PCB Repair Logs – Page 4

Operation Wolf repair log #1

General, PCB Repair Logs, Repair Logs 6 Responses »

Mar 262020

I recently got two Operation Wolf boards from Muddymusic to fix.
This board was not booting at all and I got a screen full of flickering garbage

I removed all four of the 27C512 program EPROM’s and verified they were good. All of them matched the “World, Set 1” version in MAME.

I confirmed continuity between all the address, data and control pins of both EPROM’s and RAM was present and correct and it was so I opted to remove the two TMM2063 work RAM chips and test those

As you can see both failed. I replaced them and tested but there was no change.
Next I started looking at the reset circuit.

Here is the main reset circuit taken from the schematics

Using the logic probe I found that signal “/TMCL” (timer clear) was floating. Shifting focus to grid A5 on the schematics we see that this signal comes from pin 13 on the 74LS138 at location IC60.

Further probing found that the A18 signal on pin 2 was also dead. This signal is the buffered MA18 (address bus pin 18) and comes from the 74LS244 at location 65. Checking the signal on the LS244 revealed that it was present so there was a break in the trace some where.
I couldn’t see anything obvious so I patched it with some Kynar wire

No on boot up I get no more resetting buyt the screen is full of garbage still

Next I started looking at the custom PC080 tilemap generators, more specifically the RAM connected to it

Checking both of these with the probe showed me there was no activity on most of these pins and some others were stuck high

I removed both of them and checked them, obviously both failed

Replacing both of these now gives me something to see.
In test mode I get this

I looked into this fault for a good hour or so before I decided the RAM I fitted was too slow. Swapping for a faster RAM type fixed both of these issues.

Now the board would successfully pass the self test in the test mode I could see that I had an issue with colours.

I started off probing the colour RAM at locations IC64 & IC65 and quickly found bit 4 of the address pins stuck low

Using the schematics I could easily trace this back to a 74LS157 at IC52

Replacing this gave me my colours back

Now onto the sound board.
The good news is all the music was present and correct. The bad new was all the voice samples were not.

Again, using the schematics I see that ultimately the addressing for the Maskrom at IC21 gets set by a bunch of 4-bit counters at IC27-IC30.
Probing these I found that the UP counter wasn’t pulsing at all

Checking the 74LS04 at IC32 revealed this inverter was bad so I replaced it and sound was restored but the sounds just carried on playing one after the other (never got a video of this).
The Z80 sets the start and stop data by writing values to address $C002 & $C003 respectively which gets latched by a couple of 74ALS574’s and fed into the B side of a 74LS688 comparator

Using the MAME debugger I could see that the data being written to the 74LS574’s was correct but probing the /A=B output pin 19 of the comparators showed that these were either never matching or they weren’t working.
I couldnt find issues up stream of these so I desoldered them and replaced them with pulls from another board as I don’t have any spares.

I now have working sounds and fully working board set ready to return.

Dangun Feveron repair log #2

General, PCB Repair Logs, Repair Logs 4 Responses »

Mar 262020

I had this Fever SOS (international version of Dangun Feveron) PCB since many Years. Here is a picture of the board with the two chips I had to replace highlighted in red:

It had flickering sprites (the problem being pretty hard to photograph, I’m not able to show screenshots of it). In other terms, every second frame of sprites was not displaying.

1) The sprites are generated by a large 240pin custom chip labeled 9838EX002 – 013 on this board. Closer inspection revealed a cross marked on it by a previous repairer as well as a mark on pin #226. That pin goes to the RAS (Row Address Strobe) pin (#14) of a DRAM (424260) at U36, which is one of the two DRAMs that deals with sprites, each of them displaying alternatively one frame after the other.

There was no signal at all on that pin (#14). Probing the equivalent pin on the adjacent DRAM at U35 showed a pulsing signal. RAS being a signal going towards the DRAM meant that the large custom chip wasn’t giving the signal needed at pin #226.

I needed to change that large custom chip. These being on Cave 68000 systems, they are unfortunately available mainly on rare and expensive games (list available in the Cave 68000 MAME driver). After a long time, I finally had the opportunity to grab a UO Poko board which has the same chip, even labeled not exactly similar: 9749EX004 – 013.

Left is the faulty chip taken off the Fever SOS board. Right is a working chip taken off a UO Poko board. Notice how the left one blistered after heating it for desoldering, while the right one didn’t change.

2) Unfortunately, swapping the chip did not resolved my sprite flickering issue but at least the signal at pin #226 was then looking good. Probing the linked DRAM at U36 showed some weird looking signals on a few I/O pins (#2, 3, 4 & 5 pins).

I swapped it with a functioning DRAM (a NEC 424260). That finally resolved the flickering sprites problem.

Board fixed !

Lightning Fighters repair log #4

PCB Repair Logs, Repair Logs Comments Off

Mar 242020

I got a Lightning Fighters PCB with GFX problems. As you can see, major colors and layers issues:

1) Probing the Konami 053251 custom chip revealed some weak signals on a few pins. This chip is a priority encoder, it deals with colors and layers and seems to be prone to failure in more and more boards of that generation. Unfortunately, you have to find a donor board of the same era to get a working one (good thing anyway is that it is used in a pretty good amount of Konami games).

Here is the result after swapping it with a good one:

2 & 3) Colors and layers are now fixed but we have some jailbars on sprites. This looks to be a sprite’s data issue. Probing the mask ROMs revealed missing signals on a few data lines for 939A05 and 939A06 ROMs. I replaced them with two burnt 27C400 EPROMs. Board is now fixed:

Here is an overview of the chips I had to replace on the board:

Double Dragon II – The Revenge repair log #2

PCB Repair Logs Comments Off

Jan 252020

This board is a bootleg board but seems to follow the original fairly accurately.

On initial boot up this didn’t do a great deal but then other times it actually started up with various errors.

A fault like this always makes me look at the reset circuit.
This board uses a 6809 as the main CPU and a Z80 as a sub CPU.
The reset pin for the 6809 is pin 37 and using the scope I could see that most of the time it didn’t do what a reset should do.
Tracing it all back I came to this

The reset circuit on this is as simple as it gets really with a capacitor, resistor and diode.
I removed and replaced the capacitor and now the game boots up every time.

Now, although the game booted it appeared to crash when entering attract mode or starting a game with this fault

I remembered Bryan McPhail had the very same issue some time ago and he mentions that the sub CPU needed to be running.
Checking the ROM for the sub CPU I found pin 1 (A15) was dead. Further inspection of the solder side of the PCB I found this

I patched this up as neat as I could and covered it using an overcoat pen

Now the issue was fixed

Last thing to do was deal with the sound.
My initial inspection of the PCB showed the volume pot had been messed with

I removed it and found some bad track damage underneath and on top

I fitted a new pot and patched all this up nicely but I still had no sound.
Tracing it out revealed that the bootleggers mixed up the two SPEAKER connections so SPEAKER+ was connected to SPEAKER- on the JAMMA edge and vice versa.
I spoke to Muddymusic to see what he wanted me to do. The option were hack the board to swap them or make an adapter. The prior option was chosen and I cut the two traces and ended up with this solution.

Now everything works great

Pacland repair log #3

PCB Repair Logs 2 Responses »

Jan 012020

Next up in the box of brokenness is a Pacland.

Visual inspection revealed the amp had blown up

I also saw the usual corrosion on the legs of some of the customs

and the socket didn’t look too great either

As you would expect there were some pins missing from the chip when I removed it

I soldered legs on best I could and opted to fire the board up.

This is a good start and using the error code list compiled by my good friend cmonkey I knew that this was a RAM fault.
Checking RAM 9N I found several address lines were dead

Using the schematics I could see those address lines came from a 74LS32 @ 10J

I confirmed the outputs were bad and replaced the chip.
Now I get this when booting

Game is booting but some scroll issues and some jailbars too.
I could affect the scroll issues by pressing on that custom chip I resoldered at the start. I removed it again and attempted to further clean the legs but I just made it all worse. In the end I opted to solder it into a socket.
It looks crappy but it got the job done

Scroll issues fixed I now turned to those jailbars.
This ended up being an easy fix. I removed the ROM at 6T and checked it in my programmer. Bit 5 was stuck high so I replaced the ROM which fixed the jailbars.

Last thing to deal with was the sound. Obviously I wasn’t going to get far without an amp and I don’t have any spares. Lucky for me, my friend Smarty sent me a replacement gratis which fixed the sound and completed the repair.

Thanks very much to Smarty for the amp.

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