BP Series 1 Z-axis problem (BOSS 4)

[ABT]

Hello everyone,

I recently bought a BP Series1 CNC with a BOSS4 control.
It only has one problem, the z-axis is not working correct (only small steps).

I've read a lot on this forum and it showed to be a standard problem of these machines.

The only difference is that I read nowhere that a resistor on the SMS board is blown, normaly it's a transistor that's broken.

I've a picture of it so it's clear.

Now I've couple questions:

-What caused this blown resistor ?
-What else is possibly broken ?
-How can I check if the transistors are broken ?
-Does anyone have the exact specifications of the mounted steppers, (see inside cover on picture)

I hope someone can help me with this issues.



Aad Boers
Holland

[colin1544]

Hello Aad some years ago I had a series II NC with the type of boards with the large resistors and the failure was due to excessive loading on the Z axis although this had a Knee Z axis but it was run without the air assistance and created constant Z axis loading sorry I cant help with spec on the stepper motor I have a spare one if you need one Cheers Colin

[machintek]

This is very common. Typically there is a failure of the Ceramic resistor on the Saturable Core Reactor. This in turn blows the correspoding fuse on the SMS, typically blows the resistor and typically melts the solder out from underneath the corresponding large transistor on the ACC.
I usually replace the resisitors on the SCR with ones of the same value but twice the watt capacity. I used to buy them at Radio Shack.

George

[ABT]

Thanks a lot for the info !

Are besides the resistors you mentioned, the transistor also damaged, or only been very hot.
And where is the watt capacity mentioned of the resistors, I can't see it (on the picture)


Somebody info about the specs of the steppermotors ?
I need it to look for the possibiliy of changing the drives to new one's and use Mach3 controls

[machintek]

when the resistors are failing on the SCRs (Saturable Core Reactors), they show cracks on the bottom. These are 5 watt devices. I replace them with 10 watt devices because they can dissipate the heat better.
The SMS already has 10 watt resistors. I replace those with the same wattage pieces. I cannot tell you if the ACC is still good, but you can flip it upside down and then that portion of the board will regulate the current on the X axis instead of the Z.

George

[bbuonomo]

Z axis failure is very common, when you rapid Z up and it "crashes".

Here is the tread that i posted a while back, with some great advice and lots of diagnostic info. Good luck.

http://www.cnczone.com/forums/showthread.php?t=25797


Brian