Defender video problem- pulsing vertical lines

gunsablazin

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ive got a later version CPU.
The game boots and plays, but the video has very faint vertical lines that are spaced out about a 1/4 inch apart that are pulsing.

Ive changed out a bunch of chips. I'll list all of what was done in a later post, but wanted to just ask if anyone has come accross this problem or could suggest anything to try.

I have the game on a test rig. The same rig that when a different CPU is hooked up the video is fine. So, i know the monitor is fine, wiring harness and connectors are all fine.

thanks in advance for any help/suggestions.

I understand there are many circuits that interract with eachother, but WHICH CHIP OR CIRCUIT most relate to this issue?
 
ive got a later version CPU.
The game boots and plays, but the video has very faint vertical lines that are spaced out about a 1/4 inch apart that are pulsing.

Ive changed out a bunch of chips. I'll list all of what was done in a later post, but wanted to just ask if anyone has come accross this problem or could suggest anything to try.

I have the game on a test rig. The same rig that when a different CPU is hooked up the video is fine. So, i know the monitor is fine, wiring harness and connectors are all fine.

thanks in advance for any help/suggestions.

I understand there are many circuits that interract with eachother, but WHICH CHIP OR CIRCUIT most relate to this issue?


Pictures would be helpful too. What does your RUG pattern look like on boot? Any error codes on the LEDS?
 
Thank you very much for the quick response. i'll try and take some pics asap. i'm not sure what to look for as far as the rug pattern. sometimes it boots with a rug pattern that stays on without a sweeping line and a RAM failure appears.

the second and fourth LED stays on. (oxox). i was thinking this might be a ram socket that is giving this reading. but maybe theyre related
 
Thank you very much for the quick response. i'll try and take some pics asap. i'm not sure what to look for as far as the rug pattern. sometimes it boots with a rug pattern that stays on without a sweeping line and a RAM failure appears.

the second and fourth LED stays on. (oxox). i was thinking this might be a ram socket that is giving this reading. but maybe theyre related

Have you tested the voltages? That should be step one. After that you can start to look at other things.
 
Do you mean test the voltages at each chip? Pin14? I'm using the 4116 now but am reading about the simple mod to the CPU to upgrade to the 4164. I'll do this and see if it fixes it. And post pics when I can . Thanks again
 
This usually indicates a "stuck" address line on the video address bus.

One way to test for this, is to take +5V to pin 23 of the video decoder chip 3G. This will simulate the player 2 video flip and test the 74166's (video display decoders).

If the line goes away, it is one of the 74166's. If it stays, there is another issue.

If it is on the video side, the POST RAM test will generally not find it.

ken
 
thanks for the help guys,,, having issues downloading pics... would probably be hard to see in in the pics anyway,,,its really faint. i'll keep trying to though.

,,, i cant even find any 74166? did you mean 74165?
cant wait to check this when i get home. I'll report back :)
 
Ok, here's what I've done.
I did the 4164 DRAM upgrade on the CPU. here's a link that describes it:

http://www.scoresaves.com/misc/JustSayNoTo4116.html

installed 24 new mc4564 ic's(used these since it was stated that these chips can be used along with others just the same as using 4164)

no help to the vertical lines that are faintly pulsing - not that i figured it would,,,
anyway, then since i couldn't find the chip that Yellowdog was referring to and especially since the chip at 3G doesn't even have 23 pins on it....

I searched through the THEORY OF OPERATION for Defender upright games and found that if I unsoldered one end of the jumper located just to the right of chip 5B (The end of the jumper which is connected to the pad higher on the board) and using a test lead I then grounded this point with one of the screw holes of the CPU board. At the same time that I grounded this connection I had a logic probe connected to pin 1 of chip 2M . The THEORY OF OPERATION describes this:

1. If you do not see a change from high to low level(on the logic probe), then the chip at 5B is defective.
2. If the level changes but there is no change in the output of the 2M Multiplexer chip, the Multiplexer is probably defective.(im guessing they mean the screen will invert so that 2nd player of a cocktail game can see the screen?)
3. If you only get output with the screen control in high or low, but not both staes, then the set of registers selected when the output pulsing stops is probably defective.

Now, HERE's WHAT ACTUALLY Happened,,,
FIRST, The screen looks like it inverted for a split second(like for a cocktail, but inverted also in a way that the writing on the screen was BACKWARDS???!!(similiar to when the vertical yoke wires are reversed??) that cant be good
SECONDLY it would immediately RESET to a rug pattern? Then briefly display Initial RAM error message,,,then in a minute or so it would go into attract mode.

I doubt that this is supposed to reset the game.....SO, please offer up any suggestions as where I should turn my attention.
change out 5B?, 2M?, or the set of registers selected as mentioned above? or the other set of registers? or all of the above.

Thanks as always,,,Im going to bed :-l zzzzzzzzzz
 
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Sorry, I forgot they messed up the chip grid on Defender. It is pin 23 of the Video Decoder 2 chip (3K). You just need to supply +5V to this pin to cause the screen to flip.

And you are right on Defender they used 74165s. Sorry I am so used to working on the later boards I tend to forget some of the quirks in the Defenders.

ken
 
Hey Ken,
i put +5 to pin 23 of 3K and the game shows the screen inverted, but garbled with a total blue background then immediately resets to rug pattern and sometimes then says initial test ok other times RAM failure( i do understand what you were saying about it the diagnostic not catching it because its past a certain point)
BUT WHAT"S CAUSING IT TO RESET?
i'll try and pm you - would love to send the pics of what im seeing that way. for some reason i get an error every time i try and post pics to an album in my profile...im not doing something right:-(
im about to change out the video registers 1o, 2o,3o,and 4o. (i changed out 1o so far and then tested it,,,i might be seeing things,,,but it seemed to make the lines a little less visible. thanks for your time, johnny
 
OK, here's where I'm at with this.
After changing a couple of chips out without success i all of a sudden now had a bigger problem than before. the game would lock up (4 leds lit) nothing else !!!
I had just replaced a chip (cant think which one right now) but replaced it with a "NEW" chip......only to have the game LOCK UP.
Tried another 'new chip' and thank GOD , now i'm back where I started. vertical lines pulsing while game plays normally.

NOW,,,,, watch this !!!

Im scratching my head where there used to be hair....thinking, wondering, cussing, and just about to give up...(at least for the night) when I grab my new oscilloscope probe and touched one of the legs of the crystal and WALLLOAHH !!!! NO PULSING VERTICAL LINES !!! :)

C'mon, your telling me I "FIXED" the problem by just touching this????

SO, i enjoyed the game working perfectly for an hour or so and cut it off. The next day I turned the game on and the lines , of course, are back.
I forget which circuit has the crystal in it, but would the timing be off a bit, or one of the resistors, caps???
 
Well, that sucks,, I've changed out the crystal and the lines are still there- hell, it actually seems worst. WTF?
 
The timing circuit in Defenders is one of the twitchiest beasts in the known universe. Nobody seems to know why it even works. What was probably happening was that the very slight capacitance of your scope probes was cleaning up one of the clock pulse signals. Try to locate a 10 pF capacitor and connect it across from ground to the same point you attached the probe and see if that clears it up. If not, then try connecting the cap from ground to each of the pins on the chip right next to the crystal (74LS04 IIRC). I have seen this "mod" on several boards and have had to do it twice to get boards stable. I am not entirely sure why it works although I have some suspicions.

ken
 
The timing circuit in Defenders is one of the twitchiest beasts in the known universe. Nobody seems to know why it even works. What was probably happening was that the very slight capacitance of your scope probes was cleaning up one of the clock pulse signals. Try to locate a 10 pF capacitor and connect it across from ground to the same point you attached the probe and see if that clears it up. If not, then try connecting the cap from ground to each of the pins on the chip right next to the crystal (74LS04 IIRC). I have seen this "mod" on several boards and have had to do it twice to get boards stable. I am not entirely sure why it works although I have some suspicions.

ken

was about to launch into a dissertation but ken beat me to it! :D
... xtals can have mechanical defects hence dodgy when touched, and also as ken said - also check each of the caps in the clock circuit for mechanical faults (if touchy). might also have a bad one.

dont forget we are talking about a 32 year old game! age is a factor in components, solder joints and the assembly thereof.
 
Alright I got the game finally working perfectly without the vertical lines in the video. in most cases where a 74ls04 is called for a 7404 can be used.......
Well, not in THIS case.

As soon as I put a 74ls04 in a socket ( the one right next to the crystal 7p I believe) it plays perfectly! Sorry I put you guys through this

Thanks again for all your help
 
Alright I got the game finally working perfectly without the vertical lines in the video. in most cases where a 74ls04 is called for a 7404 can be used.......
Well, not in THIS case.

As soon as I put a 74ls04 in a socket ( the one right next to the crystal 7p I believe) it plays perfectly! Sorry I put you guys through this

Thanks again for all your help

Is that backwards? Defender uses a lot of 7404's and they cannot be replaced with a 74LS04 due to timing differences.
 
Yes, I'm sure . In the Theory of Operation for Defender . 7p is a 74ls04. Of course I have found typos within this guide. But this chip is labeled 5 times in the diagram - all showing a 74ls04
 
For posterity, I had this exact same issue. Unfortunately none of the methods described above seemed to work for me. I remembered a crystal oscillator circuit I used once that was very similar to the one in Defender, but it used a 74HCU04 as instead of 74LS04. 74HCU04 is unbuffered, and since the circuit is using several stages of the inverter, I thought it might have some effect on the timing. Sure enough, it got rid of the flashing vertical lines.

Another approach might be to use a 12Mhz TTL oscillator chip (like ECS-2100AX-120) and feed its output to the rest of the circuit, ridding oneself of this slightly flaky circuit.
 
For posterity, I had this exact same issue. Unfortunately none of the methods described above seemed to work for me. I remembered a crystal oscillator circuit I used once that was very similar to the one in Defender, but it used a 74HCU04 as instead of 74LS04. 74HCU04 is unbuffered, and since the circuit is using several stages of the inverter, I thought it might have some effect on the timing. Sure enough, it got rid of the flashing vertical lines.

Another approach might be to use a 12Mhz TTL oscillator chip (like ECS-2100AX-120) and feed its output to the rest of the circuit, ridding oneself of this slightly flaky circuit.
I got 7404s from somewhere years ago. like non-LS. the flip flops in the row 7 circuit you can use LS or HCT 7474s, but not anywhere else I discovered. I bought 74HCT74s not knowing the difference way back when, they're suitable replacements. those chips take the most abuse, so it's fairly common to get black screen of death. or in some instances the game will still boot, but I think it's missing the frequency for the video output so it's just black.

pretty wild
 
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