @16G
• 3.579545MHz oscillator @4G
• ER5911 serial EEPROM @12C
• MB3722 amplifer plus electrolytic capacitors @C21 (1000uf 16V), C16 (1000uF 16V), C114 (330uF 16V)
• momentary switch @16A  

I reinstalled the RAM, the oscillator and the EEPROM (temporarily omitting components in audio circuit)  and board showed the self-test reporting bad devices @12C (ER5911 serial EEPROM), 6G (sound Z80 code 27C010 EPROM) and 7G (2k x 8-bit SRAM of sound system)

I cleared the first error by re-initializing the EEPROM (holding down the TEST switch while powering up the board) 

As for the other two errors, I dumped the EPROM @6G and code didn’t match any existing MAME set so I reprogrammed the device with correct code.This cleaared the error but the one regarding the device @7G was still present.Probing the device (a Sony CXK5814, a 2k x 8-bit static RAM compatilbe with 6116) revealed unhealthy signals on data lines:

Once removed, the chip failed the out-of-circuit testing:

Finally the self-test no longer complained so board booted into game but colors of some backgrounds were wrong and sprites were mssing parts:

The MASK ROMs check reported a bad device @16L, this is a 8Mbit one containing sprites data:

 

I replaced it with a 27C800 EPROM but with no luck so I focused on the background colors issue.The hardware uses an ASIC marked ‘053251’ which is responsible of palette and priority:

The chip outputs 11 bit of palette index called ‘CO0-CO10’ on schematics:

Probing the outputs with a scope revealed bad signal on pin14 ‘CO4’ (healthy signal on the left for comparison)

I removed che custom and replaced it with a spare take on a donor board (Premiere Soccer)

This fixed the color issue but sprites were always wrong :

and device @16L was still reported as bad:

Schematics don’t cover this part of circuit but I knew the design.The two ASICs marked ‘053246’ and ‘053247’ work in tandem, the first generates the address lines to the sprites MASK ROMs and the latter read and process their data:

I checked connections between the ASICs and MASK ROMs, no problem found.Actually the data lines from MASK ROMs are not directly tied to the ‘053247’ ASIC but there are some 74LS374 in the middle (two for each ROM) which latch data bits.Piggybacking the ones @12K and 10K restored partially the sprites.I desoldered the first and it failed the out-of-circuit test:

 

This improved sprites but not yet perfect :

So I removed also the other 74LS374 @10K, it failed too!

This fixed the sprites issue completely.As for lack of sound it was only matter to fit the missing MB3722 amplifer and electrolytic capacitors  @C114, C21 and C16.

Another board torn from the darkness, long live to it!

Received some days ago a box of faulty boards for repair.There was a clean Sunset Riders PCB:

Game played fine except for sound since samples were only noise (music was fine instead):

Sound samples are stored in a 8Mbit MASK ROM @1D:

MASK ROMs check reported it as bad:

I was sure device was really bad (Konami ones are well known to be prone to failure) so I removed it :

But it turned out to be good instead since reading it ended up in a good dump and also replacing it with a programmed 27C800 EPROM had no effect .

Sound samples circuit is very simple, the ASIC ‘053260’ (a custom PCM/ADPCM sound chip) addresses the MASK ROM @1D and plays its data:

No other component is direclty involved so most likely the ASIC was the culprit.I removed it :

Took the spare one from a scrap Asterix and soldered it back on my board:

Success!MASK ROMs check reported now a good device @1D hence board 100% working and fixed :