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Fixing a Mortal Kombat 2 Pcb

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myPinballs View Drop Down
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    Posted: 06 Aug 2017 at 9:07pm
So i'm starting another repair, after fixing the TMHT pcb. This time a midway Mortal Kombat 2 pcb. These boards are going to be additional games i can play when i find an original r-type cabinet and board :)

So this board was part of a few pcbs i picked up with week. The others were capcom cps era.

This board appears to be dead. I've been messing about with it on and off over the last few days. This is what i get when powering on



Then after a few seconds the screen goes blank and i never get to the handy cpu board test screen :( Bloomin annoying.

Board is in good condition. No corrosion or previous repairs afaict. 




Board is the later version, with the 8mb roms so no need for the memory expansion card. I have removed the sound card for now to. Checked the voltages and am sure i have a good solid 5v, ground and 12v coming in to the board. 

Burned a new set of revision game roms even thought he originals checksumed ok. No change.

Probed the clock lines. All ok.

Probed the voltage and reset monitor ic. Reset line goes high for a few seconds and then goes low and high and repeats over and over, which is in time with the second Board led (DS3). The issue seems to be the watchdog line never pulses. So i'm guessing something is causing a cpu or custom asic crash. If you add a pulse to the watchdog line then it doesn't reset but still does not boot. So i'm thinking the monitor ic is ok.

Anyone have any ideas what's needed to get to the cpu test screen? Judging by whats on the screen, the custom asic seems the be the main ic, as the cpu is shown on screen as a test item. I haven't found any issues with the revision game roms and they don't appear in the tests so they must be part of it. All address and data lines and enable lines are present and pulsing though.

I did think of a possible option, as there are 4 ram ics which are part of the cpu section, and 2 of them on this board are Fujitsu brand (from experience with konami i suspected these may be an issue) but they actually appear in the cpu test as 'scratch ram' tests so my logic says these can't stop the test screen appearing if they are tested after it displays.

Brain ache!!




Edited by myPinballs - 06 Aug 2017 at 9:08pm
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Joker CK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joker CK Quote  Post ReplyReply Direct Link To This Post Posted: 06 Aug 2017 at 9:23pm
It's not very scientific but have you tried bending and flexing the pcb a little with the power switched on? These Midway boards were a bit flimsy and it's quite easy to have developed cold solder joints, particularly on the surface mount chips and socketed plcc chips that aren't visible to the naked eye that can cause issues. I had an MK2 that wouldn't get to the cpu test screen until I did a bit of flexing and prodding of chips.It ended up being a poor contact on the graphics processor socket. After replacing the socket I was able to get the game to boot.

Can't hurt to try. Hope you manage to get somewhere with the repair.

Edited by Joker CK - 06 Aug 2017 at 9:24pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JinKazama Quote  Post ReplyReply Direct Link To This Post Posted: 06 Aug 2017 at 9:59pm
I have similar issues with my MK2.... when I press the square socketed chip close to the jamma edge, pretty firmly while powering on, it boots.... When I let go it will either reset, show faults at the test screen e.d.... need a fix for this....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joker CK Quote  Post ReplyReply Direct Link To This Post Posted: 06 Aug 2017 at 10:52pm
Originally posted by JinKazama JinKazama wrote:

I have similar issues with my MK2.... when I press the square socketed chip close to the jamma edge, pretty firmly while powering on, it boots.... When I let go it will either reset, show faults at the test screen e.d.... need a fix for this....


Try removing the chip from the socket, desolder the socket and replace it with a new one. There are a lot of through-hole pins to desolder though so patience is needed! If you have a desoldering gun with an electric vacuum pump that would make the job a lot easier.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JinKazama Quote  Post ReplyReply Direct Link To This Post Posted: 06 Aug 2017 at 10:59pm
Thanks Joker! I might just try that! Any idea where a new socket can be bought?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joker CK Quote  Post ReplyReply Direct Link To This Post Posted: 06 Aug 2017 at 11:09pm
Originally posted by JinKazama JinKazama wrote:

Thanks Joker! I might just try that! Any idea where a new socket can be bought?


I managed to pick a few up from a local electronics store but eBay is always a good place to find cheap parts. Just make sure you get the correct size socket with the right amount of pins.

Good luck.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote myPinballs Quote  Post ReplyReply Direct Link To This Post Posted: 07 Aug 2017 at 8:58am
Originally posted by JinKazama JinKazama wrote:

Thanks Joker! I might just try that! Any idea where a new socket can be bought?

I have those 84 pin PLCC sockets in stock if you need some. Let me know. Your issue sounds isolated to that one socket and is a fault that you can reproduce reliably so that's good. 


Edited by myPinballs - 07 Aug 2017 at 8:59am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote myPinballs Quote  Post ReplyReply Direct Link To This Post Posted: 07 Aug 2017 at 9:12am
Few more updates. 

My issue doesn't appear to be related to PLCC sockets. I have removed both the custom asic and cpu ic, reseated and checked with a logic probe each pin. I can't find and floating pins other than ones not connected as shown in the schematics. Pressing the ics and flexing the board makes no difference.

What i'd really like to do before possibly changing the sockets anyway is to swap the asic and processor ics to rule them out. Unfortunately i don't have any!

Looking at mame, the cpu test page displays having already tested the video and pallete ram and the cpu. My board stops almost instantly before it even generates the garbage ram screens. I kind of get the first one shown but its not synced correctly and moves up/down the screen. Then the watchdog timeout kicks in and the screen goes blank. 

So i'm wondering what order these first ics are tested. I'm guessing that the cpu would be first then the video ram? If a garbage screen is shown even for a split second does that mean the cpu is ok? Hmmmm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote myPinballs Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug 2017 at 11:12am
Hi,

Quick request. Can someone confirm to me what is written (label etc) on the 2 PAL chips for the board. These are at locations, UE8 and UF17. A picture would be handy to.

Also what happens if you remove the ic at UF17 and then boot. Does it still get to the cpu test screen? If not what happens?

Thanks in advance.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JinKazama Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug 2017 at 12:36pm
I'm interested in a socket! Is someone with mediocre solderskills able to change one? Big smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joker CK Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug 2017 at 2:43pm
UF17 tells the game if it's the 4mb version or the 8mb version.

The 4mb version is labelled A-17480

8mb version is labelled A-17748

Edited by Joker CK - 08 Aug 2017 at 2:56pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joker CK Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug 2017 at 2:44pm
Originally posted by Joker CK Joker CK wrote:

Originally posted by myPinballs myPinballs wrote:

Hi,

Quick request. Can someone confirm to me what is written (label etc) on the 2 PAL chips for the board. These are at locations, UE8 and UF17. A picture would be handy to.

Also what happens if you remove the ic at UF17 and then boot. Does it still get to the cpu test screen? If not what happens?

Thanks in advance.


The 8mb PAL chip at UF17 is labeled A-17748

UE8 is A-16217




Removing UF17 won't let the game get to the cpu screen, at least on my board.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote myPinballs Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug 2017 at 3:35pm
Originally posted by Joker CK Joker CK wrote:

UF17 tells the game if it's the 4mb version or the 8mb version.

The 4mb version is labelled A-17480

8mb version is labelled A-17748

Thanks for that. I have a scratched sticker on my UF17 that i thought said A-17748, and that does match my board which is the 8mb version. I wanted to check this as the manual i have says A-17480 for it so i was wondering if i had the correct chip installed, as the board has unknown history

So what does your board do without this chip plugged in, anything on screen at all?? watchdog timeout loop with flashing DS3 led? As on my board taking this chip out makes no difference. I may as well burn a new one just to rule it out, as i have the files thanks to the archive at jammarcade.net


Edited by myPinballs - 08 Aug 2017 at 3:39pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote myPinballs Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug 2017 at 3:37pm
I'm also going to burn a new UE8 (A-16217) as mine has no label at all. Cant even see a trace of it.. It does look like the correct ic type (TIPPAL20L8), but too many times before i've had boards with wrong chips in that aren't easily identifiable.

Got to wait til tomorrow for some ATF22V10 ics, but can do a new A-17748 on an ATF18V8 later


Edited by myPinballs - 08 Aug 2017 at 3:38pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joker CK Quote  Post ReplyReply Direct Link To This Post Posted: 08 Aug 2017 at 5:19pm
Originally posted by myPinballs myPinballs wrote:

Originally posted by Joker CK Joker CK wrote:

UF17 tells the game if it's the 4mb version or the 8mb version.

The 4mb version is labelled A-17480

8mb version is labelled A-17748


Thanks for that. I have a scratched sticker on my UF17 that i thought said A-17748, and that does match my board which is the 8mb version. I wanted to check this as the manual i have says A-17480 for it so i was wondering if i had the correct chip installed, as the board has unknown history

So what does your board do without this chip plugged in, anything on screen at all?? watchdog timeout loop with flashing DS3 led? As on my board taking this chip out makes no difference. I may as well burn a new one just to rule it out, as i have the files thanks to the archive at jammarcade.net



Just realised that the board I tested with the missing UF17 was my non-booter and not my working board so no wonder I had no cpu screen! Whoops! I'll check my working board when I get the chance later.

Just a suggestion but have you checked the blank_x signal at UA4 and UD6? I know of boards that were missing video signal due to these chips failing. Worth checking as I find that it's often easier when someone else has had a similar issue to check their solution 1st as it could save you a lot of time.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote myPinballs Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2017 at 1:08pm
Originally posted by Joker CK Joker CK wrote:


Just a suggestion but have you checked the blank_x signal at UA4 and UD6? I know of boards that were missing video signal due to these chips failing. Worth checking as I find that it's often easier when someone else has had a similar issue to check their solution 1st as it could save you a lot of time.

Yeah i checked those and that is all ok, which i suspected would be the case as i do get a picture to begin with before the reset line kicks in.

Would you be able to take a quick pic of the scratch ram ics (UJ4,UJ5,UJ6,UJ7) you have on both your working and non working board. My board has 2 fujitsu rams at locations UJ6 & UJ7 and am back to thinking these could be a culprit. Other info i've received mention these rams can stop a board booting before the cpu test screen displays and we all know how crappy fujitsu ics are after 20+ years...


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joker CK Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2017 at 6:38pm


This is my non booting board. I've already changed 2 of the ram chips but still have issues so will be replacing the others too soon.

My working board is in my cab at the minute and is a bit difficult to get to currently. As soon as I can get to it I'll upload those pictures too.

Edited by Joker CK - 10 Aug 2017 at 6:38pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote myPinballs Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2017 at 6:49pm
Thanks for that. What does your non booting board do? Anything on screen at all? It will be interesting to see if your working one has any fujitsu rams on there or not.

Mine looks like this. (I removed the battery backup holder lost night to to check under it for any corrosion bust traces, no luck :(, or was that lucky!))



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Joker CK Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2017 at 7:58pm


This is my working board.

The non booter was coming up with Rom errors even though all roms checked good in another board and when verified with mame. I've had it stored away for a while and when i tested it recently I was getting the same symptoms as you. Probably something else failed in the meantime. I'm in the process of sorting out a proper test rig so plan to get back to fixing my board as soon as that's done.

Just looking at your picture, the ram in uj4 and uj5 seem to have different part numbers than mine? Are they the correct chips or suitable alternatives?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote myPinballs Quote  Post ReplyReply Direct Link To This Post Posted: 11 Aug 2017 at 6:18pm
Originally posted by Joker CK Joker CK wrote:


Just looking at your picture, the ram in uj4 and uj5 seem to have different part numbers than mine? Are they the correct chips or suitable alternatives?


Yeah thats just another part number for 256k 4-bit dynamic ram

So, i removed my 2 fujitsu rams from the board in an experiment to see what happens without them.



And the answer is the board does exactly the same thing without 1 or both of these rams installed. Hmmmmm. So i'm trying to determine if this helps understand things or not. I'm guessing that what ever is bust either isn't accessing the rams or the rams themselves are bad. I've got some new rams on the way to check so if this does fix it i'm going to be well happy.


Edited by myPinballs - 14 Aug 2017 at 10:09am
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