yet another 10EE controller problem

Folks,

I'm brand new to the board and am quite interested in learning about machine work of all sorts. I'm an electrical engineer specializing in electronics (aerospace related) and am trying to help a good friend get his 10EE lathe running. The controller has two (C16J) thyratrons as well as one C3J thyratron. Symptoms are that the controller seems to be operating more or less normally upon power up until the control lever is moved into either the forward or reverse position. If the speed control is set to minimum, nothing untoward will happen, but if the speed control is advanced slowly, a very loud buzzing and vibrating sound occurs. The spindle will attempt to rotate, but only a few degrees. Since we live about a thousand miles apart, I'm forced into a sort of long distance troubleshooting routine and could use a little help with this. So far, we've replaced one of the C16J's since it was rattling somewhat when shaken and was not igniting. At this point, I speculate a short of some sort in the wiring, but am having a bit of trouble in verifying this as well as tracking the basic problem down. Motor series and shunt fields appear to be ok as well as the various connections to the thyratrons. Everywhere I've had my friend check seems to be in fairly good shape. We've measured voltages in the field control section, reference voltage section as well as the phase shift section...based on what little I know about these particular controllers, the voltage measurements seem to be about right...or at least not catastrophic. I certainly would appreciate any suggestions you folks might have in the way of ruling out various sections of the controller or other troubleshooting tips you might want to offer.

Thanks,
JR

Can we assume you mean the spindle turns at minimum speed? Or does it stay motionless until turned up?

And is this indeed the one with ONLY the three tubes, no other ones? With just one field tube that should be it.

At two removes trouble-shooting is even poorer, but what the hey.....

The buzzing and vibrating sounds very much as if the DC motor was getting a poor grade of DC, with a lot of ripple and a low average current.

Motor normally will get more or less truncated half-sines, full-wave rectified. It sounds like there might be a problem that is causing half-wave only. That in itself might not be so bad, but whatever is causing that is probably also fouling up the grid drive so the remaining working tube isn't getting good drive.

Or, the grid drive transformer might just be reversed in phase, in which case it will drive poorly if at all. The turn-on will occur with reversed polarity on the tube.

or as you mention, the grid circuit might be fouled up.

Or the speed control circuit might be poorly filtered and giving ripply DC to the speed pot.

If you remember that the tubes act as SCRs do, but with a larger reverse voltage allowed on the grid than an SCR permits, you may get further.

That particular style of control seems to work by the whole grid drive "walking" up and down in voltage due to grid rectification, so if anything is wrong with one tube, the voltages are all fouled up.

Somewhere I have the files for the circuit to that model that were sent to me by someone. If you don't have them, let me know.

I think they are also posted, possibly on the metalworking "dropbox" at the rec.crafts.metalworking site.

This is a "Modular" drive.

The armature (and, implicitly, the series field) is supplied with up to 230 volts dc from a full-wave rectifier (2 x C16J). About 18 amps for a 5 HP machine; somewhat less for a 3 HP machine.

The (shunt) field is supplied with up to 115 volts dc from a half-wave rectifier (1 x C3J). About 2 amps.

Up to about 50 percent rotation of the speed control, the shunt field voltage is maximum; above about 50 percent rotation the field voltage is intentionally reduced ("field crossover"/"field weakening").

The motor itself inherently acts as a low-pass filter on the output of each power supply, the outputs of which are actually pulsating dc.

Failure in the pulse forming section could account for C16J misfires. A single transformer and one pulse former for each grid (basically low-pass filters, perhaps acting as "sample and hold" functions).

Poor/burned contacts in the control box could account for failure to start.



[This message has been edited by peterh5322 (edited 03-11-2003).]

remove the module box and power up the lathe engage the spindle start lever and see if the lathe runs at base speed about 2400 rpm. If does the problem is in the module.

Yes, this is a controller with only 3 tubes involved...all else is either semiconductor, caps, resistors, or inductors. Yes, the spindle does remain motionless until the speed control is somewhat advanced....then vibrating sound occurs and spindle attempts to move a few degrees, but stops.

Looks like first order of business is to remove the module and rule out a portion of the circuitry. Will try and get this done and go from there.

Thank you very much,
JR

Check the speed control.

It's in a sealed cast aluminum box which is connected to the drive through a liquid-tight conduit.

There are two pots in there, in tandem.

One controls the armature (and series field) voltage; the other controls the (shunt) field voltage.

Intrusion of oil into this pot, which is not hermetically sealed, unlike all the other pots in the drive, can contribute to erratic operation, or to non-operation.

Pull the black module box--inside is a bank of about 10 diodes--check all of these--Monarch has replacements for about $5 each--also, there are two pot adjustments on the black module box for speed and braking--try adjusting these pots--check the manual--in the back is the recommended filament voltage for the two rectifier tubes--there are multiple taps for each transformer at the base of the rectifier tubes and the right tap needs to be selected for the suggested filament voltage

I forgot,also check to make sure the multi-pin connector for the black control module is making good contact on all pins as this will cause erratic operation--contact for more info as I have the same controller

Ok Guys,

I had my friend remove the module and give it a try....still no spindle motion. I'll have him post here as well since he probably can be a little clearer about what is going on up there in the far north.

JR

Gentlemen:

Here I am, reporting from the Great White North. I am the one with the controller problems that Mr. alterfurz posted about. My knowledge of what electrons do is pretty limited. I know that they are really fast and you cannot see them.

A semi brief history of the problem:

I used to run this machine in a shop, and managed to get it when the powers that be decided to get rid of it. It seems to me that there were some small drive problems with it when it was still in service. If memory serves the spindle slow down/ braking was not functioning.

It is now in my basement and being fed 220v single phase. I made all appropriate changes per the manual to run it on 220, with the exception of the high speed test readings, because I was not able to get the high spindle speeds. Range was from 0 to 1K. This is a 4K machine.

The rpm limitation was not a problem for what I do so I more or less ignored the problem. Recently it began to misbehave. The spindle would not rotate when the lever was put into forward. If put back to neutral and then shifted it would start. Or maybe not. The problem got worse until it would no longer start.

Well, I must confess that I was a mechanic in a previous life. Falling back on my old training, I hit the control cabinet with the meat of my hand. The spindle immediately started and worked like a charm for a couple of weeks. Then it quit. Subsequent hitting did not help. <g>

I don't recall the exact history here, but when the lathe finally gave up completely, we discovered that the diodes in REC2 were bad and replaced them. When the machine was powered up and shifted into forward it ate the diodes again, along with FU1. After going through a couple times, and checking a bunch of things Mr. A suggested I swapped the two CJ16s (put each in the other's place) and that is when the buzzing started. It was also when I discovered that there were pieces of metal rattling around in one of the tubes.

Now when the lever is shifted into forward, the spindle moves a few degrees and then a hellacious buzzing noise comes from the control panel and/ or the motor. I believe it is from the control circuitry. If the the speed control potentiometer is turn all the way to zero nothing happens, which is how the machine always operated. As the speed pot is turn up a bit the spindle just starts to turn and then the buzzing begins. If left for a few seconds it will trip the main breaker.

The rattling tube was replaced with with no noticeable change in the symptoms.

I just tried running the spindle without the control box as suggested here. Nothing. No spindle rotation and no noise. I tried it several times and once the spindle did rotate a few degrees, but otherwise there was not reaction at all to the shift lever.

I apologize for the wordy post, but I don't have the knowledge to separate the wheat from the chaff. My sincere thanks in advance for your consideration of this problem. It is a wonderful machine and I really need it to work.

Respectfully,

Glenn

[This message has been edited by hst (edited 03-11-2003).]

GReat data! Perfect explanation of problem.

Ok, the dead rectifier is part of the "fixed bias circuit", which works with the speed control to set your speed. There is a voltage produced which is added with the speed pot output and the current compensation to get the voltage setting for speed.

If it was not producing sufficient voltage, it would probably never get to high speed. This is what you were seeing, so that sounds likely.

It might not produce enough voltage to get very far out of the area where intermittent firing of the thyratron tubes might be experienced. That might cause the vibration and weak rotation.

Now, is the rec 2 problem (blowing rectifiers) still there? if so check Supressor #2, which may be shorted. There isn't very much else except a wire with worn insulation that could cause that problem.

BTW, the fuses also feed the speed pot circuit (reference voltage) so lots of stuff won't work if they are blown.

Also, the other fuse, FU4 might be bad and not look bad.

I think your problem is in the speed control. You might have found a crummy tube, but that doesn't sound like the main problem from what you posted.


I sent you schematics, emailed 2 PDF files. I could not send to your engineer friend, as his email wasn't available. They are kinda big, might take a while to receive. If I had any sense I would have sent them one at a time.

Mr. Tiers:

Thank you for the reply and for the prints. They down loaded without difficulty. The prints are the same as the ones I have, and that Alterfurz has a copy of. The one exception that I know of is that I have no FU4 in this machine. Instead of the two 2.25A fuses there is one 5A fuse in the place of FU1. We now know for sure that we are talking about the same controller.

>>>>> Now, is the rec 2 problem (blowing rectifiers) still there? <<<<<

No, that problem seems to have gone away. I did indeed find some wires that had the fabric insulation compromised and taped them up. I forgot to mention this in the first post. This may well have been the problem eating the diodes and FU1. I intend to replace that fabric insulated wiring with a suitable heat resistant wire when I am convinced the controller can be saved.


>>>> Also, the other fuse, FU4 might be bad and not look bad.<<<

I have only FU1 and FU3, and both are good.

>>>>> I think your problem is in the speed control. You might have found a crummy tube, but that doesn't sound like the main problem from what you posted.<<<<<

Since the current problem arose when I swapped tubes, I rechecked the wiring on them and found it to be correct. I put the original tubes back in their original positions and the problem remained the same.

Thank you for your help. Any ideas you can offer I will explore to the best of my ability.

Respectfully,

Glenn

Well, that does change things a little, you found a possible cause for the rectifier problem. It is always good to find a cause for any problem, that way you can feel more sure its fixed.

At this point, what about voltages? You mentioned that all the voltages looked OK, does that include all the ones in the table at top left? (leaving aside the high speed ones).

Also, see the note on shunting the current transformers differently for 230 and 460, which is down just above the "FIGURE 12" in the title. Since you have more current flow at 230, the compensation must be reduced. That could lead to instability if not done.

Note that none of these issues we discussed has to be the full problem, just that if there was an original problem, changing to 230V might have involved doing something that changes the way the problem appears.

There is also a suggestion that something is loose, due to the fact it improved when hit. That suggests going over everything for more worn insulation or loose connections, wires broken inside the insulation, etc.
(Of course your hitting it might just have dislodged the wire you already fixed so it wasn't touching the case any more!)

Sounds like some work with an ohmmeter is in order, checking continuity of wires, and making sure they don't short to the metal chassis.

It's hard not being on the spot, since many of the possible ideas could be eliminated by a quick question, or a quick look at something.
In our situation, it takes a posting exchange to deal with them. So 10 minutes work may take 24 hours time. Hopefully this isn't too frustrating.

I have done quite a bit of searching for shorts and loose connections, but I will go over it all again. I will start disconnecting wires and checking continuity.

I did change the shunting as described on the print by compensation circuit for operation on 230v. I will check it again.

About the voltage readings. The chart indicates reading at 200 and 2000 rpm. I have no spindle rotation and if I try to get it to rotate the chaos begins. What condition should I have the lathe in to take the voltage readings? I can power it up and shift it into forward as long as the speed control pot is turned all the way down.

Thanks again,

Glenn

[This message has been edited by hst (edited 03-12-2003).]

Good afternoon:

I took the trusty ohmmeter to the wiring again. Actually, the meter seems to be giving some strange readings, such as the ohm meter scales not correlating when switching from one to the other. I think that the purchase of a good meter is in order. Still, it works well enough for continuity tests.

I checked the continuity of all the wires from the two terminal strips on the control board (the board that the tubes are mounted on) to the terminal strips in the main panel. I also checked them to the module plug where applicable and all showed continuity. I did not remove the wires from the strips to check, so in some cases I reckon the current could be taking an alternate path.

I also check these and all points on all terminal strips to ground. No problem there.

I checked again the diodes in the module and all appears well. I did not check the suppressors as I was not able to identify them. What do they look like and how are they checked?

Thanks, Glenn

The suppresors are round Bakelite assemblies, perhaps 1-1/2" in diameter and perhaps 1" thick.

These may be labeled "GE" and "Thyrite".

These are simply voltage variable resistors, somewhat similar to the MOVs which are currently used in 'puter surge suppressors.

I find nothing that meets that description. I have found two things inside the 'black box" that I cannot identify. They are assembled stacks of 1" square wafers with two round 1" diameter disks on each end of the stack. From one end to the other, there are two round disks, some small spacers, a number of squares, some kind of round spacer, an equal number of squares, a spacer and two round disks. They are painted gray and when scratched the squares seem to be aluminum but the rounds are something else.

The numbers on the units are 6RS21SA13D13 and 6RS21SA5D5 and both carry the GE logo. The 13 and the 5 seem to represent the number of square disks in each stack. The tall one is about 1.5" long and the other perhaps 1.0".

The ohm meter showed infinite resistance in each direction on one stack, but the other showed some current flow in one direction only. This would not seem to be a good thing.

Glenn

What you're describing are selenium rectifiers, not Thyrites

Good for low, but not high voltages, and for low, but not high currents.

Usually replaceable by silicon diodes.

Without looking at the schematic diagram for the "Modular" drive, I'd guess that the rectifiers you described were in the "reference" circuit.

In this model drive, the armature (and series field) and (shunt) field rectifiers, both of which are high voltage and high current, relatively speaking, are Thyratrons.

I may have missed this--was your machine originally 440/460--mine is and in my initial setup I found that all transformers in the lathe could be re-tapped for 220 operation except the two transformers located at the base of the rectifier tubes[I don't have the schematic in front of me so this is from memory]--unless your control setup is different than mine these must be replaced with transformers appropriate for 220v--because the cost was so high I left everything as is and ran single phase 220 into a stepup transformer and now run on single phase 460--to make a long story short make sure all your transformers are delivering the correct voltage based on the line voltage you are using--otherwise, It sounds like you may still have a bad tube or a shorted wire somewhere

Hmmmmm...... That is true on most if not all......didn't consider that.

I don't have a clue if it would work at all on 220, which is about half voltage, or 1 1/4 volts instead of the 2 1/2 for the thyratron filaments. I DO know it would be bad for them to run it very much at that condition...

Sounds like something to be sure of, as you DID say you re-wired to 220.