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Monarch 10EE Modular Drive Dead?

jgnichol

Plastic
Joined
Feb 3, 2015
Hey all,

Our 1964 10EE died this week. This is a modular drive machine. After spending a couple of hours running tests and sifting through the wiring diagrams Monarch provided for this machine (best money ever spent, buying the manual and schematics from Monarch) I'm stumped.

Here's what I've tried. With the module in and the speed control turned all the way up, the lathe will rotate at perhaps 150 RPM. It's the same forward as reverse. With the reverse speed control full up we get the same speed, 150RPM, just in the opposite direction. This showed up after a couple of hours of heavy machining, but not immediately after -- the next day.

With the module out, we get something like 3000+ RPM (don't like to let it run too long like this, so I don't know where it would have settled out). I checked every component in the module. Diodes, resistors, capacitors all check good and have the correct values.

I've traded out the tubes, to no effect. The fuses are good.

Any suggestion what to try next?

Thanks all.
 
If the speed settles anywhere near 2K RPM with the module out it's very likely the problem is in one or more of the diodes in the module (the other module components are not usually stressed). Here's a thread that gets into making diode replacements:

http://www.practicalmachinist.com/vb/monarch-lathes/blowing-diodes-my-10ee-221945/

rke[pler, thanks for pointing out this thread. The diodes all test good with a multimeter (could they test ok and still not perform correctly?).

I'll check the speed control potentiometer next.
 
Double check the spring clips that hold the diodes in place. They can cause some grief.

I had trouble with my potentiometer. With the machine on, I tapped the pot with the butt end of a screwdriver and the machine would surge.

Hal
 
Glad you found monarch central help (You called me about this issue).
As noted above the diodes - and slightly flaky contact on diode connections - can cause issues. If you follow the treads you can replace them all with a couple dollars worth of modern diodes and make carriers.

The dual pot for speed control have also been known to fail - I seem to remember the last person that reported buying one from Monarch the price was ~$125???

The people here will help debug - they know far more of the drive details than I do.
Paul

(at least I'm assuming it was you that called me otherwise there are two machines like this currently in MA)
 
(at least I'm assuming it was you that called me otherwise there are two machines like this currently in MA)

PaulM,

Seems like there is a plague of Monarch diode disease spreading across the state. I don't remember that we talked.

Hope to have time to do more checking later in the week. Lots going on here now (thankfully).

Take care.
 
I had trouble with my potentiometer. With the machine on, I tapped the pot with the butt end of a screwdriver and the machine would surge.

Hal

Hal,

Had a bit more time to work on this. Tested the potentiometers. They test good. In-circuit the 50K potentiometer reads about 26K across the outside terminals. Both wipers move across and generate the correct resistance range.

Should have known it wasn't the potentiometer because it behaves the same in forward and reverse -- slow 150RPM top speed, no torque.

Did another test. Took the chuck off and unplugged the control module. When I power up the lathe and engage forward drive with the module removed, the spindle speed surges initially to about 3500RPM for a few seconds before settling in at about 2700RPM.

Perplexed. Any ideas about what else to check?

Thanks for your help.
 
Try measuring the armature and field voltage across the speed range. You should see the armature vary from 0-240/250 through the first half of the speed range while the field remains constant about 120. The second half should see the armature stay constant while the file goes from 120 down to 25 or so.
 
Try measuring the armature and field voltage across the speed range. You should see the armature vary from 0-240/250 through the first half of the speed range while the field remains constant about 120. The second half should see the armature stay constant while the file goes from 120 down to 25 or so.

Finally found some time to spend on this. At the low speed (module installed, max speed setting, ~100rpm), the motor field measures 13vdc, the armature measures 9.8vdc. At high speed (module removed, ~2700rpm) the motor field measures 27vdc and the armature measures 222vdc.

Does this seem to you like a bad module? Seems like everything points that direction (pic below). Every component in the module (except the supressors -- not tested) test good. Is is possible a diode will test good with a multimeter but not work right under load?

Spent some quality time with the manual scratching my head. Can't figure out what else it might be.

Thanks for your help.

IMG_1120.jpg
 
Hal,

Checked the potentiometer. It seems OK. I was surprised to see that the speed control potentiometers in my lathe are the stamped metal casing type. Kind of like a 1960's stereo. I would have expected some over-the-top wire wound instrumentation-grade potentiometer of some sort. You have something nicer in your lathe now?
 
Finally found some time to spend on this. At the low speed (module installed, max speed setting, ~100rpm), the motor field measures 13vdc, the armature measures 9.8vdc. At high speed (module removed, ~2700rpm) the motor field measures 27vdc and the armature measures 222vdc.

Does this seem to you like a bad module? Seems like everything points that direction (pic below). Every component in the module (except the supressors -- not tested) test good. Is is possible a diode will test good with a multimeter but not work right under load?

Spent some quality time with the manual scratching my head. Can't figure out what else it might be.

Thanks for your help.
View attachment 183011
Yep it can check good at low voltage (multimeter) but act like a zener diode at higher voltages conducting both directions.
 
Finally found some time to spend on this. At the low speed (module installed, max speed setting, ~100rpm), the motor field measures 13vdc, the armature measures 9.8vdc. At high speed (module removed, ~2700rpm) the motor field measures 27vdc and the armature measures 222vdc.

That sounds like there's something wonky in the field, mostly likely the C3J (the smaller tube). That's the most likely failure, anyway.

(Anyone else having trouble entering space charactgers in a reply?)
 
Almost, but not quite a diode problem. Maybe T4.

Thought for a second I had this. Removed all the diodes from the speed control. Tested them using a (small 12V)lightbulb and power supply, as suggested here:

1EE Journal - Page 8

I was delighted to find that one of the diodes was open in both directions. Made up a replacement by hollowing out the defective diode, and fitting a 1N5406 inside only to find that the "new" diode didn't solve the problem.

Diode swap out was easy. Unsoldered each end of the diode, slid the housing open, removed the old diode, drilled out the ends to fit the larger diode wire, sanded them down a bit on the belt sander to save some space inside (wouldn't have to if I'd had a physically smaller diode on hand), reassembled, re-soldered, done. Left a small gap for thermal expansion differences. A few pics of the diode swap-out:

IMG_1128.jpgIMG_1129.jpgIMG_1130.jpgIMG_1131.jpgIMG_1123.jpg

After more checking it looks like Transformer T4 isn't working. Primary voltage is fine. Secondary voltage is about 35VAC, should be closer to 270VAC. Anyone have any luck rewinding a constant-voltage transformer? Any hope that is something else?
 
Labeeman,

You nailed it. A new capacitor and the 10EE is back in business.

Thanks a ton to everyone who offered suggestions, pointed out threads and asked questions. Cheers all.
 
Labeeman,

You nailed it. A new capacitor and the 10EE is back in business.

Thanks a ton to everyone who offered suggestions, pointed out threads and asked questions. Cheers all.
Glad It helped get you up and running You are welcome.
 








 
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