Need Help!- Brpt series 2 Boss 6...Z won't move

[cnc Rookie]

Where do I go from here? I was running a program and in the middle of the program I stopped it with the hold button. (have done this many times before) The Z was down about 3 inches...flipped the mode switch to "set up" and hit the Z zero button.....the Z retracted to about a quarter inch from the limit switch and just stopped BUT the stepper sounded like it kept running for about an extra 5-10 seconds then stopped.
So I pushed the Z zero button again and the same thing....it sounds like the Z stepper is running but nothing is moving. I powered everything down and was able to turn the stepper by hand and get the z to move so i know it isn't a pulley screw. (pulled the bottom cover off and looked to verify this also) If I push the jog button in setup mode the same thing happens. The stepper sounds like it is running but nothing is moving. X and Y are fine so what ever it is...is confined to the Z stepper. When everything is powered up I can not move the stepper by hand so I know it is getting juice to it from the board.
Any idea what to check or where to go from here would be much appreciated.
My next step was going to be replace the stepper with one of the other axis steppers but really didn't want to tear things apart to do that till I could get some other input on what others may think it might be first.
Thanks in advance for any input.

[machintek]

Put the Z in STEP and try stepping it down watching the mechanical counter. If it step down, down, down and then jumps in the opposite direction, you have a shorted transistor in the final drive stage.

George

[cnc Rookie]

It doesn't move at all with any of the controls in any mode. But I can turn the stepper counter freely by hand to make the quill move up and down when it is powered down. When powered up the stepper is holding and will not let you turn it by hand.
I'm wondering if it is a fuse somewhere as it just quit moving after I hit the zero Z. As mentioned it just stopped short of the upper limit switch and showed on the read out that it did zero out. I can move it up and down between limit switches by hand very easily when the power is off so I know it is not binding any where. Thanks
Dave

[jholland1]

In bottom of control cabinet are two control reed relays. The one on left is 24 volts dc power to coil. This is CR1. The one on right is 12 volts . THIS IS CR2.Power for the relays goes thrru terminals 2 and 10. Terminal 2 is at 11 oclock position. Terminal ten at 1 oclock position. Carefully vacuum all chips from both terminals. Move off the wire bail holding relays and wiggle slightly while pulling straight up. Look at top of each relay to verify coil voltage. Next use multimeter and check incomming voltage on pins 2 and ten on both relays. Power for both relays comes from transformers and rectifiers above the card housing in the housing which holds the large capacitors and bridge rectifiers for dc drive power. Your 24 volt power is likely good. The 12 volt supply needs checking before going to next step. With relays out also check all wires attached to terminals.
Let us know what you find.
jh

[cnc Rookie]

Originally Posted by machintek Put the Z in STEP and try stepping it down watching the mechanical counter. If it step down, down, down and then jumps in the opposite direction, you have a shorted transistor in the final drive stage. George

George......
After further review... it is doing exactly this. I watched it a little closer and noticed that at the stepper motor it acts like it is moving for a couple three steps then jumps back. I was watching the quill before and didn't see it moving.
After thinking about what you said I double checked and that's it.
Any idea where I go from here?

Jholland1......
I did check this and believe I checked it right when doing so.....but this is what I found. Just to clarify on my machine the 24v is on the right hand side when looking at it straight down....if you look at upside down it would be the left according to how the writing is on the top of the control reed.
Anyway here's what I found with a volt meter....the 12 volt #2 had 23.4v on it and the #10 had nothing. On the 24v side..the #2 had only 3.94v on it and the #10 had nothing.

Let me know what's next...
Thanks
Dave

[machintek]

You have a shorted final drive transistor (emitter to collector).
They are on 3 aluminum mounting plates, black in color, attached to the right side of the control cabinet. This side opens like a door on hinges to allow better access. The transistor blocks are labeled as per axis and have wire numbers. DO NOT DROP THE SCREWS OR WASHERS! They will land on the terminal strip on the bottom and create a short imitating a shorted transistor. Do not forget the insulator beneath the transistor nor the plastic insulator on the screws.
Bridgeport speced out Motorola 2N6547 as the replacement.
Check the output of T2 to make sure each axis is getting no more than 63VAC or you will blow a lot of these. Make sure DC current is set to no more than 8.0 amps.

George

[jholland1]

Dave
Moderator George is on target. I have a pic of the transistor block in my BP album. http://good-times.webshots.com/album/562583810DfSqiK

BP speced drive transistors at about 15 amps continous at 400 sustained volts. Sounds beefy but the crude switching circuit allowed bad things like emf backfeed on decelaration. The most muscular drive transistor is NTE386. 20 amps continous at 500vdc sus. Current price $18.61 each.
A reliable way to blow a transistor is to hit hold during a rapid axis move. If you continue to use the factory system I will be unloading about 40 lbs smd, acc, transistor blocks on ebay in a few days. Lots of transistors, I just dont know if they are blown.
The above comments are from experienced amateur not EE.

jh

[cnc Rookie]

Originally Posted by machintek You have a shorted final drive transistor (emitter to collector). They are on 3 aluminum mounting plates, black in color, attached to the right side of the control cabinet. This side opens like a door on hinges to allow better access. The transistor blocks are labeled as per axis and have wire numbers. DO NOT DROP THE SCREWS OR WASHERS! They will land on the terminal strip on the bottom and create a short imitating a shorted transistor. Do not forget the insulator beneath the transistor nor the plastic insulator on the screws. Bridgeport speced out Motorola 2N6547 as the replacement. Check the output of T2 to make sure each axis is getting no more than 63VAC or you will blow a lot of these. Make sure DC current is set to no more than 8.0 amps. George

Hey George.....Many Thanks..... It looks as if the plate for the Z is behind the SMD boards. I'll tackle this job on Monday. In the picture jHolland 1 is showing there are 4 of these trans on the back side. Are they all going to be bad or is there some way I can test them? The previous owner obviously had some of the same issues as I found a plastic container strip with 3, what look to be new, extras in it of these 2n6547 inside the cabinet.
Where would I buy more of these at? Would an machine electronics place have them or do I have to go through a BRPT dealer? I'm located in Phoenix area.
Also...you mention checking the output at T2? Could you be a bit more directive as to what this is and how to test for the 63vac and 8amps dc?
I think I can do this now that I finally bought a multimeter today!~! If I don't fry something poking around!

Thanks again...your help is much appreciated......
Learning everyday until I'm done here!
Dave

[cnc Rookie]

Originally Posted by jholland1 Dave Moderator George is on target. I have a pic of the transistor block in my BP album. http://good-times.webshots.com/album/562583810DfSqiK BP speced drive transistors at about 15 amps continous at 400 sustained volts. Sounds beefy but the crude switching circuit allowed bad things like emf backfeed on decelaration. The most muscular drive transistor is NTE386. 20 amps continous at 500vdc sus. Current price $18.61 each. A reliable way to blow a transistor is to hit hold during a rapid axis move. If you continue to use the factory system I will be unloading about 40 lbs smd, acc, transistor blocks on ebay in a few days. Lots of transistors, I just dont know if they are blown. The above comments are from experienced amateur not EE. jh

Thanks for the input and help.
Question...Can the NTE386 be used in place of the 2N6547 and would it be a better fit?

Your right about blowing the trans.........as I think back, the Z may very well have been in a rapid move when I pushed in the hold button. I guess I just been lucky over the last couple years running this machine. I pushed the hold many times over and over and have never had a problem till now. My friend who helped me get the machine up and running told me...."never push the hold button".....he told me to always use the e-stop to stop programs and when I am getting ready to power down ....my problem with that on the programs is my mechanical counter for the X is broke and disassembled off the machine so if I use the e-stop I loose my X0 for the program and have to doink around finding it again.
I got the machine real cheap and use it for my biz but not every day. Sometimes I might not power it for weeks but when I need it I like for it to be running good. I have thought about a upgrade for it but as long as I can keep it running like it is it works fine for my needs. I will keep an eye open for the parts on the auctions.
Thanks again for your help.
Dave

[jholland1]

Dave
The NTE386 transistor is direct fit for the BP Boss machines. If you are in Arizona you are lucky. Boss machines do not like cold shops and will blow transistors like crazy when cold. Most of the time only one transistor out of 4 in a drive block will be bad. These transistors are NPN type and are all the same. To test use a multimeter and check resistance on ohm setting. The two catwhisker wires entering the case are leads. The base is on left, emitter on right. They are off center in the case to prevent accidental mounting the wrong way. A good transistor will conduct only in one direction. Typically you will have resistance of .400 to .800 ohms in one direction. When you switch probes you will have message from multimeter of open line. This should be a good transistor. A failed transistor will show resistance of less than .100 ohms and will usually conduct in both directions when probes are reversed.
I think you are correct about keeping machine as factory rather than converting to updated drive system. If you ran it daily update would make more sense.
jh

[machintek]

T2 is the large transformer in the top of the back cabinet. From the left, the 3 rd and the 6th red wire should be the Z axis. That should not exceed 63 VAC or you will blow a lot of transistors. Also the current measured at fuse 14 should be 8 amps.
Do you have a manual?

George

[cnc Rookie]

Pulled the Z transistor pad today and did a fine solder job on a new replacement.
I was able to find some local here in Phoenix....only $7 a piece. I didn't think that was too bad.
Many thanks for the help and guidance in getting me back up and running.
George...I do have a manual for BPT series I somewhere but have not been able to locate it. I believe it has been place where I wouldn't loose it when I moved into the new shop.
Thanks again...
Dave