Jul 242016
 

Got this board from Muddymusic.
Board was filthy when I got it and most IC legs were a nice shade of green. I decided to clean this up first.
20160722_194239

After a good clean the board came out OK, not great but definitely much better. I noticed that a socketed RAM chip had one of its legs hanging out the side of its socket.
20160722_194750

Not sure what effect this would have but I reseated it properly before powering it up.
I replaced all of the single wipe sockets on this board as I really don’t like them.
20160723_130630
20160723_115551

Next up was the power up test and I was greeted with a yellow screen which eventually turned mostly red and stayed that way. I could see the game was booting at least.
20160722_194824

From this point I can be sure the palette circuitry was at fault. Looking at the schematics you can see there are 2 x CXK5856 RAM chips responsible for the palette RAM.
t2_palette

In my experience these RAM’s have been the most unreliable so I desoldered both of them straight away and both of them failed spectacularly when tested out of circuit.
I replaced them and fired up the game.
20160723_151652
20160723_151700
20160723_150306

All seems to be working fine now.
Also dumped all the PAL’s from this too and hopefully will be getting them tested soon.

Jul 212016
 

Got this Devil World PCB as non working. This game is running on a Konami Twin 16 hardware. It is a two layer board with the first one devoted to CPU/sound and the second one to GFX/video. The two faulty/replaced chips were on the video board and are highlighted in red.

devilworld1

Luckily the board was booting and got stuck on the RAM/ROM test screen with ROM #18 reported as bad (chip #1 on the board picture above).

devilworld2

That ROM is part of a 4 ROMs row which contains the GFXs. They are 40 pins Konami chips and looking in MAME I could see that they were 512kb MASK ROMs. I tried dumping it with my programmer but was unable as it found one dead pin. Compatible EPROMs for these are 27C400 so I burned one and replaced it.

The game was now booting but with a color problem on some tiles.

devilworld3 devilworld5

After a deep look at the video board I could find a Fujitsu 74LS153 located at 10H (chip #2 on the board picture above) with floating outputs (while inputs had healthy pulsing signals). I piggybacked it and got everything corrected. I desoldered the faulty one, put a socket and replaced it. Board is now working perfectly.

devilworld4 devilworld6

Jul 182016
 

Received this Out Zone PCB for a repair:

DSCN3862

Actually board was a factory conversion from a Zero Wing board (hardware revision ‘TP-015’).When I powered it up, I got nothing of screen, neither the  black and white wavy lines sign of the system being initialized like it happens in this Toaplan hardware :

Probing the 68000 main CPU releaved it properly received /RESET signal as well as clock was present.As usual I did my check on CPU/RAM/ROM data/address bus and all was fine.But I went to check the clock signal of the Z80 it was stuck high:

Z80_clock_probing

The clock is generated by a 28MHz oscillator then divided by a 74F163 and inverted by a 74LS04 before reaching pin 6 of Z80 with a frequency of 3.5 MHz:

sound_system

On this kind of Toaplan hardware the Z80 commands not only the sound system but also the I/O, this would explain why the whole system didn’t get initalized since the 68000 could not find the Z80 running.Confident I went to remove the 28MHz oscillator :

DSCN3871

Fitted a good one and :

DSCN3872

Board risen from its grave!Mission accomplished.

 Posted by at 1:05 pm
Jul 162016
 

Got this orginal Hellfire PCB (by Toaplan) for a repair:

DSCN3844

After some initial problem due dirty sockets of program ROMs and oxidized JAMMA edge connector which caused missing boots, I was greeted by this scenario:

Sprites were wrong, garbled and stretched all over the screen.This part of graphics is generated by the custom ASIC ‘FCU’ :

FCU_ASIC

I did a reflow of it but this didn’t lead to any improvement.Probing around I found a 6116 SRAM with some data lines stuck low:

DSCN3847

Chip failed once tested out-of-circuit:

6116@2W_failed

But still no big improvements.Testing TTLs with my logic comparator I found a 74ALS169 counter @3N with bad outputs:

DSCN3849

Its output pin 15 was almost shorted to VCC (only 7.9 Ohm measured)

DSCN3850

Once removed, the chip failed miserably :

74ALS169@3N_reworking

 

Finally the sprites were correctly drawn but blocky :

DSCN3853

I noticed that, if I pressed down the ROM 9 @4E, sprites were 100% restored:

DSCN3856

Removing the EPROM revealed oxidation on socket pins:

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So I replaced it:

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Installing a new socket fixed game completely.

 Posted by at 6:28 pm
Jul 122016
 

Had this original Double Dragon II – The Revenge in my faulty boards pile so I deciced to take a look it hoping to fix it and complete the trilogy in my collection:

DSCN3795

Once powered it up I was greeted by this static garbage screen:DSCN3797

A static screen is a clear sign of some trouble in the main code execution.So, for first, I went to dump the program ROMs and found a bad device which game me different checksum at each reading.Since my ROM set was an undumped japanese one, I was forced to convert my board into the US set which is available.This did not lead to any improvement so further investigation was needed.When I removed the EPROMs, I noticed that the socket @IC63 (the one of the bad EPROM) was oxidized:

DSCN3798

I decided to replace it.When , before installing the new one, I was checking all the connections, I found an eaten trace underneath which should have tied pin 2 of the 74LS138 @IC64 (which generates the /CE signals for program ROMs) to pin 9 of a 74LS273 @IC71:

broken_trace_IC63_

Once restored the connection board finally booted up but with severe sprites issues and corrupted/missing sound FXs:

Probing RAMs on video board I found some data lines stuck low on a TMM2015 @IC83 :

DSCN3816

This was due two broken traces on solderside which I promptly patched:

broken_trace_IC83

This improved a little the issue giving back the missing lines to sprites but they were still wrong and garbled.Looking at MAME source, I could figured out that one of the two Z80 (the one @IC50) on top board is used as sprites CPU which takes data from a 27512 EPROM @IC37 and write/read them on a 6116 SRAM @IC24 :

srpites_CPU_circuitry

Probing this static RAM (actually a Sanyo LC3517BSL compatible with 6116) revealed weak signals on its address bus:

DSCN3819

Once removed the chip, it failed when tested out-of-circuit:

TMM2015@IC24_reworking

With a good RAM chip all the sprites were correctly restored :

sprites_restored

So I moved to troubleshoot the sound FXs issue.Samples are played by an OKI MSM6295 @IC74 with takes data from two 28 pin 1Mbit MASK ROMs @IC39 and IC40:

ADPCM_circuitry

Probing the two MASK ROMs revealed that data came out when requested so the problem had to be in the OKI MSM6295 chip which played them badly.I removed it :

DSCN3831

and put back a good one:

RSCN3833 This restored ADPCM samples.Board 100% fixed and board trilogy complete!

 Posted by at 7:21 pm  Tagged with: