Robotron Woes x 2

tb lilley

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I have a couple of Robotron boards, with a fault on each.

First up:

11510E27-A5FB-4CEF-8BE7-6F97A07A0F23-5514-000002FC57D20353.jpg


This is a known tested working monitor. Game plays fine, but colours all wrong. Cab wiring is fine as I don't get this problem with my other Robotron board. Have swapped in known working video decoder chips - no change. Both decoder sockets test good. The board passes all ROM and RAM tests. I'm all out of ideas ... any suggestions of where to go next with this?

Next up - on my second Robotron board I have a common enough fault: CMOS RAM problems. I've had niggles with CMOS RAM on this board ever since I've had it. It used to fairly regularly lose all settings - and this could happen after the game had booted fine with no errors. Walk away and come back 10minutes later and all values set to 7. All high scores read 777777. Number of lives per player? 7777 etc etc. I thought I'd solved this when I replaced the 5114 with an NVRAM kit, but the problem soon started happening again. Last night I replaced the NVRAM kit with vanilla new 5114. Same as before, game can play fine, but keeps losing settings. At this point I'm ruling out problems with the 5114 - so where else should I be looking? Right now I cant get the game to boot with anything other than 777777s everywhere, so whatever was flakey has finally gone kaput. If it makes a difference this is a Stargate board that I've converted to Robotron - bit even when it was used with Stargate I had the exact same set of problems.

Thanks.
 
First up: I'm all out of ideas ... any suggestions of where to go next with this?

Next up - so where else should I be looking?

1st board: What do you get in the color RAM test mode? The one that cycles thru 3 shades of red, 3 shades of green and 2 shared of blue (2 seconds per color). Also, what do you get in the solid red, solid green and solid blue test screens? Finally, what do you get on the "color bars" test screen?

2nd board: If the CMOS RAM is known-good, I'd perhaps be looking at things in the chip-select logic, such as the NOT gate in 5A (pins 1-2), the 7410 @ 6I and transistor Q13, or the decoder at 4G. Sounds like maybe the CMOS isn't being selected, and your reading junk on the data bus, or some other memory somewhere.
 
Thanks, I'm all packed up for the evening (11pm here) so ill check colours in RAM test tomorrow. I did cycle through earlier this evening. Red is barely visible on RAM test - it is there, but just very very dark. I think blue and green the same. On the RAM test screen that displays the different colour bars - yeah, bars display, but colours are dark. Pretty sure pink is missing - I'll have to report back tomorrow.

On board 2 - I've got a very limited amount of test equipment I.e a multi meter ..... So I'm going to struggle with most of that. Might be one I have to send out for repair. Whatever the problem was, it was intermittent but is now permanent. Thanks for the advice. Much appreciated.
 
Just finshed up a board that was doing the color thing. I rebuilt the entire video output, chips transistors. pulled all the resistors and check values. Turned out it was one of the 74166's. Aaaaarrrrggghhh!

On the second board, are you running it on a switcher?

ken
 
Board#1
Here is a post that can probably fix your color problem on board# 1 (also assuming that you checked your ribbon cable connection, etc...)

See post #13 of this thread:
http://forums.arcade-museum.com/showthread.php?t=252952&highlight=color+cocktail&page=2

I had a Stargate board that was doing exactally what your Robotron board is doing - this procedure fixed it.

If you have a logic probe, you should be able to pinpoint the bad ic almost immediately.

I immediately detected the failed ic on my board and replaced it - it was indeed a failed 74166 as YellowDog just stated in the previous post.

Follow the instructions in the other thread to boot up in cocktail mode to see if that temporarily fixes the color problem. Then you should be able to track down the failed ic.

Board#2
You said that this board is a Stargate board? Is it a "Rev -" board? Did you make the mods to the board so that it would be compatable with Robotron/Joust/Sinistar?
http://www.robotron-2084.co.uk/techwilliamscpubsbamod.html
Have you also done the lithium battery mod? If you're using the original Williams battery holder, even though it may look okay, you may have a broken end on it which will not give you the voltage to maintain the CMOS. You can check this with a multimeter.
 
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Interesting. The cocktail flip ("screen control" line) trick LyonsArcade described in that thread is clever. I hadn't noticed how it has some duplicate components for cocktail mode. Nice troubleshooting trick to narrow down the issue.
 
Interesting. The cocktail flip ("screen control" line) trick LyonsArcade described in that thread is clever. I hadn't noticed how it has some duplicate components for cocktail mode. Nice troubleshooting trick to narrow down the issue.

As long as the other set of 74166s are good. In the case of the board that was driving me crazy, the matching 74166 failed in exactly the same way. So flipping looked the same. Which is why I was convinced that it was in the video output circuit.

Regardign the CMOS, it sounds like it is getting voltage. Otherwise you would be getting the three reset messages everytime you powered the game up.


ken
 
If you have been fiddling with it, installing the monitor connector off by 1 pin will cause similar issues. Check that your monitor signal plug is centered and that all pins are good before you go testing chips.

Lose a connection, and things can get colorful, in the wrong way.
 
Board#1
Here is a post that can probably fix your color problem on board# 1 (also assuming that you checked your ribbon cable connection, etc...)

See post #13 of this thread:
http://forums.arcade-museum.com/showthread.php?t=252952&highlight=color+cocktail&page=2

I had a Stargate board that was doing exactally what your Robotron board is doing - this procedure fixed it.

If you have a logic probe, you should be able to pinpoint the bad ic almost immediately.

I immediately detected the failed ic on my board and replaced it - it was indeed a failed 74166 as YellowDog just stated in the previous post.

Follow the instructions in the other thread to boot up in cocktail mode to see if that temporarily fixes the color problem. Then you should be able to track down the failed ic.

Board#2
You said that this board is a Stargate board? Is it a "Rev -" board? Did you make the mods to the board so that it would be compatable with Robotron/Joust/Sinistar?
http://www.robotron-2084.co.uk/techwilliamscpubsbamod.html
Have you also done the lithium battery mod? If you're using the original Williams battery holder, even though it may look okay, you may have a broken end on it which will not give you the voltage to maintain the CMOS. You can check this with a multimeter.

Interesting stuff. I would put it into Cocktail mode, but it already is - sheer laziness on my part. The board came out of a cocktail and I haven't changed it for upright. Yet. Still got to be worth trying replacing 74166.

On board 2 - yes, is a Rev - board, and yes, I've done the mod. I haven't fitted a lithium battery - but the NVRAM kit has a battery built in, so doubt it's a CMOS voltage problem.

The cab is running the original power supply. All voltages test great. Board 1 is running original 4116 and never misses a beat (apart from the color issue that's now developed). Board 2 is running 4164.
 
Well, if it is in Cocktail mode, flip it and see if it solves the problem. Either change works, from what was written.
 
Yes, definitely take board #1 out of cocktail mode...

It will be using a whole different set of chips (1i, 2i, 3i, and 4i) in standup mode and the color problem *should* go away providing that those chips are operating okay.
 
From the look of things, it is player one that is the issue. That is the I row of 74166's. If he tries player two, the screen should flip and hopefully clear up.

ken
 
I thought that when you are in Cocktail mode that you are actually using row "J". ??

I was having color issues on my Stargate with both P1 & P2. I did the +5v to pin 23 on Decoder 4, put it into cocktail mode using row J and the problem went away telling me that the issue is in row I. It didn't matter if I was P1 or P2, no color issues when I was in cocktail mode. When I was in standup mode, I was getting a red background on P1 & P2.

I pulled the +5v jumper and went back to regular mode and used a Logic probe on row I and found the IC that wasn't pulsing, replaced it, and all was well.

If he's already in cocktail mode, wouldn't he want to get out of it to be using row I??
 
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Cocktail mode uses row I (the normal upright row) and when it flips to player 2 it pulls the screen mode line high, which then uses row J (upside down mode). The Joust cocktail doesn't have the jumper on the I/O board so it always uses row I for both players (the same as the upright game).

So if he forces cocktail mode either by putting the jumper on the IO card and playing player 2 or manually running +5V to the screen mode line, it will switch to the J row of 74166's. Assuming that they are not messed up too, the screen should clear, but be upside down.

ken
 
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