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Fanuc 18MC 916 DRAM Parity Error Recovery Help


Jun 30, 2015
Saint Paul, MN
As the title says, my mid/late 90's Mori Seiki SV50 just dropped a 916 bomb on me. I have Parameter backups but have never inserted a card into the slot to back up whatever is available there. LED's on Main Control say RAM Parity error on Main CPU.

I read to Restart with RESET and DELETE held in and start reloading Parameters, but is there anything else a guy should check first? Like Hardware issues for example? Fried boards etc.?

Are these errors ever cleared by simply restarting?

Oddly enough only 2 days ago I just wired in a new to me SH-50 Mori of the same vintage. Completely different 200 amp circuit, but maybe the SV noticed and is having a fit about it. :-)

Here's part of the build sheet. Anything here DRAM?
I notice these part numbers don't exactly line up with wha I see in the Maintenance Manual.


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The DRAM is used by the system firmware after booting the control. For a parity error in DRAM, initializing the SRAM is likely to do no good.

The way the 16/18 controls work is that the system software and PMC are stored in FROM. On booting the those files are loaded to DRAM for operation. Part programs and parameters are stored in SRAM.

The DRAM module is in the upper left corner of the CPU card. I suspect yours will be a A20B–2902–0461.

Have you tried cycling the power to see if a reboot clears the alarm? It may. If not, then replacing the DRAM module is needed. Pulling the CPU card from the rack will cause it to lose the backup battery connection and may result in loss of SRAM memory. There is a capacitor that is supposed to retain the power, but I have found that as these controls age the capacitor loses much of its ability to hold the SRAM. In other words, don't be surprised if on startup after messing with the CPU card, you get an SRAM parity alarm. Initializing the control is the recovery for that.

Back up your SRAM to an SRAM type PCMCIA card using the Boot Load procedure in the maintenance manual. Having that makes SRAM recovery after initialization easy.
Thanks tons Vancbiker. I'll try a restart first. If that fails I'll try the card. Is the one in the pic proper for this? I used this on my 18i lathe were the slot is next to the screen. Saved out from the lathe what it would accept. The lathe files are still on there which I can recapture later when this is fixed.

Think I should Format the Card first or maybe good to go after being on the lathe?

I've always wanted to plug a card into the Mori 18 slot, but figured that nearly 30 years of fan sucked dirty shop air passing thru the slot, would make it very hit and miss if the pins would even all connect in the first place. Guess I'll find out now. Always wanted to spray some of that super clean alcohol thru it. (Can't recall what it's called)

My card..
SV50 card.jpg
You can plug it in "hot" on the 18i.
No experience with this on the 18.


Think Snow Eh!
That looks like a CF card in a PCMCIA adapter. It may work. Some versions of 16/18 did not like CF but work great with SRAM based cards. No harm will come from trying it unless your card slot is as grimy as you imply. Never cleaned one, but using straight isopropanol(no water %) is OK by Fanuc on their boards so probably fine for the card reader too. You may need to delete the lathe files before backing up the mill files. Formatting should not be required.

It's always safest to install/remove cards with power off though most folks I've seen do it hot.
Now be sure to make backups of all files - system files, PMC - everything that can be written to the memory card. In the event of a serious board failure, DRAM can be bought for not very much money, and the files cost a diamond.
Think I'll get some of that alcohol and the proper card. Used to always keep the alcohol on hand but it disappeared during Covid.
Is this screen suggesting how big of a card I should get? I've heard a little about less is best on these old cards and Fanucs.

EDIT IN: What's this about a battery in these cards? I see on ebay they all say no battery, CNC Specialty doesn't talk of one other then it needs charging. How are these charged? Thanks for any help.

SV50 Memory Config.jpg
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Won't hurt to try your CF card. SRAM cards are hard to find and crazy money nowadays. Older ones used a button battery to retain the memory. Newer ones use a super cap that gets charged when inserted into reader. If left in a desk drawer for several months, it’ll be dead and contents lost. Of course the battery type lose contents too when the battery dies or is changed.
If you can find an 8meg that will cover any 16/18 Fanuc that I have ever seen that needs an SRAM card.

Since yours is a 18C, I suspect it will be happy with a CF card so no need to hunt down or deal with SRAM.
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All good news. Thanks tons!! Alcohol will be here Wednesday. A few squirts. A few blows, then have at it with more backup.
How did you know my card was siting in a drawer for months! :-)
A good bit off subject, but I know some folks in this thread can appreciate such things. My new SH-50 Cabinet. Machine looks a little or a lot rough depending on where you look, but inside the Magnetics cab it looks like the day it was born. Unbelievable really. No covers missing or wires hanging either. Purdy as they come...

SH-50 Magnetics.jpg
Well I did the alcohol squirt and air blow twice to clean off the pins inside the 18M control card slot, inserted my card into the control, turned the power on to the machine, then held in the two right most Soft Keys to start up the Boot Sequence. Nothing happened in the 20-30 seconds of holding in the Soft Keys, so I pressed the Power On button still holding the Soft Keys, heard a tiny click, and waited and still nothing. Went to look at the control and had 4 green LED's on top and the middle red LED on the bottom row. Books says "The System is stopped before the CPU is activated."

Shut down and tried a normal start, same LED's. Shut down and removed the card, machine came up normally.

According to the Maintenance Manual, anything after Version 5 of Boot Sequence 60M1 of the control, (mine is V12) the CF card should work. My CF card is installed in a PCMCIA adapter as pictured above, which was inserted with the centered guidance notched orientated at the top. Seemed to go in fine.

Not sure if I did something wrong or what. Almost seemed like the screen was not powering up during the Boot attempt. Regardless, the control obviously didn't like what was going on. At least nothing appears to have fried.
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Strange that a C model was not happy with the CF card. I've had enough issues with CF cards over the years it's why I quit effing with them and coughed up the money for an SRAM card.
SRAM help---

I'm running a Fanuc 16MB with a Powermate E handling the Carousel, and an 18MC on another machine.Do these machines run the 8k or 16k bus? And do I need Attribute Memory or not? I don't recall seeing this info in the books. Any idea what size a guy should get? Things seem to read like less is best.

In as such... Is anyone familiar with Vikant Corp. for SRAM Memory Cards? Their website is iffy and their Cart and Payment areas are unsecured according to Firefox. They seem to have what I need at about a 100 bucks less then CNC Specialty.

There's another place Amtron Technology Inc. that seems to have a few cards too. Anyone familiar?

Or in short... can anyone lead me to the best place to get an SRAM Card? Many thanks for any help.
The last one I got was from Memex but that was over 10 years ago. I don’t know about attribute or buss. Mine is 4 meg. An 8 meg will handle any of those controls. With a 4 meg, you might have to backup then drop some files to a Laptop to free up space to backup all of the control files.
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Can't help specifically with your question, but the 2mb SRAM card i have here at my desk, that we got from cnc specialty store, says "made in usa", so i suppose there's extra premium for american made?

Do you have the means to read an sram card on your computer? We have an old ibm thinkpad with xp on it, as well as the omnidrive pro usb reader from cnc specialty store.

Many pcmcia usb adapters won't read your sram card.

Yes, even READING THE FILES from an SRAM card is expensive.
"Do these machines run the 8k or 16k bus?" I have no idea what you are referring to.
Afik, you need attribute memory: all my cards have it, but I never tried without. Minimum size is 512k, but I prefer 4 Mbytes, which has always been sufficient..
True SRAM & FROM cards can be read from a pre-pentium laptop with DOS ver 6 and the PCMCIA extensions. Msflash.sys is a required driver for that to read the old cards from the powermate.


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Thanks all for the replies. I see it refers to 8 bit or 16 bit memory type. The one website says they no longer have the auto switching so "pick one." Which one???

My main shop host and programming computer is a Pentium 4 XP. I may be halfway home already as far as reading the SRAM cards. I do have a legacy ScanDisk CF reader off ebay that I was hoping would work. At least the PCMCIA fits.

Looks like I'll have to take my chances with the two companies I mentioned. They're both about a good bit cheaper the CNC Specialty.