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Womble
15th March 2009, 08:02 PM
Another Womble ramble I am afraid...

Now that I have a vertical cab I need to assign it an identity artwork wise, and I have very fond memories of playing 1943 as a kid. There's something about the drone of the engines as you loop the loop that is just very 1980s-arcadey.

So I snapped up a faulty Capcom 1943 board listed on the ebay UK recently, cost more to ship than it cost to buy but still cheaper than a working board locally all up I think.

http://i40.photobucket.com/albums/e230/Womble76/DSC00577.jpg

http://i40.photobucket.com/albums/e230/Womble76/DSC00578.jpg

Buying borked boards is always risky as you never know how the board died, it might be fixable or it might be a total wreck. The seller of this board claimed it was a permanent fixture in his mates cabinet, and that they played it incessantly during the summer, but when powering up after a few months off all they got was a blue screen. They took the board to the other guys house and tried it in his cab and got the same deal. At this point they decided to sell it rather than fluff around with it, as they knew they wouldnt be able to do much with it - these guys deserve a medal for that way of thinking. Assuming the seller was telling the truth and that it died inside the cab, there should be no chance the board had been plugged in backwards, so I took the punt.

It turned out that getting a blue screen is a bit hit and miss and the blue screen is actually the background seascape rather than just a blank blue screen. Powering on and off gives you about 5 different screens of crap

1) Alpha-numeric crap - classic Z80 in distress.

http://i40.photobucket.com/albums/e230/Womble76/DSC00567.jpg

2) Blue seascape with or without music.

http://i40.photobucket.com/albums/e230/Womble76/DSC00569.jpg

3) Repeating pattern of large blocks of ocean wave graphics - assume its part of the tsunami.

4) Half a battle ship

http://i40.photobucket.com/albums/e230/Womble76/DSC00570.jpg

5) Black screen with fragment of plane and explosions dotted about
6) Black screen.

Oddly enough hitting the coinup button will often cycle through the above, and or stop the music.

Certain AA members will be glad to hear I have finally sorted out my playroom and my 100Mhz Dual Channel CRO now has a permanent place of honour, after having spent the last 9 months in a cupboard coz its about twice the size I thought it was when I was bidding for it.

Having dumped and verified the ROMs, (a doubely good 1st test as it reseats every Eprom too) I moved onto the second most likely culprit (after power), the RAM. This board has 3 types of RAM, across the two boards. As is fairly standard, 1 board houses the CPUs, game code ROMs, sound system, and clock generation chippery, the other is the Video board which handles the video generation, sprites and graphicsy stuff. As the music could play I was pretty sure I could rule out the sound system and the graphics fragments I could get looked nice and clean, that just left the main system RAM at 10D. Also as they were socketed I was able to test the two Z80 chips in my Galaxians board and prove they worked.

Normally I would just work using a logic probe, in this case the right pins on the SRAM were active, the chip was not in standby and the control lines were busy. Looking at the activity with the scope it showed the control lines (WR and OE) were active and healthy. The address lines were also nice and healthy - healthy as in the voltage levels were transitioning pretty cleanly from logic 0 to logic 1. However the data lines (i.e. the output) were a mess on half of the pins, a number of the pulses were more like spikes and barely reached half way between the two logic states.

http://i40.photobucket.com/albums/e230/Womble76/DSC00574.jpg

So - whipped the chip out..

http://i40.photobucket.com/albums/e230/Womble76/DSC00579.jpg

.. and fitted a couple of 14pin machined pin sockets side by side to take the 28 pin slim M8464 chip which is pin for pin compatible with the original TMM2063 (cheaper than buying 28 pin sockets).

http://i40.photobucket.com/albums/e230/Womble76/DSC00582.jpg

The original chip failed the RAM test on my eprom burner miserably, it detected that a number of pins were unwell before it even tried the write/read tests.

Slapped in the salvaged M8464 SRAM chip, powered up the board and it booted happily.

http://i40.photobucket.com/albums/e230/Womble76/DSCN4747.jpg

The only thing wrong was the sound, everything bar the chip tune was missing. I briefly heard the shot noises very very faintly but that stopped pretty quickly.

Back on the test bench and looking at the board there are two Y2203 sound generators, feeding two YM3014 DACs which feed into the amp section. Hooked up my audio probe to the output of both DACs, the one at 2B was happily pumping out the chip tune, the one at 2C was giving out silence. Probing the input signals to the DAC showed 2C was getting no inputs. Tracked back to the Y2033 and some inputs were active and others not. In the end it was simpler to desolder it, fit a 40 pin socket and drop in a spare YM2203. This brought back all the shot sounds and some of the background noises, but not the classic 1943 drone sound effect, or any of the explosion noises.

At this stage I don't know if either of the two YM2203 chips are in perfect health, the sound effects that are missing are too complicated to be generated by any of the TTL logic in the sound section I would assume so perhaps one of the YM2203s is only half well.

So I reckon that the seller's story checks out - the board could well have just died in its sleep, the YM2203 chip probably died here as I just heard its last gasps. Need to put some more time into the remaining sound issue, but have run out of weekend! It plays well tho, she's definitely a keeper.

Womble
16th March 2009, 08:37 PM
Well the other YM2203 chip was duff too, not overly surprising I guess, all the background noise vanished when the second one was removed from the board, fitted another 40 pin socket and moved my one good chip to the 1C position.

All the explosion sounds, the engine drone were back.

So the YM2203 operate as follows

1C - Level intro music, explosions, engine drone, basically any noises when a bullet hits

3C - Game background music, teletype sound (when mission is assigned,) and any noises made when a bullet is fired.

Trouble is I only had one 2203 chip on my scrap boards, anyone here got one they could spare for a fee? I can guarantee it a great home on a classic board, in a nice machined pin socket! :D

Also - anyone got any ideas as to what single event (based on sellers story) would wipe out both YM chips, and the main system RAM chip?

RaMpAgE
16th March 2009, 10:54 PM
another great write up there womble, I can't help you with the 2203 but my guess would be a power spike while the players had the sound cranked right up while playing:blink::)

Arcade King
17th March 2009, 07:16 AM
I'll have a 2203 somewhere around here :)

Womble
17th March 2009, 07:49 AM
Thanks for the offer AK, but Davefjedi has already come to the rescue. :)

Its annoying though, I have half a dozen other types of sound chip on my scrap boards, but only one 2203 on about twenty boards, about 4 would have had them on originally but they have already been robbed.

hamish_nz
17th March 2009, 08:03 AM
thanks for the great write up

always good reading

maxpower
17th March 2009, 08:19 AM
Great story and great job! Where can I get started on learning this?? I change caps & stuff but would like to learn this stuff too.

Max

Womble
17th March 2009, 09:36 AM
You pretty much just pick up a board and have a go. One thing you certainly need from day one is a logic probe. They go for about $25 at jaycar and let you see the logic state of the IC pins, then you need to hit google to find the datasheet for that chip to see if its doing what it should be doing.

The more tools you have the easier it gets to an extent, add a logic analyser and you can compare an onboard chip with a known good one. It basically compares the outputs of the onboard chip with the known good one and asks if the board chips outputs are doing what the good chips outputs are doing. An oscilloscope helps too I have recently found, but none of the tools are infallible. A lot of it is gut feeling and following your nose, its great fun sometimes, especially when you make progress, but other times its tedious work. You might find you love it, or loath it.

The other problem is spares, TTL ram chips can be bought at Jaycar (a few types anyway), but they are expensive ($2 versus about 20c from overseas), having a drawer full of scrap boards is very handy as you never have to look very far to find the chip you need. SRAM chips used on these boards have been out of production for twenty years or so and are usually only available on scrap boards or as new old stock - which is always overseas these days.

So just track down a board you want to fix, get a logic probe, find some scrap boards and just have a go.

I did write up a fairly lengthy guide to repairing stuff a while, back - will attach the link here if I can find it.

I find reparing boards very addictive, I reckon I have more fun fixing them than playing them. I was lucky in that I met a bloke through ebay who imports boards and on sells them, he doesnt participate on this forum (or the other one) but I think he does wander through every now and again. For the last year he provided me with boards that needed fixing on the basis of, fix it if you can, no hurry, no stress, no problem if you can't. So I got to play with a lot of boards that I didnt have to pay for, he in return got some valuable boards back working again and could sell them for 5 time what they were worth in their non-working state. A couple of boards died on the operating table, a number were beyond repair, but my success rate was probably about 70% which I am pretty happy with. He also gave me most of his scrap collection which was very handy. Plus a guy I met through another forum gave me two toasted Atari Hard Drivin board sets which are massive and peppered with useful chips.

Beware about buying bulk sets of boards on ebay that are listed as faulty, they are faulty and are great for spare chips, but they have almost certainly passed through the hands of a number of people who can fix such things and are likely to really be scrap, ie if they were repairable they would have been repaired already. You can get some bargains on single boards, any fault will put off a lot of buyers.

The problem with starting out in any hobby is at the start you have no tools, you dont want to spend money in case you get bored with it, but without the basics you have a much harder time.

eg - Eprom burner - allows you to check and replace eproms, but also test TTL chips and RAM chips.

Other working boards - for any boards I fix for myself where a non-TTL chip goes in I always use a socket, that board then becomes a test baord for that type of chip in the future, so my 1943 board now lets me test YM2203 chips coz the replacements are socketted. Very handy when it comes to CPUs, they are so complicated its impossible to really debug them with a scope or a logic probe - what you really need is another system to test them in. I have a Cobra Command board that does absolutely nothing, it uses a 6809e and a 6502 CPU, I have no idea if either are working properly, they have no missing pins and the signals look healthy on the scope on most pins. Even though I suspect the chip may be dead I cant be sure without a working one to compare with, and if I had a working chip I wouldnt bother with the scope, I would just swap the CPUs over and see what happene.d

Desolder station - invaluable but not cheap (mine was a cheapy at $299) , lets you neatly and safely remove chips from the board, helps you build up a stock of parts, and also lets you remove suspect chips for testing off the board. Before I had a desolder station I had to fight with each leg individually and often resort to cutting the pins off the chip and desoldering each one. That ruins the chip, so you cant even easily test it afterwards and then you need a new chip to put in. Time consuming, wasteful and not very enlightening. Getting a 68000 CPU to fall out of the board in mint condition is pretty cool.

Scope is useful as I found above but its not essential, the only board I have fixed using it is 1943 and I would have suspected the RAM chip anyway, all my previous fixes predate my scope. Some of my failures may have been easier with it, but I went back to my flaky Galaga board last night with the scope and it didnt really help, am slowly going over the board with my logic comparator but have a nasty feeling I will get to the end and all the chips will test OK. You will find that custom chips are the bane of your life when repairing boards, you cant test them (unless you have a working board), you cant get spares easily, and there is no info online about what the chip is or what it should be doing.

Dont let the above put you off, find a board, grab a logic probe and take the 1st step, once you get a feel for what is going on you just pick it up. Just don't use an expensive or rare board as your 1st attempt, folk on here are very helpful when you get stuck. I have only been doing this a year or so and have learnt heaps through the AA site.

Check out this link too -

http://www.aussiearcade.com/showthread.php?t=2131&page=2

.. again, dont be put off, a lot of ebay sellers selling faulty stuff say "must be an easy fix", faults are rarely easy, probably the easiest ones are no sound faults, but even those can be a pain in the arse.

maxpower
17th March 2009, 10:58 PM
You pretty much just pick up a board and have a go. One thing you certainly need from day one is a logic probe. They go for about $25 at jaycar and let you see the logic state of the IC pins, then you need to hit google to find the datasheet for that chip to see if its doing what it should be doing.

The more tools you have the easier it gets to an extent, add a logic analyser and you can compare an onboard chip with a known good one. It basically compares the outputs of the onboard chip with the known good one and asks if the board chips outputs are doing what the good chips outputs are doing. An oscilloscope helps too I have recently found, but none of the tools are infallible. A lot of it is gut feeling and following your nose, its great fun sometimes, especially when you make progress, but other times its tedious work. You might find you love it, or loath it.

The other problem is spares, TTL ram chips can be bought at Jaycar (a few types anyway), but they are expensive ($2 versus about 20c from overseas), having a drawer full of scrap boards is very handy as you never have to look very far to find the chip you need. SRAM chips used on these boards have been out of production for twenty years or so and are usually only available on scrap boards or as new old stock - which is always overseas these days.

So just track down a board you want to fix, get a logic probe, find some scrap boards and just have a go.

I did write up a fairly lengthy guide to repairing stuff a while, back - will attach the link here if I can find it.

I find reparing boards very addictive, I reckon I have more fun fixing them than playing them. I was lucky in that I met a bloke through ebay who imports boards and on sells them, he doesnt participate on this forum (or the other one) but I think he does wander through every now and again. For the last year he provided me with boards that needed fixing on the basis of, fix it if you can, no hurry, no stress, no problem if you can't. So I got to play with a lot of boards that I didnt have to pay for, he in return got some valuable boards back working again and could sell them for 5 time what they were worth in their non-working state. A couple of boards died on the operating table, a number were beyond repair, but my success rate was probably about 70% which I am pretty happy with. He also gave me most of his scrap collection which was very handy. Plus a guy I met through another forum gave me two toasted Atari Hard Drivin board sets which are massive and peppered with useful chips.

Beware about buying bulk sets of boards on ebay that are listed as faulty, they are faulty and are great for spare chips, but they have almost certainly passed through the hands of a number of people who can fix such things and are likely to really be scrap, ie if they were repairable they would have been repaired already. You can get some bargains on single boards, any fault will put off a lot of buyers.

The problem with starting out in any hobby is at the start you have no tools, you dont want to spend money in case you get bored with it, but without the basics you have a much harder time.

eg - Eprom burner - allows you to check and replace eproms, but also test TTL chips and RAM chips.

Other working boards - for any boards I fix for myself where a non-TTL chip goes in I always use a socket, that board then becomes a test baord for that type of chip in the future, so my 1943 board now lets me test YM2203 chips coz the replacements are socketted. Very handy when it comes to CPUs, they are so complicated its impossible to really debug them with a scope or a logic probe - what you really need is another system to test them in. I have a Cobra Command board that does absolutely nothing, it uses a 6809e and a 6502 CPU, I have no idea if either are working properly, they have no missing pins and the signals look healthy on the scope on most pins. Even though I suspect the chip may be dead I cant be sure without a working one to compare with, and if I had a working chip I wouldnt bother with the scope, I would just swap the CPUs over and see what happene.d

Desolder station - invaluable but not cheap (mine was a cheapy at $299) , lets you neatly and safely remove chips from the board, helps you build up a stock of parts, and also lets you remove suspect chips for testing off the board. Before I had a desolder station I had to fight with each leg individually and often resort to cutting the pins off the chip and desoldering each one. That ruins the chip, so you cant even easily test it afterwards and then you need a new chip to put in. Time consuming, wasteful and not very enlightening. Getting a 68000 CPU to fall out of the board in mint condition is pretty cool.

Scope is useful as I found above but its not essential, the only board I have fixed using it is 1943 and I would have suspected the RAM chip anyway, all my previous fixes predate my scope. Some of my failures may have been easier with it, but I went back to my flaky Galaga board last night with the scope and it didnt really help, am slowly going over the board with my logic comparator but have a nasty feeling I will get to the end and all the chips will test OK. You will find that custom chips are the bane of your life when repairing boards, you cant test them (unless you have a working board), you cant get spares easily, and there is no info online about what the chip is or what it should be doing.

Dont let the above put you off, find a board, grab a logic probe and take the 1st step, once you get a feel for what is going on you just pick it up. Just don't use an expensive or rare board as your 1st attempt, folk on here are very helpful when you get stuck. I have only been doing this a year or so and have learnt heaps through the AA site.

Check out this link too -

http://www.aussiearcade.com/showthread.php?t=2131&page=2

.. again, dont be put off, a lot of ebay sellers selling faulty stuff say "must be an easy fix", faults are rarely easy, probably the easiest ones are no sound faults, but even those can be a pain in the arse.

Thanks for this Womble. I have a Flying Shark PCB that's stuffed so might play with that when I know more.

arcadus
18th March 2009, 09:25 PM
The other problem is spares, TTL ram chips can be bought at Jaycar (a few types anyway), but they are expensive ($2 versus about 20c from overseas), having a drawer full of scrap boards is very handy as you never have to look very far to find the chip you need. SRAM chips used on these boards have been out of production for twenty years or so and are usually only available on scrap boards or as new old stock - which is always overseas these days.



Love these logs Womble:023:
Lack of all TTL will be problem in the future.
Hopefully someone will produce a little 14/16 pin PROM capable of emulating all TTL variations.:D

Womble
20th March 2009, 06:10 PM
Many thanks to Davefjedi for a working YM2203 chip, the board is back 100% now.

http://i40.photobucket.com/albums/e230/Womble76/DSCN4750.jpg

:D

Davefjedi
20th March 2009, 06:15 PM
WOW you even cleaned it:redface

Womble
20th March 2009, 06:19 PM
No I didn't, was like that when I found it. :)

NateDizzle
16th July 2011, 07:48 PM
LOOOOVVEEEEE THAT GAME! Matter of fact, I've got one of those boards in the 'too hard, figure out later section' of my desk with the exact same issue. Shall go have a look. Always love your work Womble :)