Star Trek SOS repair - not my idea of a good time

gamefixer

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Even though I've been in the Coin-Op business for going on over 30 years I've spent very little time actually working on G08's. I've fixed maybe less than 10 in that time frame. BITD when we had a game with a G08 that took a dump I ripped the G08 out and dropped a K6400 in its place.

In hindsight that doesnt help me much now since that supply of k6400's is long gone. Probably should have spent the time on the G08's. :(

Well, this Star Trek came to my shop about two months ago and I knew I was going to be in for a ride. Its in a Sega Convert-a-cab with the usual beat to smithereens bottom, so build a new bottom.

Unknown condition G80 board set (first one I've ever had to trouble shoot).

Unknown condition G08 (aka it doesnt work).

So I move onto the easy part, the base of the cab. :)
 

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more pics of the base.
 

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The onto the board set. I bought one of those Vector Labs G80-->ATX adapters since I knew that the factory power supply was a piece of crap even when it was new. I installed the ATX supply, rebuilt the DC harness on both sides with trifurcon(sp?) pins and new molex connectors, double checked my work, triple checked my work and then put it all in the game (with the monitor unplugged).

Upon first power up, the +12VDC fuse on the VL board blows. Ah hell.... Check my work again, everything is fine so I solder in an inline glass fuse holder and put a 2amp fuse in the holder. Power it up and no fuses blow but I'm not greeted with the opening music that the game usually does. Well poop, board set issue.

I pull the cards out along with the back plane and put the boards on my bench. Sure enough, of the 6 boards I can verify that three are bad. CPU, XY Timing and XY control. Yay me.

with some help from another KLOV member I get the CPU working! :)
 

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this is where the endless frustration sets in. I started with the XY control board. At first it would draw nothing on the screen and it would peg the XY outputs to 4VDC and -3VDC. I eventually got it to draw an image but after pulling and testing EVERY SINGLE IC ON THE BOARD it would still draw random vectors on the screen (or does it?? More on this later).

Even after testing all of the IC's I managed to find two with shorted to ground pins with my multi meter. So much for the logic tester doings its job.

The XY timing board was causing the CPU board's LED to come on shortly after reset and stay on. Probing the board with my scope I found a signal missing from the LS74 @ U43. Replaced it and the CPU was now working right.

At this time I was using a scope and an G05 as a monitor. Since there is no Z signal connected to the monitor or the scope they were both drawing randomness all over the screen. I think its time to plug the G08 in.

BTW, while probing the XY control board I found the color outputs to be REALLY high. As in 10VDC sometimes. I put a load on the outputs this morning and that came right down to where it should be. Makes sense given that the drives are biased by +12. Whatever.
 

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And now we come to the G08.

So far I've completely rebuilt the monitor and only powered it up with the yoke disconnected and no signal applied. It does generate HV but something I find odd is that both the X and Y yoke pins are sitting at -65VDC. I know the signal wont swing without an input but should they BOTH be -65VDC?

I will probably apply signal to the monitor here shortly. From there I hope to see those pins wafting about rather than being pegged to one side.

About the random vectors. I'm hoping that some of the mess I was seeing on my scope and the G05 were the result of this signal being applied to the incorrect display. I guess we will see.
 

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Well, the monitor works! But the random vectors I was seeing on the scope are in fact present on the G08. :(
 

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Well, the monitor works! But the random vectors I was seeing on the scope are in fact present on the G08. :(

Well that's a start. The G08 looks good. Have you tried the working board set to see if they are still actually working? If I have too I'll dig out my dedicated game and see if those boards are still working and send the XY pair if nothing else.
 
Well, the monitor works! But the random vectors I was seeing on the scope are in fact present on the G08. :(

CONGRATULATIONS. You found your balls. LOL :)
(firing up a vector monitor for the first time after reconditioning it is pretty scary; now to fix the XY logic boards ...)
 
Well that's a start. The G08 looks good. Have you tried the working board set to see if they are still actually working? If I have too I'll dig out my dedicated game and see if those boards are still working and send the XY pair if nothing else.

Found out when I went back to the stack to work on them the boards that were in it are the "working" boards. So, they work but draw random vectors.

At this point I have no combination of boards that draws a correct screen and I have 3 of each XY board on hand right now.

My XY Timing board no longer locks the CPU up but does not draw a picture at all. X/Y outputs are both pegged.
 
CONGRATULATIONS. You found your balls. LOL :)
(firing up a vector monitor for the first time after reconditioning it is pretty scary; now to fix the XY logic boards ...)

Especially not knowing about the previous work thats been done to this monitor. I did go over it several times and made sure that nothing looked out of place though.

I'm just glad it worked.

These XY boards... thats a whole different problem.
 
And for the sake of doing it.

When I get this thing working correctly I'm going to take some heat measurements on the output heat sink configured as such.

1. Factory transistor position and factory fan power.
2. Factory transistor position with fan wired to 120VAC
3. Transistors moved inside with factory fan power
4. Transistors moved inside with fan wired to 120VAC

Just curious to see if one way is cooler than the others. My guess is that 2 and 4 will be almost identical.
 
And for the sake of doing it.

When I get this thing working correctly I'm going to take some heat measurements on the output heat sink configured as such.

1. Factory transistor position and factory fan power.
2. Factory transistor position with fan wired to 120VAC
3. Transistors moved inside with factory fan power
4. Transistors moved inside with fan wired to 120VAC

Just curious to see if one way is cooler than the others. My guess is that 2 and 4 will be almost identical.

That should be interesting. All of the conventional wisdom says to move them inside for better cooling but I've had several very knowledgeable folks tell me to just leave them alone.
 
I always questioned that idea... The point of the heatsink is that the heat "sinks" to the aluminum heatsink from the transistor via the thermal grease, and the heatsink itself provides the surface area to dissipate that heat into the air flowing from the fan... The bottlecap itself provides very little surface area so i can't imagine the air flow on it itself would make a significant difference

If anything a bigger/better heatsink (more surface area) would be the way to improve

Anyway some emperical results would be interesting, and good luck with your repair!
 
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I had done a rebuild on a G08 recently, among some other work. I followed the excellent guide here:

http://www.biltronix.com/Star_Trek_08.html

Seeing as you're much more skillful than me at repairs, I suspect you shouldn't have any issues if you go the full rebuild route. So great when you turn it on and it works, keeps working and doesn't catch fire! I did flip the bottle caps, too. :)

I've got a spare cage and complete boardset as well - it's got the ROMs for TAC/SCAN on it and it's working with the following issues <IIRC - been months since I touched it; my work schedule changed and I've not had time for any projects at all this year :( >

Rundown:
Main/ROM board is okay and working
One of the XY boards creates some random vectors but does render the picture correctly
There's some buzz on the sound PCB or something like that

I *think* that was all the issues.

LMK if interested in the set.
 
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I had done a rebuild on a G08 recently, among some other work. I followed the excellent guide here:

http://www.biltronix.com/Star_Trek_08.html

Seeing as you're much more skillful than me at repairs, I suspect you shouldn't have any issues if you go the full rebuild route. So great when you turn it on and it works, keeps working and doesn't catch fire! I did flip the bottle caps, too. :)

I've got a spare cage and complete boardset as well - it's got the ROMs for TAC/SCAN on it and it's working with the following issues <IIRC - been months since I touched it; my work schedule changed and I've not had time for any projects at all this year :( >

Rundown:
Main/ROM board is okay and working
One of the XY boards creates some random vectors but does render the picture correctly
There's some buzz on the sound PCB or something like that

I *think* that was all the issues.

LMK if interested in the set.

That Biltronix site, thats a good read.

I had already ordered and installed new square male pin headers everywhere with the exception of the fan and degausing coil connections, replaced all female connectors (the two on the paddle boards), replaced all of the potentially high current and important single wipe pins in the female molex's with trifurcons(sp?) and also repalced the single wipe pins in the video harness as well. At this point I'm fairly comfortable with the monitor working as it should.

I just have to get at least ONE combination of XY boards to produce a glitch free picture. There is one set that does it less than the other two but thats not really helping me.

I suspect that all of the XY timing boards are to blame here. I've gone over my XY control board multiple times and can find nothing wrong with it. My XY timing board is brain dead at the moment and the other two I currently have on loan inject random vectors.

I think I'm good on boards right now (as in I dont need anymore) but thanks for the offer. I'm sure there are lots of reasons that an XY timing board would crate random vectors and when I figure out the one I have I will be sure to post that info here and in the G80 repair thread (I figure it would be good to have there in case it gets stickied.)

Buzz on that sound board is probably bad caps.
 
send the XY pair if nothing else.


I hate to ask you to do it but that would help me a lot right now. At the very least I can narrow down "where" the random vectors are coming from and then get it fixed. I suspect its the XY Timing boards that are doing it though.

I've not ruled out the back plane either although it looks good. If you have another one of those I'd like to use it as well.
 
I always questioned that idea... The point of the heatsink is that the heat "sinks" to the aluminum heatsink from the transistor via the thermal grease, and the heatsink itself provides the surface area to dissipate that heat into the air flowing from the fan... The bottlecap itself provides very little surface area so i can't imagine the air flow on it itself would make a significant difference

If anything a bigger/better heatsink (more surface area) would be the way to improve

Anyway some emperical results would be interesting, and good luck with your repair!

Yeah, like I mentioned I think that scenario 2 and 4 will be the coolest but will be about the same.

The first time I saw a k6400 I was very impressed with how cool it ran. Wells did a great job of adding more "sink" to that monitor and man did those things run great. It would be nice to add more meat to the G08's heatsink but I dont think that over heating is what causes them to blow up. Its that shitty factory supply and the ground potential that can swing all over the place.

The guy I worked for had about 50 of them but they slowly started to disappear, I think he thought I was coming back to the shop in the middle of the night and selling them... We got them from Exidy when they scrapped a bunch of Top Gunners and Vertigo's.
 
That should be interesting. All of the conventional wisdom says to move them inside for better cooling but I've had several very knowledgeable folks tell me to just leave them alone.

I'm pretty sure that moving them will have little to no effect on the temps.
 
Here's hoping you can answer a couple of questions for me that might also prove useful to others in the future.

I'm trying to use a logic probe on the cpu board. Where would I be able to clip the red and black leads on the cpu board to power the thing? The test points for +5?

I'm trying to probe the "coin drop" signal; if I ignored the logic probe and tried to use my DMM, would that likely pick up the coin drop pulse or would it probably be too fast for the DMM to register?

At the moment I'm trying to probe pin 9 of the 74LS00 in U6 but I'd want to hit pin 10 as well for the switch NO line and pins 12 and 13 for the NC line.

Edit: I found some +5 and ground connections on the Z80 but I can't possibly clip the alligator clips on the logic probe to chip legs, they're way too big. What to do?
 
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I hate to ask you to do it but that would help me a lot right now. At the very least I can narrow down "where" the random vectors are coming from and then get it fixed. I suspect its the XY Timing boards that are doing it though.

I've not ruled out the back plane either although it looks good. If you have another one of those I'd like to use it as well.

I was out in the garage tonight looking for my stash of G80 parts. I thought I had another set of boards somewhere but I could not find them so maybe not. I did find enough G08 parts to put 2 monitors together but I only have one frame,tube and yoke. I do have 2 back planes, one without the cage and one in the cage. I'll test my dedicated Star Trek tomorrow and if it's working I'll pull the XY boards and send with the back plane.
 
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