Problem Robotron RAM error 31, 131 error but power supply seems OK

[Robotgreg]

So I've got a problem with my Robotron which comes up with a RAM error on the initial boot up screen and then you can see the 131 error on the display on the PCB. It then tends to reboot.

I've tested the power supply and the voltages coming in to the CPU on the connector. and they all seem to be correct.ie 11.9 -, 4.9, 5.2.

I've also put some switch cleaner on this connector and have also reseated the ribbon cable between CPU and ROM board.

Assuming this problem is due to a power supply rather than the RAM which I'm led to believe is almost always the case with this type of error, what else should I be looking at?

This is about the limit of my technical ability.

Appreciate any help and guidance.

Cheers
Greg

 

[pooman2084]

I’ve had the odd RAM chip go Greg. The number displayed relates to the row and column of the chip on the board. I can’t remember from memory which way it goes but it should be obvious when looking at it.

Try carefully swapping the RAM chip with another if you don’t have spare and see if it moves the error.

You can get strange errors and resets if the ribbon cable isn’t seated properly or it just needs a wiggle and a push like on pinball boards.

Worth trying these first before working on your PSU which seems to read ok.

 

[Robotgreg]

Many thanks, Lloyd.

It could possibly be a RAM chip, but reading online, it seems that 99% of the time, that this specific RAM error, especially the 131, is symptomatic of a power supply issue so it would be a bit of a coincidence if it is this specific RAM chip.

Totally agree, power supply does seem OK unless I'm missing something.

I'll try again with the ribbon cables but did think that I had reseated them properly.

Thanks for your suggestions,
Greg.

 

[DanP]

I found a lot of issues like this can be fixed by making sure the connectors and connector pins are in good shape and making a good consistent connection. I fixed a Stargate with similar issues by reflowing all the connector header pins. Weird I know!

 

[Robotgreg]

Thanks, yeah did see that could be one cause. Sadly beyond my skills but will see if can get someone to do for me. I have tried switch cleaner with no joy.

 

[Lastspaceship]

Had bad ram on mine for what it's worth too. found this guide useful if you haven't seen it, appreciate some of the fixes get a bit deep: https://www.mikesarcade.com/cgi-bin/spies.cgi?action=url&type=info&page=Williams-hardware.txt

 

[chadsarcade]

Hi Greg,

As the others have said - clean and re-seat connectors etc. Your PSU sounds like it's OK - is it the original linear PSU? Is it using 4116 RAM or have you fitted 4164s?

RAM is tested in the order Bank 3, then Bank 1, then Bank 2. Usually if a single RAM has failed it will display the number for that RAM, but I've seen it before when it displays the first RAM tested when another has failed (hence 131)
If you don't have a RAM tester and have time on your hands:
Remove all RAM
Power up the board - you'll get a 131 error
power off, install RAM 131 (ie the RAM of the error code), power up. You should get a 132 error.
Rinse and repeat, the error should always be the next empty socket in the order the RAM is tested. After 138 it should jump to 111 through to 118, then to 121 through to 128
If the error doesn't move in this predictable pattern, the last RAM you put in could be suspect.

Of course, it might not be RAM, TTL in the RAM addressing circuit or elsewhere may also cause similar fault codes

Good luck!

Chad

 

[Robotgreg]

Hi Chad

Good to hear from you buddy and many thanks for all the information.

Unfortunately I've not been able to make much progress and have in some ways taken steps backwards rather than forwards.

I also have a Joust (my first ever machine from 92), so I thought the easiest thing to do would be to swap the RAM board from that machine with Robotron and see if the fault still exists, which I suspect it would do.

So I switched on Joust but unfortunately it came up with rubbish on the rug screen and then kept rebooting. Pretty much like Robotron and reporting a similar but slightly different error on the screen of RAM error 32 although the same 1:31 error on the display on the ROM board.

I cleaned.all the connectors with switch cleaner, initially the RAM boards and then the ROM board and it then booted up and I was able to start again game.But then the controls stopped working. So I then cleaned the contacts on the interface board and sadly, the game then reverted to the same rug pattern and 131 error and I can't get it to come boot up again properly.

Since it is reporting the same 131 error which I was able to.Solve, albeit not.Properly with cleaning the contacts. I do suspect it is to do with that, but.It's now got to the extent of my ability as I'm not able to reflow header pins etc.

However, I did think I could still swap the RAM board over and see what happened. However, the RAM board has been previously repaired and now has a couple of wires directly soldered onto the back which I'm reluctant to remove so I'm now pretty much stuck..

I've tried removing RAM chips in the past but tend to end up bending their legs because they always seem to be splayed out when I'm trying to refit them And given the the test on Joust seems to suggest that it's not actually the RAM chips, I’m not sure, I want to risk breaking any chips when it's unlikely to be the problem.

To answer your original questions, it is the original power supply.and the chips are. 4116.

I think I'm just going to have to wait until I can get some to have a look at it.

Thanks again
Greg

 

[chadsarcade]

Hi Greg,

Likewise - nice to see some of the old guard from the last millennium are still about

Your plan was sound - Joust and Robotron CPU boards are interchangeable and that should have worked. I'd suspect it's likely the interconnects and molex connectors which thwarted your plan. It can sometimes help to push the ribbon connectors home, then back them off by a mm or so. Note that the game will boot with just the ROM board and CPU boards connected which can be useful to take the other boards out of the equation.

The wires on the CPU board might be a factory mod, unless they are obvious track repairs. Some Stargate CPU boards were modded at factory with the "BS.BA inversion" mod to make them run Robotron/Joust which involved a couple of track cuts and wires. Stargate boards usually have a small upside-down PCB in one of the chip sockets so you may be able to ID it from that (or the part number if you look it up)

I'm with you on removing/replacing RAMs, lost count of the number of times I've bent a leg out and probably ruined what was a good chip.

I too have Joust and Robotron cabs (also Defender, Sinistar and Stargate) and have kept them on the original PSUs, but I have converted some of the CPU boards to use 4164 RAM - it's easier to find and runs cooler... but is non-original.

Good luck with it, I'd b surprised if you have done any further damage, it's likely just those connectors. I know you said you have cleaned them but if they look tarnished at all, you can rub them down with some fine sandpaper. Depending on the molex connector types, you may be able to carefully release the locking tab on each metal insert and gently pull them free of the plastic housing for a clean too.

All the best,

Chad