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New video of fried out CX700 lathe problems

DPittman

DPittman

Ultra Member
Below is an updated version of my troubles, hopefully I don"t get others as confused as I am. I forgot to mention in the video that I tried 12 volt power to my dc motor and it seemed to work fine both forward and reverse.

Don

 
What is the fuse (that blows persistently) wired to? (both schematically & in real life)

When the lathe zonked, was it during actual cutting, or when a switch was thrown on/off?

When you temporarily rigged power to the motor, does it just turn or will it spin to full rpm? (not sure that's possible to check safely without the speed control thingy in line, but just a thought).
There are diagnostics for checking motors across various windings, but above my pay grade.

I think its worth examining those switches too. If there is a partial or intermittent short for whatever reason, then current can go where it doesn't belong. Is it relatively easy to pull them out a bit to examine the wiring connections? Ideally remove switch altogether & test contacts with continuity meter? If you see loose tabs, melted plastic or evidence of magic smoke that would be suspicious.
 
Thanks again Peter for your advice. I think I will try things with the motor not connected....see if that blows a fuse.
Yes the lathe zonked out during a cut, I believe it was during a stall, and I think I blew a fuse also but don't remember if that was the front or the back one.
I will check tomorrow how exactly that fuse is wired.
I only hooked up 12 volts to the motor from a vehicle battery and am assuming it got to the speed 12 volts would have allowed. It went both foward and reverse without any obvious trouble. The motor is 90 volt dc.

There is no sign of electrical failures in any of the wires or switches that I can see but I have not tested the on off switch yet.

The last electrical component I haven't yet replaced (except motor) is the on/off switch. I am hoping that it is that maybe but doubtful. I am hoping I can find that part somewhere a little sooner than the Busy Bee route.

Getting parts from Busy Bee takes 3-4 months on a good day. I had paid an extra $50 to get the circuit boards airmailed over but that still took over a month. I've heard of slow boats from China but not slow jet planes?!?

This is all also WAY above my pay grade!

Don
 
Ive had all sorts of switches both new and gently used fail, most especially ones with 4 wires
 
I've had my craftex mill die before my son was taking a heavy cut and the donut looking thing got hot enough to desolder and fall onto the board below bb gave me another ( but different ) board that worked but the rpm readout has never worked since. On another occasion the motor would hunt the (brushes are a weak point ) the front one was fine but the rear one was toast basically came out broken, another problem was getting the Bastard out it seems that by heating up it fuses the brush with the cap destroying the brush when (if) you remove it eventually I sent the motor back for a replacement and ordered a spare for the future! I belive I solved the brush problem by cutting brass shims to fit the inside of the brush cap.
 
If I understand your test, 12v battery was connected direct to motor terminals & it ran ok? Its logical that it would be lower rpm because its capable of higher range. Then maybe it worked because battery voltage bypassed something like a transformer between HV source & motor & that's what's fried? ie, when you power up conventionally, that part is once again in the circuit? Maybe there is a test to can check resistance across windings? However, this doesn't quite explain different results by swapping the new/old control boards though, presuming they would send control signal to that transformer? Listen to me, Mr. BS electrician :)
 
My crafted mill did something similar, turned out to be a faulty safety switch -- locking if the off position. Damn thing had power everywhere but wouldn't start . Bypassed that switch and she fired up. Likely not your issue though


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Does it blow the fuse as soon as you plug it in or after the main power switch is turned on or after the forward/reverse switch is move from it's middle neutral position? Fuse 1 protects all the circuits but fuse 2 only protects the motor. Which one blows?

 
I doubt that on off switch is your problem. Did you replace the forward and reverse switch at the same time you replaced the other 2 boards? I'd go through that schematic with a multimeter and see what you get for power.
The main thing is do is pull the leads off the NEW speed control board at the A+ and A- and then turn the machine off but check the DC voltage there. If you're seeing voltage then try plugging the motor right into it without the switch and see if you can bring the speed up and down.
 
To answer some questions.. The fuse blows as soon as I hit the main power switch on, it doesn't seem to matter which position the reverse/forward switch is in. It is fuse 1 that blows.
I tried disconnecting the motor completely and the fuse still blows, so o think that means its not my motor.
I think im going to take the circuit boards into a place in Lethbridge for testing.

Ive replaced components with several different combinations now so it might be possible that I've fried new previously good components.

Man I just wanna turn some metal.
Don
 
Looking at the schematic my next step would be to disconnect the reverse/forward switch and see if it still blows the fuse. I'm not sure why but there is some switches in the A/C part of the circuit in there. The "filter" board looks like it rectifies the A/C to D/C. If it still blows with the r/f unhooked I'd disconnect the filter board next. There is something weird about the schematic as it shows the neutral (terminal 14 at main switch) get connected to line power after the filter board if switch terminals 9-10 are closed. That would be a dead short between line and neutral I think.
 
What if Don buys a variable voltage and current bench or lab type power supply suitable for the dc motor specs? You could bypass nearly all busy bee parts and run the motor directly I think? Not sure about the cost but doable?
 
Ok here's something I learnt that was a huge surprise to me....

The speed control circuit board in my Busy Bee Craftex lathe is a common, USA built speed control board used in many applications!!!!! This is what I was told by the staff at the electrical shop I took the boards to for testing. (and now I can see the branding right on the board myself)

Also I just found suspicious smushed wiring for a tiny little led indicator light that certainly was not right. I fixed that issue but don't know if that existed earlier or if I just recently smushed it with my monkeying around.

Don
 
I suspect it is the same common speed control board used in treadmills. Most of them also use a 90 volt dc motor.
 
"Kb electronics" out of Florida is the name on the board and after a quick search I see it has been used with some lathe variable speed retrofits.

Don
 
Good lord man that looks easy and nice. I wonder is it could possibly be that easy AND CHEAP!?!

I gotta investigate....

Don
 
You would probably still need to use the existing forward/reverse switch to get reverse but that would be easy enough.
 
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