[crazyneosimpson]

I am recently employed to run a small machine shop which has an old mori seki lathe with a 5t on it. As this machine slowly failed heading in to winter I noticed the OVC led on the velocity control unit board illuminates when there is a problem, this led is now always on and is preventing the machine from running!
The fuses have been checked and the Z (problem) board was swapped for the X and the led remains on the same board.
Any ideas as to what this means or what I can do about it?
Thanks
Carl

[NC Cams]

The 5T/5M controllers are similar in that they tended to have interconnection problems.

That is, the use of tinned connectors (instead of gold plated) could result in loss of signal to the m/b's. First thing to do is to check, clean, reseat, tighten ALL push on connectors to the M/B, power supply, everything. A cleaning and reseating of any push in IC's wouldn't hurt either. Use care when you R&R them.

There are also instances where the solder on the board to board connector pins starts to deteriourate with age. A careful resolder with the proper rosin core solder may help. THe solder joints should be shiney glossy silver - a flat, dull "spongey" looking one could be deteriourated and you could have ground loop and/or simple resistance problems. The machines don't like that...

Then go thru, check the voltage callibration procedure for the power supply and the mother board. There is also a pot on the A board that adjusts the 5V precision voltage on the a board that does the velocity feedback if memory serves correct. Reseat, tighten, clean, etc all connections.

You have a controller that dates back to the late 1970's - 30 year old cnc hardware THAT RUNS is a rarity anymore. As an owner of 3, I'm happy that mine can even still run.

Unless you toasted something on the board (easy to do if you get a voltage spike or have a loop ground due to a bogus BTR retrofit) simple maintenance may get you back up and running....

[asuratman]

hi,
Do you know the best site to get a used Fanuc controller good and cheap? I am planning to replca my older fanuc with newer one. I saw on ebay, but I do not know what parts I needed. Thanks.

[NC Cams]

"Used controls" "good" and "cheap" are mutually exclusive terms when it comes to Fanuc 5T or 5M controlers as these are late 1970's vintage and clearly "legacy" items to say the least. Documetation is NOT cheap and/easy to find although I do have pristine copys of the OEM manuals.

Fanuc is NOT cheap when it comes to servicing or repairing old "legacy" equipment like this. Frankly, most of the guys who work there probably were not even BORN when these controllers were originally made/sold. I contacted them and got no help whatsoever.

I "lucked" into some used ones that are salvageable from a guy scrapping out some equipment but getting them checked or serviced is NOT a cheap or easy proposition. IMHO, You are gambling with ANYTHING being offered on E-bay and heavy emphasis on the term "gamble".

Glenn Rowe at (972)465-3608 in Irving Texas charges a reasonable fee to test and repair them.

He fixed mine and I paid the normal fees like anybody else. I was well satisfied with the price and quality for ones he serviced for for me a while back. He has several of my boards now and I'm trying to come up with the cash to have them tested/repaired.

Give him a call...

[crazyneosimpson]

Thanks for the quick reply NC CAMS, I believe the maintenence and resoldering dry joints is what the au$1500 bill from fanuc was for! The machine was still running then but not very well.
Does anyone know what the OVC led is for? It is located on the velocity control unit board beside the TGLS led and RV3 Dither trimpot.
Carl

[Dan Fritz]

OVC means "over current". The servo has hit it's current limit and has shut down to protect the SCRs and the motor.

You may want to check the brushes in the motor. Clean out any carbon dust, and check to be sure the brushes are at least 10mm in length. The armature leads to the motor are also contained in a cable that has a MS style connector on the motor. Be sure that the connector isn't full of oil or coolent, which can short the armature leads together.

You may also have a blown SCR, which is equivalent to shorting the motor armature leads together. You can ohm out each SCR separately, but you have to take the servo apart to get at them.

Try disconnecting the armature leads and powering up the control. Does the OVC alarm still come on?

I've got all the Fanuc 5T/5M manuals and schematics, and I used to be a service engineer for General Numeric when the Fanuc 5 was popular.

The common problems on the 5 controls are:

1) Burned connectors on the power supply. The white plastic turns brown, which means that the connector is getting hot. If you see discolored connectors, clean or replace them to prevent voltage loss to the circuit boards.

2) Pratt & Whitney StarTurn lathes had a chuck open/close switch that can short 110 vac to the 24vdc power supply. Be sure that switch doesnt' fill up with coolent!

3) Moving a machine can cause the CNC and/or the servos to run at the wrong voltage. The CNC and the servo transformers have to be "jumpered" to match the line voltage in the shop. A too high or too low voltage to the servos can cause all kinds of trouble.

4) The PC06 hybrid circuits on the "A" board can go bad, causing a servo to occillate badly. These hybrids can be replaced, but they're not easy to find anymore.

5) The servo gain needs to be adjusted on the A board also. There are jumpers and pots for this, but you really need to understand position loop gain settings to get it right.

6) Adjusting these 3-phase full wave servos is complicated, but it can be done with a voltmeter and an ocsilloscope. I don't recommend this for amateurs, but the procedure is clearly documented in the maintenance manual

[crazyneosimpson]

Dan,
This is GOLD I'll check these things out, but you described the root of the problem perfectly with the PC06 hybrids going bad. The original problem is the machine occilating badly then shuting down.
So, how do I identify an PC06 circuit?
It would have been realy nice if the fanuc techie had known this when he was here!
Thanks
Carl

[HillBilly]

I believe this is a PC06.

Darek

[Dan Fritz]

The photo shows another common Fanuc hybrid circuit. The PC06 looks just like that, but with different numbers.

Fanuc 5 controls used 4 hybrid circuits for each axis. In the upper-left corner of the "A" board, you will see 3 horizontal rows of ICs, each row includes:

A-PC01
A-PC02
A-PC03
A-PC04

The PC01, PC02, and PC03 are working together to create the VCMD, or "Velocity Command" signal for the servo. If you put a scope on the VCMD signal and see that it's unstable, the culprit will usually be one of these 3 hybrids. The VCMD signal is visible at a check pin on the A board, or on CH1 on the servo velocity control board.

The PC06 is responsible for creating the "Tach" signal for the servo. Fanuc 5s used a Frequency-to-velocity converter to turn the stream of pulses from the pulse coder into an analog tach signal. The tach signal tells the servo how fast the motor is turning so it can maintain a controlled speed. If the PC06 malfunctions, the tach signal becomes unstable, and the servo goes bananas trying to maintain a steady motor speed. The tach signal is visible on the TSA check pins on the A board, or on CH2 on the servo's velocity control board.

There is also a single A-PC07 IC on the same board, but there is only one of these. It's a voltage regulator that produces a 6vdc "reference" voltage that's used by all three of the A-PC06 ICs. If the PC07 goes out, all 3 axes will go crazy. You can see the +6R, or "reference" voltage at a check pin on the board. It should be a stable +6vdc, and is adjustable with the RV3 pot.

Hint: If you tap on the hybrid with your finger while watching it's output with a scope, you can see the output go bonkers.

[crazyneosimpson]

With your sugestions in hand I started working through the list when I returned to one of the original solutions, warming the machine up! After 5 mins. with the hairdryer I started the machine quickly returned to the velocity control board and sprayed freezer spray on one section at a time until I found that freezing the "LB1287" ic immediatly produced the oscilations giving me grief. So $4 later I have a new one in place, no problems with the freezer spray so I think my problem is fixed I'll do a good soak test as soon as I can. I just hope this thread can help someone else too.

[HillBilly]

Yes, the module I pictured was on the velocity unit itself (found it with freeze spray. It caused vibration when hot.).

I am working on a Mori with a 6M having trouble with the A-PC06. Turn it on Y axis tachloss. After a few minutes of being on reset the servos and all is OK. Got a price on the module (right at $300 but available.).

Darek

[NC Cams]

Follow-up question that sort of pertains to this thread:

My 5T based lathes have Fanuc servos marked: Type 0-2000M.

Does this mean they are Model O's with 2000 line encoders???

The servos are BIG - about the size of a Chevy V-8 starter motor (without the solenoid)

Does any one know the rated voltage, typical current and max surge current specs for the motors???

I measured 65vac/phase going to the velocity units and the 3 phase AC legs have 15 amp fuses/phase. Manual suggests 12 amps continuous current on DC side if I read it right....

Looking to find servo amps that will drive them. The retrofit house claims the motors draw too much current for their drives. They're trying to sell me all new motors and/or monster drives that I'm not in the mood to buy.

These were recently serviced and pronounced "fine/like new".

Thanks....

[Dan Fritz]

Yes, you have Fanuc 0 motors with 2000 line encoders. Almost all Fanuc controls with Analog servos used this motor. Typically, the 0 motor was used for small mills and for the X axis on typical lathes. The Fanuc 5 motor is the same diameter, but a bit longer for more torque. The Fanuc amplifier that powered this motor used 60-65vac as an input, and the 5 motor used about 90-95vac. If you have the servo amplifier also, I would suggest that you used it. It's nicely matched to this motor.

The amplifier/motor combination could be used with almost any CNC control that has an analog output for the velocity signal and pulse coder input for postion feedback. The only problem you might have using this servo/motor combination on a non-Fanuc control is the fact that there is no tach generator. The Fanuc CNC controls would use the pulse coder signals for position feedback, then generate an artificial tach signal for the servo. The tach signal was generated by sampling the pulse frequency from the pulse coders. An F/V (Frequency to Velocity) circuit would generate the 6v per 1000 RPM tach signal for the servo.

[Yabbos]

where do I enter d and h offsets on a 6m I cant find an offset page

[pelletman65]

I'm trying to get this old cnc running. If you have any input I'd greatly appreciate it. The machine has been sitting for 3 years or so. It ran when parked, I replaced the backup battery, the power goes on, panel lights up, but nothing goes on. Programming is still in the NC controller. There are dim red lights on in the back of the cabinet, like old led's. Previous owner thinks that is the problem. Pictures are here showing the lights I hope..

Pratt Whitney Star-Turn 8-15 CNC Lathe pictures by pelletman - Photobucket

Thanks for your help! Dave

[crazyneosimpson]

Ok the first thing I'd check is that bridge rectifier in shot 4 with the red led on, not that I think there's anything wrong with the rectifier, test the voltages in and out of it, AC in ~.6v above the DC out. I don't know what the board should be overall but there are +5v points on the board, they must be within +/-0.5v or there is a problem.
Is LD2 on at the same time as the led on the rectifier or is there a difference? I ask relating to the standard of the capaciters on the board, the one nearest the rectifier is bulging a little but looks intact, however it is one of the things to first check on a partially operating system.
NC controller looks fine, it is now about the external control!