Another failed G0704 motor controller

[LUCKY13]

The brushes look like they are better in the new motor, the wire in them are copper instead of whatever the other ones are. Plus the springs like like they are better.


The old motor looks like it has a capasitor in the line, the new motor doesnt look like there is anything there.


I wouldnt remeove the fan, just add the outside fan.



I bet when the motor got some heat in it that the brushes where not making good contact. I cant remember who it was that posted but the motor didnt want to run smooth with the battery charger. This is a good sign of the brushes not making contact the way they should.


I would order a set of even better brushes for the motor. You can get some nice brushes at Helwigcarbon.com. I would ask them what they say wouldbe best but they have carbon/copper and many other good type brushes that dont cost much compaired to a dead motor. Not only will they last longer, they will perform better and if the right type is gotten they will help the motors connection ring last better. WIth a better connection the motor will put out more power also.


Jess

[photomankc]

Not a G0704, but a PM25... I think I blew the pot as when I turn the mill on - It goes full bore and then trips the breaker. Upon inspection of the control board, nothing appears fried (Scrs or otherwise) - Test the pot and I get out of range readings. Anyone experience a similar issue with the pot on either their G0704 or PM25? Thanks.

My pot was a 'pos' on the PM25 it was shorting out in places early on.

Do note that it is often quite difficult to measure resistance accurately in circuit. If the pot shows out of range over the whole travel then something is wrong either with the tester or the pot. From one leg to the other should measure the full value of the pot. From the middle leg to either end should vary from very low to nearly full value. If not you have a bad pot. You can probably find a workable replacement at any electronic parts shop.

[SgtSpyder]

My apologies to all, I had the inside motor pictures out of order, they’re corrected now.

The windings look like the same size. Can’t really find a good spot to measure the wire thickness.

The old motor brushes are good and had an even contact wear. The blown motor still spins but very slow and will wobble around on the table. Easily pulls 7 to 8 amps on the meter while turning like 50 or 100 rpms. I actually used it to test the current limit pot setting on the on the KBMM-125.

The new motor runs smooth a quiet, not sure of the max rpms. Label says 4300 rpm at 110vdc, I’ll test it in a day or so when I get my digital tach back.

[secutordesign]

My pot was a 'pos' on the PM25 it was shorting out in places early on.

Do note that it is often quite difficult to measure resistance accurately in circuit. If the pot shows out of range over the whole travel then something is wrong either with the tester or the pot. From one leg to the other should measure the full value of the pot. From the middle leg to either end should vary from very low to nearly full value. If not you have a bad pot. You can probably find a workable replacement at any electronic parts shop.

Well I am at a total loss as to what to test for now for where my issue with the controller is... Following your advice, I removed the pot from the circuit and tested - it tested fine I think (5k to zero when turning the pot). I tested the actual feed to the motor (without the motor attached), and it still amps up, blowing fuses (on the machine and at the breaker) - I've checked for visible shorts, and damage on both the controller card and rectifier board, with negative results... Any clue?

[Al_The_Man]

I believe the drive is a KB style that uses an SCR bridge (2 SCR's 2 Rectifiers) with reverse EMF rectifier across the bridge, If it blows on switch on with the motor disconnected the most likely cause is one of the SCR's or bridge components is shorted.
This is the majority of cases I have found when servicing these drives.
The motor can be tested to a great extent by using a 12v automotive battery to check no-load current.
Al.

[SgtSpyder]

The new motor I received is 4300rpm at 110v, after measuring the voltage and the shaft speed the label seems right on what I’m reading. At max voltage ~120v the motor spins at about 4750 rpms

[mdaweb]

A simple test to know if the motor is short or good and simply connect a 12V automotive lamp, the lantern lamps, then the engine turns and the lamp can not flash, it must light linearly if it blinks the engine Is in short, can be seen the test in the following video between the minutes 1:05 and 2:53 follow the video

Greetings,

MDAWEB