CNC Circuit Board Repair and Eeprom Chips

[JonesPrecision]

Hello,

First post here. I hope I have to come to the right place. I've been playing with electronics all my life and am now finally reading more about them and learning the theory behind circuit design. A project has come up recently that I wanted to do a little research on before I start. I recently acquired a Hardinge CNC lathe and it is throwing an error. The error relates to the main control board and two eeprom modules that store the ladder diagrams for the machine. This machine was built in 1988.

I have some standard test equipment and will likely be purchasing a scope in the immediate future. I am able to test circuits for simple things but I have no idea about eeprom chips. The problem either points to 2 bad eeprom chips (which seems unlikely that they both went at the same time), a dead battery that saved the memory (hopefully) or part of the main control board being the problem. I don't have power to the machine quite yet but when I do I will start with the batteries and work up from there.

My two biggest questions are is there a way to test the chips without erasing whats on them and is there a way to see if the board is effectively communicating with the chips? A repair of this magnitude is going to cost be about $1500 and a board replacement is somewhere in the neighborhood of $5k so I would like to troubleshoot it myself initially.

The data that is stored on the chips is absolutely vital to the way machine runs. Losing that data means I need to pay to have it repaired or scrap the machine. I would like ot be able to back that data up in the future if feasible at some point so I can make copies but that would be after I get it working again.

Any help is appreciated.
 

[retrolefty]

The data that is stored on the chips is absolutely vital to the way machine runs. Losing that data means I need to pay to have it repaired or scrap the machine. I would like ot be able to back that data up in the future if feasible at some point so I can make copies but that would be after I get it working again

 The biggest problem is that maybe you have already lost critical data? That error could mean the EEPROM data may fail a checksum routine. If you don't have a way to validate the data presently in the chips then you are taking a risk spending too much time and money trying to repair it yourself. Check if the chips are receiving proper Vcc voltage(s)
as that could be fixable locally.

[jwm_]

First we need to know the chip part numbers to begin to answer the question. A picture of the chips on the board and what surrounds them couldn't hurt either.

eeprom chips are pretty robust and would strike me as an odd failure point, it is highly likely you will be able to read out the data if they are of any of the standard form factors.

[JonesPrecision]

The battery I was referring to in the first post was for the whole machine and if that goes dead you lose all parameters and have to reenter them. The machine battery doesn't seem dead but I know this error can be related to them going dead.

I know there is a chance that data is lost and in that case the machine will needed to be repaired regardless. There are people in the industry I might be able to reach out to that have the data stored on the chip and I'm assuming then I could just rewrite that on a new chip but I'm not there yet. Hoping it doesn't have to go that far.

Was just taking photos of them because they are stuffed way in the back corner of the machine and I couldn't read them without taking the board out. The chips are Toshiba TC57256AD-15. They are labelled E-1 and E-2 on the stickers.

[JonesPrecision]

Here is another photo for good measure but I'm not sure it shows anything more than the first. From researching this problem it seemed highly unlikely that both chips would go at the same time and the problem lay with the board.

My first order of business is getting power to the machine which will be hopefully sometime next week. When I do I will need to enter about 500 strings of paramaters because every time you hit this error you have to wipe the memory. Super fun! I will start with replacing the batteries first which you are supposed to do with the machine running so as not to lose the parameters but if I can't get past the error and have to redo it over and over again I might as well do that. Failing that I will check some voltages as I know failed power supplies are common and can throw out all kinds of errors. Planned on looking the board over very carefully in the next few days for any tell tale signs of blown components as well.

If none of that works then I guess I will be concentrating around the eeproms themselves and then off to repair when I can get the money but I'm hoping (fingers crossed) its something simple (like the batteries).

[jwm_]

Those look like standard eproms, not eeproms and you should be able to read them with any generic EPROM programmer or you can rig something up with a board like an arduino if you have one laying about. You need to supply them with 12v in a specific pattern to write to them, so you have pretty much nothing to worry about homebrewing something to read them at 5v if you don't want to accidentally write to them. Just treat them with the care you would other ICs.

It is unlikely they are the cause but I can understand wanting to back them up before poking around.

[JonesPrecision]

Haha like I said I don't know a lot about these chips. Maybe not even their name! The error I'm getting is a well documented issue and I only know what I've learned from threads relating to it...so far. Unfortunately they usually stop at "send it in for repair".

That doesn't sound too bad. I've seen eprom reader/writers for under $20. Is it safe to say I could use one of them to back it up? I've read about guys wanting to change the data and needing a special unit from the CNC control manufacturer but I have no reason to change anything. I just want to safely store the data and if needed restore it at a later time. Guess I need to do some more reading on these chips.

Thanks for everyone's help so far.

[JonesPrecision]

Found a datasheet:
http://www.datasheetlib.com/datasheet/733782/tc57256ad-15_toshiba-semiconductor.html

[EPTech]

Hi there,

I have got a minipro programmer that can read that EEPROM. It is an ebay cheapy that I acquired recently and so far I am very pleased with it. I think is is around $50.

[rf+tech]

JonesPrecision,

The single most important piece of information that will determine your course of action lies with the checksum, stored in each EPROM.

If any single EPROM throws a checksum error, that chip *must* be reprogrammed with a copy of the original data of the proper revision. This data may be obtained from another identically marked chip on a known working board.

EPROMs store data by virtue of an electrical charge injected into the floating gate of individual mos transistors. This charge does leak off slowly over decades, resulting in bits changing state. The term used to describe this failure mode is "bit rot" and is detected at boot-time when the newly calculated checksum fails to match the checksum stored within the chip itself. The manufacturers datasheets typically state a 10-year data retention specification. That most of these aging EPROMs still pass checksum at three times the 10-year spec is a testament to the cleanliness of the fabrication process. But electrons are still leaking from the floating gate and time is running out.

If the error does *not* indicate an EPROM checksum failure, the problem lies elsewhere and may very well be the machine parameters have been lost from battery-backed SRAM. Getting power to the machine and a fresh new battery should be completed before attempting to reload machine parameters. So in this regard, you are already on the correct path. Failure of single cells or entire rows within SRAM is another consideration, it is rare but definitely happens.

Others will offer their hobbyist-level suggestions for DIY. Naturally, I am a bit guarded about specifics as my income relies on years of electronics at the professional level in that industry and knowledge gained through years of component-level diagnostics/repair in the machine tool field.

RF+ Tech

[JonesPrecision]

RF+ Tech

Thank you for the very detailed answer. The error I'm getting is a 998 rom parity error and when on screen it points to both eproms.  From what the previous owner told me it was fine and then the error showed up and both were listed on the screen. I know its not very common that both are listed and I was thinking that something might be wrong with the board itself.

All of the fanuc manuals I have read say either the main board or the rom modules are to blame. I do remember someone online talking about chksums like you explained but I don't see it listed anywhere in the manual.

If I am able to fix it  then backing these up is still probably a good idea or even replacing them with new chips.  Considering the bit rot you explained it sounds like I would want to take care of that anyway.

[rf+tech]

JonesPrecision,

If the ROM board cannot be addressed/read from, then both ROMs would be implicated. The 5 Volt supply should be checked right at the main board and ideally at the ROMs themselves. I*R drops through the wiring harness are then taken into account. The TTL Vcc spec is 5.0 +/- 0.25 Volts (+/- 5%) at the chips.

Checksums would never be in the manuals, they change with each firmware revision and are stored in the ROMs themselves at the time they were first written. The boot-up self-test routine calculates a checksum on each ROM as a means of detecting corrupt code to guard against damage/unexpected behavior and save troubleshooting time. Nothing like spending hours looking for a hardware/electrical fault only to find out after a $5k board swap it was corrupt code in an EPROM. The checksum cuts to the chase very first thing and alerts us with the error code that it's borked.

Do report back when the machine has been wired in on-site.

RF+ Tech

[JonesPrecision]

I will, thanks again. On the plus side the lathe came with a bunch of additional parts from another Conquest 42 lathe but it was an OT-C machine. I do have an extra power supply that goes on the main board and the numbers match. At least I have a backup.

[Marc M.]

I've been a CNC tech for about 10 years now.  I've run into a parity alarm getting thrown once or twice during that time on Fanuc machines. It was never actually the ROM. Instead it was other causes which unfortunately, I don't recall what they were.  I'm thinking one had a problem on the CPU board (newer control, maybe a 31i ) and another was possibly something shorted somewhere on the machine causing a "black screen of death" and popping up with a parity error but I very well could be mistaken. Alarm messages are often misleading so you always have to take them with a grain of salt.

In any event, the ladder is written by the machine tool builder and not Fanuc. The ladder contains all the logic to interface your machines hardware with the Fanuc side.  Items such as automatic tool changers, pallet changers, safety interlocks, etc. are all controlled via the ladder so it will be very specific to what hardware options your machine has. In case you do have bad ROM(s), I would get in touch with Hardinge with your model and serial # and see if they can e-mail you a copy of the ladder for your machine. We've had mixed luck with manufacturers being able to provide data like ladders and parameters on machines that old and even one that was only a couple of years old.

If they are unable to provide it, I would ask over at Practical Machinst (www.practicalmachinist.com/) and CNC Zone (www.cnczone.com/) if anybody has the same machine that would be kind enough to send you a copy of their ladder. If there are differences in hardware between the machines you may still need a copy of fladder (big $$$ to purchase from Fanuc) to edit the ladder to make things work.  If the ladder you get has extra hardware it would be possible to change the ladder to get it to run on your machine. If on the other hand your machine has hardware that the ladder doesn't support, adding support for it is probably not feasible.  I would also suggest that you post your issue on both those sites also as there are many folks much more knowledgeable than myself with Fanuc control issues.

[EPTech]

Hi There,

I used to own an old Ikegai FT-20Z lathe with Fanuc 11T control. It had a PMC cassette that held the manufacturer specific data, like ladder, timer and relay parameters. Your board seems to have the PMC in the two eproms on board, right? Must be a more modern controller. One thing I know about PMC data is whenever it gets corrupt or erased, you need to either contact the machine manufacturer or find someone with exactly the same machine (possibly options and all) and kindly ask for a copy of the eprom data. Maybe if you explain your case, he or she will be keen to make eprom masters him or herself and give you the JEDEC file.

Good luck.

[JonesPrecision]

Machine is OT-B control. I have been in touch with a very forthcoming application engineer from Hardinge so it's possible he could help me out with the ladder if need be.

I'm doubtful its actually the eproms but you never know. I just want to be prepared if it is. I was thinking the other day about the PO told me and he said he was able to reset everything, input the 900s and regain partial control of the machine but when he powered down again they were gone. I completely forgot about that and now that leads me to believe the batteries need changed. Hoping its something that simple. Appreciate everyone's help.

I did reach out on PM and got very little feedback which surprised me although my initial search was filled with older threads relating to the issue and I was able to learn a little from them. I'm guessing since its an older control the majority of guys who use this stuff every day have upgraded controls.

We'll see what happens in the coming week. Either way I will probably go ahead and backup whatever data I can from the chips if I get it figured out. I'm assuming even thoguh I don't have the Fanuc software an eprom reader/writer will be up to the task and safeguard me from certain headaches in the future.

[jlmoon]

FWIW.... I would be looking for battery backed up non-volatile ram such as a Dallas DS-12XX series part or similar.  There could be a backup battery styled part that has lost it's ram data which likely is the configuration data / parameters for your particular machine.  If so, you're going to need the manufacturer to assist you on this one unless you have a series of data values to work with.  Those EProms look to clean, pretty and new to be bad and they don't fail very often. 

Best of luck, hope you find the source of the problem

JLMoon