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Repairing a Missile command cocktail arcade

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Hi,

 

I got my hands on a cocktail table with Missile Command few months ago. The previous owner said the game used to work but unfortunately the game doesn't seem to work for me.

This is the first time I will repair an arcade so I come here maybe to get some tips and wisdom :)

 

My overall goal for the repair is not really the look of the arcade (the leg would need a refreshment for example, and there is scratches here and there)., but more the game itself. So the board should run and I want the control to feel good (so some work on the bearing, maybe polishing the trackball).

 

After running the test mode it seems that I have a problem with the RAM. I have 8 high pitch beeps so it would mean that all the 8 RAM chip are dead.

So the next step for me would be to buy replacement chips. So I'm looking for the chip reference TMS4116-20NL. There is some sellers on internet but the minimum orders are often too high, made for professionals.

I also found this page http://4sale.sbszoo.com/but it seems it's used chip only. I don't really mind the 20$ minimum order if I can get my hands on this RAM chips.

Is anybody have experience buying such chip? Do you have any advice or good addresses?

 

Do you also know any reason why all the RAM chip would die? I plan to check the voltage, but maybe there is an other problem somewhere?

 

Anyway, thank you in advance for any help you could provide. :thumbsup:

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What type of RAM chips does it take... chances are better than even that you can source them from an old computer or graphics card.

Seeing that Missile Command is a fairly early game, chances are it uses quite low capacity RAMs, like 2K x 1, 4K x 1 or 8L x 1 bit.

 

In all possibility it's not the RAM that's entirely bad, it could quite easily just be a dud IC involved in the support logic. Luckily, many of those are just off-the-shelf 74LS* type ICs that are still available as new.

 

Additionally, if the RAM chips you happen to need are rare, there are alternatives like building a daughterboard and using more modern alternatives.

 

Of course, the "bad news" is that you'll have a bunch of diagnostic stuff to go through - if you could get your hands on troubleshooting info it'd make it somewhat easier. I'm sure I've seen sites that have such manuals online but don't have any links.

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Thanks for your quick reply Rybags.

 

The TMS4116-20NL chip is a 16K RAM chip.

I don't think it's especially rare. It's probably easier to find them than using a daughter board.

 

I've downloaded already the manual of Missile Command: www.mamext.net/manuali/missile.pdf

But I don't recall any indication on how to manually test ICs.

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16K RAM modules for the 800 computer use that type of RAM chip.

 

Probably likewise the 16K board that most 400s shipped with.

 

But, like I said - failed RAM test might mean a bad chip or two, or faulty external logic. Common test for bad RAM chips is to let the machine sit then finger-test the top of each chip and see if any are warmer than the rest.

Edited by Rybags

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When I first got my MC cabinet, the PCB had one bad RAM chip. I tried to replace it myself, but ended up making the situation worse, and had to send the board out for repair (which thankfully was done quickly and reasonably.)

 

In short, be careful with soldering and desoldering those RAM chips! If you're not confident in your soldering skills, you might want to practice on something nearly worthless (like a 2600 Pac-Man cart.) Or simply send the board away for repairs (this is the guy I used - Arcade Solutions web site )

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And where did you get your replacement RAM sdamon?

I'm fine to use other RAM chip (I'm sure the board have some tolerance) if it's working but I doubt I can just take any 16K RAM.

 

yeah the soldering can be challenging. I'm not an expert (far from it) but I already done some really precise soldering on modern consoles (no, not modchip). But my goal is really to repair it myself.

 

Oh and I live in Germany and I don't know any repair shop here.

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And where did you get your replacement RAM sdamon?

I'm fine to use other RAM chip (I'm sure the board have some tolerance) if it's working but I doubt I can just take any 16K RAM.

 

yeah the soldering can be challenging. I'm not an expert (far from it) but I already done some really precise soldering on modern consoles (no, not modchip). But my goal is really to repair it myself.

 

Oh and I live in Germany and I don't know any repair shop here.

 

It's been 6 years since I had that RAM problem, so unfortunately I don't recall where I got the RAM. Some Google searches for "4116 RAM" came up with the following... Arcade Chips site I'm not specifically recommending them, but the price sure seems right.

 

Before ordering the RAM, you may want to ask for advice on rec.games.video.arcade and rec.games.video.arcade.collecting (which you can access through Google Groups.) There's some very knowledgeable folks on there who may be able to help point you in the right direction - perhaps something else is wrong causing all the RAM to show as failed.

 

If you do turn out to need to replace the RAM, you may want to clip off all the legs of the malfunctioning chips, then remove the the legs from the board one by one. Wish someone had suggested that to me before I attempted the RAM replacement... it might have gone better. Also be sure to add sockets to the board instead of soldering the new RAM on directly.

 

If all else fails, you can send the PCB to a repair shop in the US. You'll probably pay more in shipping than you will for the repair, but if it comes to the point that you've tried and failed to fix it yourself, it may be worth it at that point. Here's hoping you can get it fixed yourself - MC is a GREAT game to own once it's working right!

Edited by sdamon

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Hi,

 

I got my hands on a cocktail table with Missile Command few months ago. The previous owner said the game used to work but unfortunately the game doesn't seem to work for me.

This is the first time I will repair an arcade so I come here maybe to get some tips and wisdom :)

 

My overall goal for the repair is not really the look of the arcade (the leg would need a refreshment for example, and there is scratches here and there)., but more the game itself. So the board should run and I want the control to feel good (so some work on the bearing, maybe polishing the trackball).

 

After running the test mode it seems that I have a problem with the RAM. I have 8 high pitch beeps so it would mean that all the 8 RAM chip are dead.

So the next step for me would be to buy replacement chips. So I'm looking for the chip reference TMS4116-20NL. There is some sellers on internet but the minimum orders are often too high, made for professionals.

I also found this page http://4sale.sbszoo.com/but it seems it's used chip only. I don't really mind the 20$ minimum order if I can get my hands on this RAM chips.

Is anybody have experience buying such chip? Do you have any advice or good addresses?

 

Do you also know any reason why all the RAM chip would die? I plan to check the voltage, but maybe there is an other problem somewhere?

 

Anyway, thank you in advance for any help you could provide. :thumbsup:

 

 

before you start removing chips, if you have a schematic, including powersupply, start by checking ALL voltages, also check your DC lines for AC Ripple

 

look for bad capacitors in the power supply and on the circuit board. bulging electolytic capacitors, or ones that have obviously leaked something. a MC game is probably about 25-30 yrs old or so.

 

voltages should (in my opinion) be within plus or minus .5 volts of their rating. a lot of supplies are rated +- 1v but I'm picky :)

 

when checking voltages, do it carefully and with a load on the powersupply (even better if there are test points on the PCB for voltages)

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TMS4116 are MOS, TTL compatible DRAM chips. 16384 x 1, and were available in 150, 200 and 250 ns version. you can go faster but generally not slower.

 

they are 3 voltage chips. Pin 1 is -5V, pin 8 is +12V, Pin 9 is +5V and Pin16 is ground.

 

datasheet is available at: TMS4416 datasheet

 

I'm about 90% certain that the chips in the 400/800 16K ram module are compatible.

 

if your RAM chips are socketed, remove them one at a time and re-insert them, corrosion may have caused high resistances and made them seem to fail.

 

the TMS 4116 crosses to NTE2117 if you have NTE parts available.

 

here in the US, Unicorn Electronics sells the chip fairly inexpensively. I think they have a $25 min order though.

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ok, so I finally got some RAM chips ans sockets to be able to replace them later on if necessary.

 

I also measured somes voltages:

- The voltage of the board is ok since I measured exactly +5.0V

- For the RAM chips it's different. The +5V and +12V varies but usually stay in the tolerated range (+-10%), however the -5V are often around -5.7V, -5.8V.

I will change the chips anyway since the test mode tells me they are bad but should I worry that this bad voltage could be caused by something else on the board? If yes, how do I track that?

 

Thanks for your help!

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