Apr 062019
 

Got for repair from USA this faulty original Ghosts’n Goblins PCB, a two stack made of a CPU board :

And a VIDEO board:

Both boards were very dirty especially on solder side:

Some areas were corroded too:

Before applying power I washed both boards and neutralized the corrosion with some vinegar.On smoke test the game booted up, it was playable with sound too but with noticeable graphical issues :

I polished the contacts inside the connectors of the ribbon cables and the big vertical bars disappeared but backgrounds were kinda pixelated :

The circuit which generates the tiles lies on VIDEO board and it’s labeled as “SCROLL” in schematics (last three pages of PDF).Checking it with a logic probe I quickly found a 74LS273 @6A with a dead output:

The scope confirmed the output (pin 15) was floating while input (pin 14) was toggling:

The signal from this dead output is called ‘SVFLIP’ in snippets of above schematics and it’s routed to the inputs of a 74LS86 @5B which outputs some address lines for the backgounds ROMs:

Probing the 74LS86 @5B with my HP10529A logic comparator revealed troubles on output pin 3 and 6:

I removed it along with the 74LS273 @6A :

Both chips failed the out-of-circuit testing :

I installed sockets with good chips :

Backgounds were so restored and board 100% fixed.End of job.

 

 Posted by at 10:36 pm
Apr 042019
 

Received for repair from Germany a ‘1943 : Midway Kaisen’ PCB (same hardware of export version ‘1943 : The Battle of Midway’ but with japanese ROM set).

Set is made of a CPU board :

And a VIDEO board:

The board was faulty, it showed graphic errors and had no sound :

Specifically the graphic faults concerned the text (also called “characters”), the scrolling and the sprites.Let’s go in order.

 

  • The text/characters issue.

The text had wrong colors, here is how it looked like:

 

Whereas it should have been (snapshot from MAME)

Schematics in hand I started to check the revelant circuit with my logic probe and found a stuck signal on an address line of the BPROM @7F on CPU board:

This signal is labeled ‘CC3’ on schematics :

I traced it back to the input (pin 8) of two 74LS273 :

 

Signal was toggling on the one @5E but absent on 6E:

There was clearly a broken trace somewhere between pin 8 of the two 74s273 so I ran a jumper wire on solder side, this restored the correct text :

 

  • The scrolling issue.

The problem showed itself like some of the backgrounds (like clouds) were fixed  :

Looking at schematics there are on VIDEO board two separate circuits for horizontal and vertical scrolling.Checking them I found a 74LS273 @2H with stuck ouptuts :

I removed the chip and tested it out-of-circuit, it failed as expected:

I installed a good IC and scrolling came back to normal.

 

  • The sprite issue.

Most of objects were fine but some of them (like bullets) sometimes turned into squared blocks:

Sprites data are stored in eight 27256 OTP ROMs:

I read them and dumps turned out to be good but as further proof I swapped the devices one by one with a good set from another same board.When I swapped the one @10A labeled ‘BM06’ the issue disappeared so I programmed a blank 27256 EPROM.Sprites were fine now but there were still some little glitches affecting them :

The sprites line buffer is made of two identical circuits called “LINE BUFFER 1” and “LINE BUFFER 2” in the schematics.Two 2K  x8-bit static RAMs (TMM2018) are the main part of this circuit :

Probing around I found nothing of abnormal but I noticed that a 100pF ceramic capacitor was installed between pin 20 (/OE tied to GROUND) and pin 21 (/WE)  of one RAM whereas the other chip lacked of it (but I could see some solder residuals so perhaps the capacitor was present but then came off)

I installed the missing capacitor and this cleared the glitches,  sprites were perfectly displayed now.

Last issue to troubleshoot was the lack of audio.The 1K potentiometer was missing :

Fitting it did not restore the sound, the fault was in the digital part of the circuit made of a Z80 CPU, a 27256 ROM and a 2k x 8-bit SRAM (Toshiba TMM2015)

The ROM was dumped as good so I fired up my Fluke 9010A troubleshooter and launched a RAM test which reported an ‘R/W ERR @ C000 BTS 02’ of the TMM2015 @1K  :

This means the Fluke encountered an error at address 0xC000 (the start of the Z80 address space where the RAM lies) where it was unable to read/write ‘bit 02’ which turned from hex number to binary is ‘00000010’.Translated into hardware this means that data line ‘D1’ of the TMM2015 SRAM was not working hence chip was likely faulty:

I pulled the RAM:

Chip failed the out-of-circuit test :

Fitting a good RAM chip restored the sound and fixed the board completely.Job done.

 

 

 Posted by at 12:10 pm

Contra repair log #2

 PCB Repair Logs  Comments Off on Contra repair log #2
Mar 202019
 

Got from USA this original Contra (by Konami) PCB for repair :

Board simply booted to a black screen, time to investigate then.A closer inspection revealed the 3.58MHz oscillator was missing:

This provides clock for the YM2151 IC as you can see on schematics:

I fitted it but obviously board was still dead so I focused on the main CPU ( an HD63C09) dumping the two program ROMs:

Analyzing dumps revealed that somebody installed another sound ROM (like the one @12A) in the socket of the program ROM @18A, you can see in above picture that indeed there are two devices with same ‘633E01’ label.I programmed an empty 27256 EPROM but board was still not booting.Looking better at PCB I noticed the ‘007593’ palette custom IC @1F was damaged :

The package was really cracked isolating pin 24-28 from the rest of its internal circuit :

The custom ‘007593’ exchanges 8 bit of color data with main CPU and other devices through pin 21-28 as per schematics :

This did make sense so I promptly removed the custom and installed some 1.778mm headers:

As some of you may remember some time ago I made a reproduction of the ‘007593’ :

Konami ‘007593’ & ‘007327’ reproduction

So I assembled and installed a unit :

Board booted into game with no further issues.Repair accomplished.

 Posted by at 10:20 pm
Mar 182019
 

Received from Portugal a cocktail version PCB of Indiana Jones, a real “holy grail” given its rarity.The peculiarity is that it runs on a different hardware than usual Atari System 1.Board is a two stack one made of a ‘main’ PCB :

And a ‘cartridge’ PCB :

All I got when I powered it up was a flashing ‘NO CARTRIDGE’ message on screen, watchdog was active and board resetting in an endless loop:

I started my troubleshooting with some preliminary things like reseating chips and ribbon cables.This worked in some way because it shutted down the watchdog and put the board in a static red screen :

Despite this state I was able to enter into TEST mode and perform all checks that were successfully carried except for the sound test which failed reporting this error :

The sound CPU is a 6502 located on cartridge PCB:

I replaced it with a good one and board booted into game.All seemed to be working fine, game was full playable but in a comparison with MAME I found that speeches were missing on my board

Here is how it should play:

I went into TEST mode and launched again a sound test.Music chip (YM2151) and Effects chip (POKEY) were tested good whereas the Speech chip test was silent:

The Speech chip is a Texas Instruments TMS5520:

Most of pins were inactive so,having a spare I replaced it but with no luck.Looking at schematics the TMS5520 exchanges data with the SY6522A (VIA, Versatile Interface Adapter)

I could not see anything else involved in the fault so I ordered the part which came into mail after some time:

I installed it and speeches were restored, board 100% fixed.Repair accomplished.

 Posted by at 4:07 pm

Extermination repair log and ‘X2-003’ – ‘RO-012’ reproduction

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Mar 112019
 

Some time ago I bought a lot of original faulty boards, there was among them a Taito PCB which at first gance I could not identify:

I could not power it up because there was a dead short between GROUND and +5V :

So I dumped some ROMs and it turned out to be Extermination, a vertical shoot’em up game (that runs on “The New Zealand Story” hardware) released by Taito in 1987.Someone previously tried to troubleshoot the board and cut one terminal of a zener diode thinking it was shorted but this was for +12V line protection whereas there is another zener diode to protect +5V which was actually bad causing the short to GROUND:

Once replaced the zener diode and cleared the short I powered the board up and it booted into game but sound was missing and colors were wrong with a dominant blue :

A blueish image means the RED color is missing or has some troubles.This was confirmed by the logic probe, the signal was indeed stuck low :

I could trace the JAMMA edge connector pin of RED back to a SIL component marked ‘RO-012’, a typical R/2R resistor ladder used as RGB DAC (one for each color).A closer inspection revealed the part was mounted backwards:

 

Reinstalling it with right orientation restored the RED color but image was now purplish :

This meant the GREEN color had some troubles.I located the relevant ‘RO-012’ DAC near the sound amplifier and found that some pins were shorted by a solder bridge:

Removing the bridge finally restored the correct colors :

Now the lack of audio.From signs on solder side I noticed someone previously reworked the sound section replacing the amplifier (an Hitachi HA1388) and potentiometer (and perhaps also capacitors)

Checking the +12V  confirmed this voltage was present on board but not on amplifier when I put the black probe of my multimeter on the two GROUND pins of the HA1388 (pin 4 and 9).At the end it turned out that who replaced the amplifier and potentiometer managed to lose their GROUND connection likely ripping off the rivets from the holes (power pins are always harder to desolder due to presence of internal planes).I restored the connections in this way :

Sound was back again.Board 100% fixed and job done.Before archiving this repair I took the chance to see if some parts (simple ones, not digital ASICs) were worth to be reproduced.I chose the aforementioned ‘RO-012’:

And the ‘X2-003’ :

The first, as said above, is an R/2R resistor ladder acting as RGB DAC, the latter is a capacitors/resistors array used for inputs but, unlike all the others, comes in a DIP16 ceramic package hence quite fragile.Reproducing them was straightforward :

 Posted by at 8:53 pm