Star Wars - board trouble - Help needed

SaminVA

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I am trying to get my second spare Star Wars board working and I could use some help. I had another thread started when I was working on my main board and in the process I was trying to use this board set for testing. This board started out completely dead but replacing the CPU and some of the RAM chips I got the board working but it still has problems. I know the AVG vector board works 100 % as it was tested on my working board set. It still has my original graphics glitch because the AVG chip is bad but it will get a new chip when I get the problem with the main board figured out. I also have a sound board problem, it too was totally dead but came back to life with a new CPU ,RAM and PIA chip. I now have sound and music but have no speech. I'll get back to that after the main board problem is fixed. Now for the main board problem. In game mode the attract mode runs but theirs no stars in the background. You can coin up a game but no stars and no tie fighters or death stars, nothing. You can only shoot endlessly into the black of space. As I said before I do have music and sound effects but no speech. In the video I have the sound board removed so I can have access to the main board. In test mode it's reporting a Bad Math RAM at 5H. I know the RAM is good, it's been swapped and tested in the other board. If I swap the RAM at 5H with 5F it still reports 5H as Bad. I am also getting Matrix Errors but I believe it's because something is keeping the RAM at 5H from working. I have searched this board as well as the Vector List and Google and found some problems close to the same and one almost identical but it was a 5F error instead of 5H but no solution was ever posted.
Here's what I know so far, all ROMs and Rams and PROMs are tested good, that includes the 4 PROMS at 7H,7J,7K and 7L. I have also replaced the socket and replaced the 74LS245 at 4H which is the Matrix Processor Data Selector with no change. Comparing the 2 RAMs at 5H and 5F as well as the 74LS245s at 4H and 4F with a logic probe the only difference is pin 10 on the RAM 5H and pin 8 on 4H are stuck low wile pin 10 on the RAM 5F and pin 8 on 4F are pulsing. This is as far as I have checked and I was wondering if anyone has any suggestions of what to check next. I have been looking over the troubleshooting guide but haven't figured out what you do even if you set the dip switches and perform a test I don't understand what is suppose to happen? Someone needs to write a Star Wars troubleshooting guide for dummies.


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Take a good look at the underside of the board, check all the traces for breaks. I have fixed lots of SW sets and found lots of breaks where the boards have been stored on top of other boards. Also look under the RAM, I've seen breaks caused by people using screwdrivers to remove the IC.
The diagnostic setup procedure is listed in the manual....It's a little confusing at first but once you figure out that what is displayed is the expected result followed by the actual result you get an idea which section the problem is in.

Check 5E 74ls08 is good. pins 1 ,2 and 3.....1 and 2 being the input and 3 the output.
 
Take a good look at the underside of the board, check all the traces for breaks. I have fixed lots of SW sets and found lots of breaks where the boards have been stored on top of other boards. Also look under the RAM, I've seen breaks caused by people using screwdrivers to remove the IC.
The diagnostic setup procedure is listed in the manual....It's a little confusing at first but once you figure out that what is displayed is the expected result followed by the actual result you get an idea which section the problem is in.

Check 5E 74ls08 is good. pins 1 ,2 and 3.....1 and 2 being the input and 3 the output.

Thanks omegaman for the suggestion. I got out my logic probe and tested the 74LS08 at 5E but I am still not sure if the chip is bad. I made a video first testing each pin on the bad board and then on my good board. I figured someone that has more experience with a logic probe might be able to tell if their's a problem with this chip and if not where to check next. I could install a socket and new chip but right now I only have a 7408 not a 74LS08 and I am not sure if that would work. I did place an order so I will have a 74LS08 in a couple days. Till then I plain to look the board over good with magnifier glasses to see if I have any cut traces on the board. If anyone has any thoughts or suggestions I sure would appreciate them.
 
On Ram 5H pin 10 (MDB1) if the 245 at 4H is good and the RAM is known good then it could be another chip that has MDB1 going to it. It looks like it runs to 7D (74ls299) pin 4 so that could be dragging it down....I only have poor pdf schematics to look at here, will try to dig out the paper ones later and take a good look.
 
Not sure if this will help, but here goes :) .

My SW board also developed this problem with similar matrix errors listed awhile back. I tried to fix it myself (and my basic board/oscilloscope skills) to no avail...replaced a few chips that seemed to possibly not be doing what they were supposed to be doing based on the schematics and what I was seeing on the scope, but again, no dice.

I ended up sending it to Alex Yeckley who fixed it. He said it was a bit of a bear to trace it down, but it ended up being chip 7A (a 74LS165) in the "Register" section of the main board (Register A). He didn't specify what the chip was failing to do, but this chip was the culprit.

So maybe the above can provide you with a clue as to where to look.

Good luck!

Jon
 
Thanks guy's for the help.
Yes, my troubleshooting skills are lacking also but I want to learn so theirs nothing like hands on experience. I have found out a little common sense and the process of elimination sometimes will work along with a little help from friends.
I know their's a problem with the RAM at 5H, pin 10 is stuck low. The RAM itself tests good. It's always low even when you toggle resett.Pin 10 of 5H is marked as MDB1 and is an I/O input output of the RAM so I guess that is a Data Bus or line? Either way it should not be low, it should be pulsing like on my good board. Pin 10 connects directly with pin 8 of 4H 74LS245 which is also marked MDB1 and is also low. I have also installed a socket and put a new chip in so I know it's also good. I looked at the schematics and found every IC with a pin marked MDB1 which I listed below and they all are stuck low so I am trying to figure out what chip dose what and which is most likely to be causing the problem.
Jon the one that caused your problem 7A 74LS165 which is Register A is suspect because Pin 5 is listed as MDB1 and is stuck Low. So are the rest.
5H (6116 Ram) pin10 - MDB1 - Low RAM good
4H (74LS245) Matrix Processor Data Selector pin 8 - MDB1 - Low ,Chip replaced
7D (74LS299) Accumulator pin 4 - MDB1 - Low
7C (74LS384) Serial Multiplier pin4 - MDB1 - Low
7A (74LS165) Register A pin 5 - MDB1 - Low
7B (74LS165) Register B pin 5 - MDB1 - Low
It could be one of these chips but it could also be any chip also connected to any one of them. If I could determine the path of the signal MDB1 that's between these chips it should get me closer to where the problem would be. I hate to just start swapping chips without some thought as to which would be the most likely at fault.
I also stumbled on what might be another problem. It seems I am missing the 3 MHz clock signal on several of the chips so I am going to check out all the clock signals and see which are their and which are not.
I'll report back with my findings.
 
Looks like you are getting closer now. Yes the best way to learn anything is to make a few mistakes along the way.
My money would be on one of the 74165's, you could try and cut the leg neatly so that you could solder it back together again.......or if your de-soldering skills are good, remove them one by one and solder back in rather than fit a socket....you really need an IC tester though.
If you have an accurate or low ohms meter you could measure the value between the stuck pin on each chip listed and ground or +5V.....see which one has the lowest reading.
 
I think I have read every post about Star Wars board repair problems. So much to take in its all jumbling up in my head where it feels like it might explode.
I did read something that got me thinking, both in the troubleshooting guide and in other repair posts.
It said to check all your clock signals first so wile poking around with my logic probe I found some of my 3mhz clocks either stuck Hi or Low. Is this normal? Shouldn't all clocks be pulsing,maybe pulsing Hi or Low or Hi and Low together?
Here's a list of the chips and pins I found with a stuck 3mhz clock
Divider Control
8N 74LS00 - pin 1 - R/WB Low Hi Pulse
pin 2 - 3 mhz Pulse Low Hi
pin 3 - Hi Low Pulse
pin 9 - 3 mhz stuck Hi

3M 74LS00 - pin 13 - 3 mhz stuck LOW

Difference Latch
6R 74LS74 - pin 11 3 mhz stuck Low
4M 74LS374 - pin 1 OC 3mhz Stuck Hi
pin 11 CK 3mhz Stuck Low
5M 74LS374 - pin 1 OC 3mhz Stuck Hi
pin 11 CK 3mhz Stuck Low

Quotient Shift Register
5J 74LS164 - pin 8 CK 3mhz Stuck Hi
5K 74LS164 - pin 8 CK 3mhz Stuck Hi

Divider Clock Generator
8R 74LS191 - pin 14 CK 3mhz Stuck Hi
8P 74LS109 - pin 4 CK Stuck Hi not sure of clock feq here, runs to pin 13 of 8R marked as RIP
pin 9 Q 3mhz Stuck Hi
pin 10 Q 3mhz Low
pin 12 CK 6mhz Pulse Low
Dividend Shift Register
3N 74LS299 - pin 3 G2 3mhz Stuck Low
7M 74LS299 - pin 3 G2 3mhz Stuck Low

All other clock signals 12mhz,6mhz,3mhz and 1.5mhz seem to be Ok or pulsing.
So could this be one of my problems or just a symptom of another problem.
I realize I could have more than one problem going on at the same time.
I'll keep digging.
 
I would check 5c and 5d ls164 pin 8 for a signal. This is a random nuber generator and may be used to determin when the enemy ships are supposed to appear. Again I am new to the arcade stuff but there should be a clock signal on pin 8 of them chips.
 
I would check 5c and 5d ls164 pin 8 for a signal. This is a random nuber generator and may be used to determin when the enemy ships are supposed to appear. Again I am new to the arcade stuff but there should be a clock signal on pin 8 of them chips.

Thanks for the suggestion but that's why their not on the list. Pin 8 of both 5C and 5D have the 3mhz Hi Low Pulse clock signal as well as pin 12 of 4D which all 3 make up the Pseudo-Random Number Generator.
Keep the suggestions coming.
Thanks
 
Sam,
I would locate the problem with MDB1 being stuck first, you will most likely find once that is sorted the correct signal will start the Divider clock generator.
Looks like you have the 4 IC's to check.
7A
7B
7C
7D
 
Sam,
I would locate the problem with MDB1 being stuck first, you will most likely find once that is sorted the correct signal will start the Divider clock generator.
Looks like you have the 4 IC's to check.
7A
7B
7C
7D

omegaman, I believe you are right about locating the problem with MDB1 first so I decided to do some more testing. First I made sure I found every IC that had MDB1 listed and then I followed each trace from the pins to make sure I had found every one of the MDB1 lines. Sure enough their were a total of 6 IC's , 2 of which have been ruled out and the pins were all connected together with board traces and all the MDB1 pins tested Low with the logic probe. I knew that meant 0 voltage or maybe even a short to ground. I remember seeing or reading somewhere about finding a shout in an IC with an OHM meter so I took a reading and sure enough I had a short to ground on every one of the MDB1 pins but not a dead short but almost. I measured the resistance at each pin and this is what I got.
5H (6116 Ram) pin10 - MDB1 - Low RAM good 2.9 OHMs
4H (74LS245) Matrix Processor Data Selector pin 8 - MDB1 - Low ,Chip replaced 2.9 OHMs
7D (74LS299) Accumulator pin 4 - MDB1 - Low 2.6 OHMs
7C (74LS384) Serial Multiplier pin4 - MDB1 - Low 2.7 OHMs
7A (74LS165) Register A pin 5 - MDB1 - Low 2.9 OHMs
7B (74LS165) Register B pin 5 - MDB1 - Low 2.9 OHMs
The only way to tell where the short is would be to remove the IC or at least cut the shorted pin but already knew 5H and 4H were not the problem so that left 4 ICs so I decided to just replace them. I had quite a few 74LS ICs on hand but not the ones I needed so I made a list and had to order from 3 different places to get all the values I needed. So far I have only received one order which was off Ebay of all places and it was for the 74LS165 which happens to be 7A and 7B so I pulled both and replaced them with sockets. I did another check and I still have the short with 7A and 7B out of the socket so they were not the problem.
That left 7D (74LS299) and 7C (74LS384) I have the 74LS299 on the way but the 74LS384 seems to be hard to locate. In fact I noticed my board has a AM25LS14PAC installed at 7C which is a direct replacement for the 74LS384. So I was hoping the 74LS299 at 7D was the shorted IC and it did have the lowest resistance reading at 2.6 OHMs so I decided to pull it next. After pulling 7D 74LS299 I checked again for the short and it was now gone. I checked the 74LS299 between pin 4 MDB1 and pin 10 which is ground and I got 2.6 OHM reading which was my short. I feel sure this is my problem with the MDB1 data line but wont be able to try the board until my order with the 74LS299's arrive. I am hopeful this will be the fix. I will report back soon I hope. I placed the order with B & G Micro 7/20/11 and their website still lists my order as pending. If only Bob Roberts had the 74LS299, I would have ordered from him and had my order but he didnt have them listed.:(
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My Star Wars board #2 has come back from the dark side. :D
It turns out the 74LS299 at 7D which had a shorted data line at pin 4 was indeed the reason my game didn't have stars and ships and was causing the self test to report a bad RAM at 5H which was known to be good.. The game is now error free and only has the graphics glitch because I have the bad AVG chip installed that was in my other game. I now have swapped in the new AVG replacement I got from Arcade Shop so I can start troubleshooting the problem with the sound board. I'll just order a new AVG for the other board. The board has been running for a few hours now with no problems so it's time to start on the sound board. It was completely dead but replacing the CPU,SRAM and PIA IC's I now have music and sound but no speech, just some odd noises. I swapped the speech chip with the one from my working sound board with no difference so the problem must be else where. I have all the music and sounds so I am assuming all 4 of the pokey chips are good. I am leaning on one of the TL084's are bad. It looks like the TL084 is listed on the schematic but the board has LF347N installed. I assume these IC's are the same and interchangeable?
I think I will start another thread for the sound board so look for it soon. I should have some of my sound board IC's that I ordered on Monday. I still haven't got my order from BG Micro which I placed 7/20/11. That order had my 74LS299 chips which I got tired waiting on so I ordered some off Ebay 2 days ago and got them today which is how I got the main board up and running. I just hate to wait on parts.
I would like to thank everyone for the help, especially omegaman. Your suggestions were right on target.
Now off to that sound board.
I also have developed a problem with the control yoke. The up and down is fine but the right and left sometimes seems to not move and then jump around. It dose it with both boards so I am certain its a problem with the pot or the gears. I know the rubber bumpers are gone so I am sure it could use a rebuild kit. I'll have to pull it apart and see what's the damage. I suppose that could be another thread. :)

 
The force is strong in you young Sam !!!


:) well done, glad you got it running.


What do you hear on the speech? You can put the sound board into test mode with some jumpers. I will take a look at the drawings if you can give a detailed description of the problem.....video Clip would be perfect.

What an excellent and informative thread this turned out to be.
 
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The force is strong in you young Sam !!!


:) well done, glad you got it running.


What do you hear on the speech? You can put the sound board into test mode with some jumpers. I will take a look at the drawings if you can give a detailed description of the problem.....video Clip would be perfect.

What an excellent and informative thread this turned out to be.

Already in the works. I figured a video would show the problem best and I think I will start a new thread.
I have been reading up on the sound test and it doesn't look to hard. Looking over the schematics right now I suspect a problem with 4C TL084 which it's really a LF347N on the board. When I placed the order I didn't realize these were the same chip so I ordered both. I wonder which is the better of the two or if theirs any difference. Either way according to the UPS tracking the order should be here Monday but I should be able to do some testing before then.
 
This is great to hear...congrats on the fix! :)

And this thread is great as we now have a good description of what to do for other SW boards that develop these "matrix" issues!

Jon


My Star Wars board #2 has come back from the dark side. :D
It turns out the 74LS299 at 7D which had a shorted data line at pin 4 was indeed the reason my game didn't have stars and ships and was causing the self test to report a bad RAM at 5H which was known to be good.. The game is now error free and only has the graphics glitch because I have the bad AVG chip installed that was in my other game. I now have swapped in the new AVG replacement I got from Arcade Shop so I can start troubleshooting the problem with the sound board. I'll just order a new AVG for the other board. The board has been running for a few hours now with no problems so it's time to start on the sound board. It was completely dead but replacing the CPU,SRAM and PIA IC's I now have music and sound but no speech, just some odd noises. I swapped the speech chip with the one from my working sound board with no difference so the problem must be else where. I have all the music and sounds so I am assuming all 4 of the pokey chips are good. I am leaning on one of the TL084's are bad. It looks like the TL084 is listed on the schematic but the board has LF347N installed. I assume these IC's are the same and interchangeable?
I think I will start another thread for the sound board so look for it soon. I should have some of my sound board IC's that I ordered on Monday. I still haven't got my order from BG Micro which I placed 7/20/11. That order had my 74LS299 chips which I got tired waiting on so I ordered some off Ebay 2 days ago and got them today which is how I got the main board up and running. I just hate to wait on parts.
I would like to thank everyone for the help, especially omegaman. Your suggestions were right on target.
Now off to that sound board.
I also have developed a problem with the control yoke. The up and down is fine but the right and left sometimes seems to not move and then jump around. It dose it with both boards so I am certain its a problem with the pot or the gears. I know the rubber bumpers are gone so I am sure it could use a rebuild kit. I'll have to pull it apart and see what's the damage. I suppose that could be another thread. :)

 
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