Hi all,

I put in the replacement transistors to replace all of the X-axis transistors as a set. After replacing all 4, I was able to jog (or step, can't remember) the X axis! 10 seconds later I tried it again and the axis wouldn't move. So that's what frustration is...

Any help on what's happening here so that I don't keep replacing transistors? The same transistor failed both times. It's the bottom one on the X panel (is that Q4?) I can order a more robust transistor, but that seems to be fixing the symptom and not the disease.

I have the readings for T2 output voltage checks that I did at home, and I think that one or two of the numbers were a little high. I will post the numbers from the different terminals a little later today to see if that helps. What exactly causes the transistor to pop, and how can I track it down? Is it over current or over voltage, or reverse voltage or current spikes? I've got the schematics, but don't know what the common culprits are.

Would now be a good time to remove FU12, stick an ammeter inline there, and adjust the current at P1 of the SMD board to 8.2 amps? I'm a little hesitant to do that, but I may have to. Please let me know what you think. Thanks!!

Ian

I meant to say: Would now be a good time to remove FU12, stick an ammeter inline there, and adjust the current at P1 of the ZCK board to 8.2 amps?

By the way, this is a Series I Boss 6 with an SMS board. TIA,

Ian

The other night I performed the electrical checks listed in the maint. manual to diagnose the first time that the transistor blew. On the output of the T2 transformer (terminals 5 and 6), here's what I got:

5A-6A= 58V
5A-6B= 57V
5A-6C= 53V
5B-6A= 53V
5B-6B= 58V
5B-6C= 55V
5C-6A= 68V
5C-6B= 66V
5C-6C= 70V

According to the manual, these numbers should be between 57 and 63V. The numbering convention is due to the fact that each number has 3 terminals to measure from (A,B,C as viewed from left to right).

As you can see, values from the 5C terminal to all of the #6 terminals (listed in red) are outside of the allowable range. Does that point to dirty power from the wall (actually a rotary phase converter), a bad transformer or what?

I'd like to put this thing to bed, so any input, even if it's only part of the solution would be very helpful. Thanks to all!!

Ian

You also may have a motor with an intermittent short in the windings. That will take transistors out.

Mariss

That's a good possibility Mariss. How do I rule that out?
Ian

The motor current is adjusted at the ACC board. You can adjust the current down for trouble shooting.

There are always 2 final transistors on at a time. I had a SMD board with a bad predriver that would make one final transistor try to carry the full 8 amps, blowing it everytime. By reducing the current I was able to trouble shoot it under power without blowing the final.

Darek

The 1st and 4th wire are X axis, The 2nd to 5th is the Y and the 3rd to 6th is the Z. look at it that way. 58 VAC is great!

George

I swapped fuses F12 with F13. Then I pulled the F12 fuse and put an ammeter across it and got 8.7 amps. I dialed that down with P1 on the ACC board to 8.1 amps. In the meantime, I blew the top transistor on the X board. Once I replaced that, the X axis will step, and hasn't blown the transistor yet! I'm still not sure if I'm entering the step mode correctly though...

Going onward from here, I'd like to do the following:
-Replace the screw in type fuses F12, F13, F14 etc with snap in type holders. Anyone have a good part number for those? I typically shop at Mouser.
-Order replacement fuses for the above holders. Again, any specs or part number available on those?
-Order some more transistors with a higher rating to keep on hand.
-Turn down the rapid speed on the ZCK board using Pot 3, as a preventative measure.
-Install Hillbilly's BOB which just arrived as I was typing this post!!
I am thinking that the BOB will not affect the problems that I've been having with the ACC board, since the BOB is more of a brain transplant and not a muscle transplant, if that metaphor makes sense.

If there are any other good steps to take as preventive measures I'm all ears.

Should I be concerned about the 70 VAC on the Z axis? No problems with that axis yet.
Thanks to everyone for their continued ideas!
Ian

Well, the X axis transistor keeps popping. I'll do all the things that I stated in my last post, but I need to take a break and think things through.

At this point I'm trying to decide what's the best thing to swap with the Y axis. motor, SMD board... Any more suggestions?

BTW Hillbilly, is your BOB likely to help me rule out any likely culprits on the control side of things if I install it before the X axis is fixed? Would it hurt anything to install it with this problem still in the mix?

Thanks to all for any input.

Ian

By replacing transistors, you may be curing symptoms as opposed to cause.

How much current is REALLY being asked for by the device that is connected to the failing transistor?

Is there binding that is causing high current draw? What about motor? Short, siezed bearing, hang up in drive mechanism, whatever?

Could there be a short on the SMS board? Or the downstream wiring?

Just more ideas to look for/at. Sometimes it takes a keen eye for the obvious to figure out what's REALLY wrong.

At this point, it seems to me that the most likely culprit is the X-axis motor, bridge rectifier 3, or the 'wild leg' of the rotary phase converter. I swapped the X and Z SMD boards, and there were no problems on the Z axis, so that seems to rule out the X SMD board. Also, I plan to flip the ACC board, which should swap the X and Z inputs to rule out the ACC board too. On a side note, when I removed the rubber seal on the X axis motor (around the cable) a tablespoon or so of oil came out. I didn't read any shorts across the wires though. I'll keep pluggin' away!

In my machine, I use the 2 "normal" legs for powering the transformer that runs everything except the 3 ph motor. In my case, I just turn on the disconect on the back of the machine without starting my 3 phaser. You will find that all the controls and table movement work fine and that you really only need the third leg to run the spindle. This wliminates problems related to the wild leg voltage / current.

I checked the BR3, no problems. I've ruled out the phase converter since I was able to measure clean power at the output of T2 for the X axis. That seems to leave only the motor.

I need to track down a Megger and check the windings of the X motor, as well as all associated wiring for that axis. Looking at the bottom right of the door to the side cabinet, I can see where the wires head out to the different motors. Does anyone know of a reason that I couldn't swap the leads to the X and Y axis motors there and see if the replaced transistors on the X axis will drive the Y motor without any problems, and conversely, if the X axis motor causes any problems with the Y final drive transistors?

Can anyone list in one place the actual physical locations of the components (diodes and resistors) that make up just the X axis return circuit? Essentially, I'm looking for everything between the X motor and ground. Thanks!!
Ian

I just spoke to a customer that has not blown a transistor in years. There is a reason if one blows.
As I said before, The output of T2 is critical. From my experience, 63 VAC and greater increses the chance by a LOT. T2 is a three phase transformer. Intermittant connections (and bad fuses) will blow a transistor. Not the transistor turning on but it is turning OFF when they blow. Current set at 8 amps. The correct transistors used. SMS board used. Spike suppression diodes used. Good insulators and heat transfer paste.ETC.
Components are all over the place. Large resistors on the door that also has the transistor blocks. Another board with diodes is below the ACC board. The Bridges are behind the large capacitors. I usually take out the tape reader when getting to them. AC fuses in the back cabinet with T2. DC fuses above the logic boards.
I have had people drop screws, washers and chips between the wires on the terminal strip on the bottom of the door creating a short that acted like a shorted transistor. I have had people forget the insulators beneath the transistors or the insulator beneath a screw and call me. I had one person in TN lose a terminal strip screw and put in a longer one, just long enough to grab the terninal and short to the chassis beneath it. That took a while. Wait till you have one of those 12 diodes short on the board beneath the ACC. That is a fun thing to find! Makes changing the bridge easy. I have also had the 5 VDC zener go into intermittant conduction in the logic power supply. Another beauty.

George

I've noticed something important. After the latest transistor swap, I fired up my home-made rotary phase converter (3 HP motor, capacitor start). Once it was running, I plugged in the mill. Then I threw the main contactor switch on the BP. I was still in Jog mode from the last time, so I started by checking the jogs of the Y and Z axes. Then, holding my breath , I tried jogging the X axis. NO PROBLEM! I wasn't shy either, back and forth several times without a hiccup.

Next, I try to turn on the spindle...NO GO. That was the first thing that I posted, it happened the first time that I fired up the mill. That first time the X axis was working fine.

I threw the main contactor to OFF, and kill the phase converter. I wait a few seconds, and turn the phase converter back on again, never having removed the power cable. I threw the BP contactor to ON, and tried the spindle. It starts right up, and works in CW and CCW directions. I try the X axis again, and it's toasted. The Y and Z still work fine.

I checked the outputs of the T2 transformer, before I turned anything off, and the 3rd and 6th terminals from the left measure 70 volts AC, and the 1st and 4th terminals measure in the mid 40's, as does the 2nd and 5th uif I remember correctly.

This leads me to believe that something involving the phase converter is causing this problem. The first time, I think that I must not have been receiving 3 phase power since the spindle wouldn't turn on. Correct me if I'm wrong, but the spindle is the only thing that requires 3 phase power.

There may also be something wrong with the way that I start up and power down the mill and/or the phaseconverter. Does any of this sound plausible??

Ian

T2 requires 3 phase power and the spindle motor requires 3 phase power.

George

Turning the spindle on may cause the transistor to blow. It seems that I can run the X axis back and forth after replacing the transistor, but that after turning the spindle the transistor is blown again. Is there any way that the spindle could be spiking the current to the X drive, or drawing down the current from the 3HP rotary phase converter that I have and blowing the X axis final drive transistor?

Here's what I've also done to try and rule out as much as I can:
I flipped the ACC board to put a different portion of it's circuit in control of the X axis
I swapped the SMD-X for the SMD-Z board.
I isolated and checked the top 4 stud diodes on the right side of the door that are in the X axis system.
I checked all the X axis diodes on the little board next to the terminal strip in the bottom right of the door (not the SMS board)
I swapped the cables for the X and Y motors, but I left the X5 and Y5 lines from FU12 and FU13 in their correct places.

After doing all of the above mentioned, I was using the Y setting on the control panel to jog the X axis motor, and it worked fine (that would seem to rule out any problems with the X motor and associated cabling from the terminal strip out to the motor). Then I turned on the spindle, let it run for a few seconds, and turned it off. I tried moving the X motor with the Y controls, and it worked fine. Next I tried to move the Y motor with the X controls (remember that I swapped the motors and cables above) but the Y motor would not move.

This leads me to believe that the SMD and the ACC boards aren't the culprit since they both have been swapped or flipped. Also, it seems that the cabling and motors are fine. What does that leave? The spike suppression circuitry? SMS board or small diode board at the bottom of the door that is between the terminal strip there and the resistors above? A possible connection to the spindle circuitry and any spikes that it may cause? I think I've checked everything, but maybe I've missed something. Also, please see my post about -12V unregulated voltage being low if that could affect this.

Thanks to all for your continued very knowledgeable help!!
Ian

Finally figured it out!!

The last owner of the mill had added buck and boost transformers to the input line. They put the voltage for one of the axes out of limits, and that seemed to cause problems on the X axis.

Also, probably just as important, I finished building my RPC out of a 10 HP Ronk Rotocon Mark II motor. I think that the power is now much more balanced than what I was getting from my old 3 HP RPC. Between the two 'fixes' the mill has been behaving very well-no blown transistors yet. Life is great!! Now on to the Hillbilly breakout board installation. Thanks to everyone for the excellent advice!!

Ian

One thing that nobody looked at is that the Capacitors in the power supply for the drives have a max life , they don't last for ever, I would think as caps
go the voltages start to trop and the amps go up and the transitors blow.
I went through the same thing, and ended up ripping all that old stuff out, you be glad you did once it runs on new drives.

Frank