Fanuc and Rats -The Saga

Well, we have this moderately aged Fanuc 3 axis router complete with a Fanuc 7M controller. This whole system runs punched paper tape.
Interestingly enough, this whole unit was given to us approximately 1 year ago complete with a tape punching computer and about 100 router bits!

Being more technologically advanced than our forbears, and the fact that the tape was a bit old and worn out, we decided that it needed upgrading to something a bit more reliable.
This decision resulted in the purchase in a BTR (Behind Tape Reader) unit which essentially plugs in where the tape reader was, and allows a PC to communicate directly to the 7M controller using DNC software.

This did not get rid of many problems, but rather generated a whole lot of new ones. We continuously come up with errors and rats get in the controller box and get fried. Just like send a file to the fanuc box, and an error pops up straight away.

We have pursued these errors, but with little reliable information, it is hard to pin down exactly what is causing them.
For instance, we get one that is the result of a parity check, meaning we have lost data somewhere. So we replace PC, replace cable, replace BTR, change settings, all to no avail. This only leaves the control box, full of memory chips and PCB's and other bits of retro circuitry.

This is becoming such a problem that I am nearly tearing my hair out trying to figure it all out. Personally I would love to biff the fanuc box out the window and put in plain and simple servo drivers. There is just too much junk in the fanuc box.

Q. What would you do?

Do the PCB's plug into a card rack? If so, then you need to totally clean the back plane, especially if it is of the wrapped wire type. The cards need to have their edge connectors cleaned with a pencil eraser. Pink Pearl is the best. Get some keyboard duster in a can to blow the back plane clear of dust and debris. If you have perfectly dry instrument air, no more than about 35 psi should be used. You can get a pressure reducer and a water trap to clean normal shop air, but be careful of moisture and oil in the air.

Then, I highly recommend you replace every electrolytic capacitor in the unit. I would imaging they are more than 5 years old and probably quite dried out. I have gotten more than one old machine to act close to normal with a cap-ectomy. You might scope the power supplies, you probably have either a +5V TTL or +12 cmos supply. Both of which do not like ANY ripple.

In so far as the rat problem, you are on your own.

just a quick $00.02

First thing to try with old controllers: Unseat the cards, take a rubber pencil eraser and rub the card edge connections. Then reseat the cards. I worked at a place that had a whole bunch of old Andrews EDM machines (this was in the '80's and they were old then), and that little trick solved a whole plethora of problems.

Second thing to do: Get a shop cat.

Alaric said:

Second thing to do: Get a shop cat.

Click to expand...

A pet boa or python works better.

I used to have a really big mean old tom cat. A couple of times a month he would come home with a snake. It would take him a couple of days, but he ate those snakes.

I'd look into possibly updating my resume and finding other work.

It used to be moths in the relays, now its rats in the PCB.
My, how technology has advanced!

Thanks for all your comments.
I will certainly look into cleaning the system out and checking for dry caps - a very good idea.
Sadly, we dont have pythons or boas in this country to deal with rats.

Tracking powder works very well...

John

Hi azecraze,
This is a real blast from the past.
I worked with Fanuc NC controllers in the early 1970's.
McPhersons research division in Melbourne developed several standard and special purpose NC machine tools. Later we developed BTR DNC and I worked in UK developing a Digital PDP-11 computer based CNC controller for lathes.

To your problems. Firstly, keep the rats out. Secondly, BTR is very simple but it must emulate the operation of the paper tape very precisely. You must get the data transfer rate same as the tape and the paper tape sprocket hole is usually read and used as a sync pulse to transfer the data. The Fanuc hardware was always of very high quality (for its day) with very few failures.

If you have the equipment I would try to revert to use of paper tape to try to prove whether your problems lie within the BTR or the Fanuc controller.

Good luck with it.

Personally what I would do is go to E-bay and do a search for a Fanuc 0-m control. You should be able to pick one up for a pretty reasonable price, and then do a complete retrofit on the machine and be done with your problems for good. With the money you save in downtime it would pay for itself very quickly.