Strange slow fail on my Modular - Page 2

# Thread: Strange slow fail on my Modular

1. Aluminum
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280 out of gear
56 in gear
I thought those were the leads you were talking about but I just wanted to make sure.

2. Aluminum
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Originally Posted by mllud22
Check through pages 10 through 19. Its a pdf file of the manual. The electrical section is pretty good.

http://www.vintagemachinery.org/pubs/2103/3423.pdf

Thanks for the Download,I've got the manual from Monarch for my machine but having an ecopy is great.

3. Cast Iron
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Originally Posted by Drstrangelove
280 out of gear
56 in gear
I thought those were the leads you were talking about but I just wanted to make sure.
You will need to find what is loading that circuit down when in gear. Check the primary of t4 when in gear and see if it is 240 VAC

4. Aluminum
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Originally Posted by labeeman
You will need to find what is loading that circuit down when in gear. Check the primary of t4 when in gear and see if it is 240 VAC
So the primary of T4 (33 and 66) is 125VAC both in and out of gear. That checks with points 1 and 2 which is the control voltage.

5. Cast Iron
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Originally Posted by Drstrangelove
So the primary of T4 (33 and 66) is 125VAC both in and out of gear. That checks with points 1 and 2 which is the control voltage.
OK something is loading the output of T4 when it is in gear T4 is a constant voltage transformer cant be to constant if it changes to 55 volts when in gear versus not in gear. Check the field voltage on the spindle motor when in gear and not in gear it should be 100+ dc at the lowest speed setting lets see if that is working.

6. Aluminum
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Ok so I realized that I had disconnected the incorrect leads this morning and rechecked the T4 secondary voltage with 47 and 48 disconnected. Same outcome, T4 secondary low, 56 ish volts but the lathe momentarily spun up at full acceleration before the QSD kicked in and stopped it.

Measuring from pin S1 to S2 on the terminal strip below the main contactor I got 0VDC out of gear and 70MVdc in gear.

7. Cast Iron
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Originally Posted by Drstrangelove
Ok so I realized that I had disconnected the incorrect leads this morning and rechecked the T4 secondary voltage with 47 and 48 disconnected. Same outcome, T4 secondary low, 56 ish volts but the lathe momentarily spun up at full acceleration before the QSD kicked in and stopped it.

Measuring from pin S1 to S2 on the terminal strip below the main contactor I got 0VDC out of gear and 70MVdc in gear.
Nope F1 F2 shunt field is what I need for you to check.

Delta is going to visit me tomorrow and I may not be able to communicate for some time.

8. Aluminum
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128VDC out of gear
74VDC in gear

I have to have the speed knob turned up to about 1/4 speed to get the spindle to rotate.

9. Cast Iron
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Originally Posted by Drstrangelove
128VDC out of gear
74VDC in gear

I have to have the speed knob turned up to about 1/4 speed to get the spindle to rotate.
You do not need the spindle to rotate. You need to find why the reference circuit is dropping down so much when you engage the spindle fix that and your problems will go away. I suspect you have a chip that has shorted something I would take the modular out and blow it out you have a short you need to find. It sounds like it went away for a second for you.

10. Aluminum
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Good to see you back.

I'll do that today, I've had the modular cover off a few times checking voltages but I'll give it a blow off.

I'll also recheck the shunt field voltage at slow speed.

The full speed acceleration I saw was due to the control or grid lead's being disconnected from the SCR's. With those disconnected the speed control and the constant voltage transformer voltage aren't part of the functional circuit. I spent a lot of time looking at the schematic after that and understand a tiny bit more how this thing functions. Digging back to high school electronics and the little bit of tube experience I have building a guitar amp. Still way over my head though.

11. Aluminum
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Ok, finally got out to the shop.

It shows 125VDC across F1-F2 at slow speed position on the speed knob.

Blew out the Module and no change.

12. Cast Iron
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That is correct it should only go down when the pot is at half turn.

13. Aluminum
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Ok, I checked that and that is what happens. 125VDC until about half rotation of the speed knob then the field voltage starts to drop off.

14. Cast Iron
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Is your reference voltage still dropping voltage when engaging the spindle? Your field voltage circuit is working fine now.

15. Aluminum
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Yes reference voltage is 280 out of gear and about 55VAC in gear. I tried it with the speed knob all the way slow which typically has no spindle motion and still 55VAC.

16. Cast Iron
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You have something loading down your reference that is not supposed to happen you have a short some where and until it is found the drive will not work right.

17. Diamond
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Originally Posted by labeeman
You have something loading down your reference that is not supposed to happen you have a short some where and until it is found the drive will not work right.
Not my area of expertise, but "hollow state" in general has been, Not necessarily a dead-short. Resistance path where none was meant to be, perhaps a capacitor that has perished, or a carbon-trail built-up of soot and biologicals or metal fines gone rogue. It may, in other words, be failed-component OBVIOUS, or it may be near-as-dammit invisible to an ordinary inspection.

But yer right.

It is "there somewhere", and detective work to FIND it must be put on the tasking list.
Twiddling knobs ain't good enough to make it volunteer to undo itself.

This stuff isn't "magical". Not as if it were a height-finder radar set, Lenkurt mux, or an FPTS rig.

Fair SIMPLE, a thyratron DC drive, actually. But it CAN be tedious.

18. Aluminum
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Understood, any recommendations on a path through the system or just pick a wire and start following it? Also would pulling the module and running it help me isolate a particular area of the circuit?

I'll be heading to training for a new job at the end of this week and will be out of contact for a couple months probably. Other side of the country and all. If i track it down before i leave i'll let you know otherwise it'll be a while!

19. Cast Iron
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Disconnect wires on the scr side of the speed pot not on the field control side

20. Aluminum
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I disconnected the speed pot at point 36 and tried to run it. When I engaged it in fwd the C3J tube dimmed then the master contactor disconnected. Spindle turned briefly.