Really fed up with my Bridgeport

I have a Bridegport Boss 5 Milling Machine. I installed a conversion kit from Slow Motion Controlls that transplants the CPU from the old 8
bit processor to a PC. It ran great for several years with the ocasional use on my home shop.
Lately, every time I used it it blows out the SCR driver transistors on the Y axis. So every time I went to use it I had to repair it first, sometimes twice and hopefully get thru the job. Then, the next time I would have to repeat the process.
An Expert had me pull the cards and had them checked by a repair shop. They came back OK and I waited several months before I had to use it again. They had me check the motor wiring and stepper coil resistances and for shorts to ground. All OK. Yesterday I hade a real need for the machine and put the cards in and fired things up. Everything ran, for a minute, then the Y axis driver failed. Then the Z axis driver did the same thing. Blew the Z axis fuse too.
I called a Bridgeport repair guy that was supposed to come to repair. He never showed. Went round and round for about 6 months with him but he has yet to show up.
I have really had it.
Anyone care to take a stab at this? It is a shame because I have a good amount of tooling and it does what I want it to do. Hate to see it hauled off to scrap. The machine is mechanically perfect. It came out of a Union R&D shop and never cut anything harder than plastic. It had seldom use. Ways are chrome and perfect. Ball screws are like new.
I am not a CNC Expert. With ocasional use I have to relearn what I forgot and hack my self thru a program.
What could I replace it with? Fix, scrap, trade????
Thanks, Bob in Central Illinois
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snipped-for-privacy@consolidated.net wrote:

The original Bridgeport stepper drive was crap - inventive for the time, but in light of today's drives, abominable crap! You should dump the whole works, electronically. If you want to stay with the steppers, go with Gecko drives and a PC. You have the choice of ArtSoft's Mach3 or the open source EMC.
If you want to upgrade the motors to servos, you have a number of choices. But, it is a waste to try to keep 30-year old motor drives running.

Yes, this is quite common. You can't GET iron like that anymore. Check out what even a manual Bridgeport costs today. Be seated when you check the numbers!
Jon
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Jon Elson wrote:

What he said.
Try visiting these forums:
http://www.cnczone.com http://www.machsupport.com
If you decide you want to just sell the thing cheap, let me know as I'd be interested in buying it and doing the conversion myself :)
Pete C.
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wrote:

Jon knows!
If you go to CNCzone, you will find an enormous wealth of information.
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On 25 Dec 2006 11:03:35 -0800, snipped-for-privacy@consolidated.net wrote:

Others can guide/have guided re suitable off-the-shelf replacement elex e.g. Gecko. If you have the time and inclination, it may be possible to save a few bux by modifying your elex to use more modern MOSFET drivers. Lemme know by email if you want to have a go at that, assuming that you have a schematic of your elex and some info on the stepper motors. They probably used SCR's as most suitable power semiconductors at the time, which would have been a loooooong time ago. I have a bit of trouble imagining driving steppers with SCR's.
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    [ ... ]

    Worse -- they used standard bipolar transistors -- in large banks, and at close to their maximum voltage.
    If he doesn't have the schematics, I do, and can send you photocopies.
    Enjoy,         DoN.
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On 26 Dec 2006 07:21:44 GMT, snipped-for-privacy@d-and-d.com (DoN. Nichols) wrote:

Great, DoN! Hold the schems for now, pending how Mr. Leonard decides to proceed.
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    [ ... ]

    [ ... ]

    If so -- send me an e-mail. My news has been rather messed up recently, and I had to jump through hoops to read this message. My e-mail in the headers and .sig is valid.
    Enjoy,         DoN.
--
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Kinda sounds like its trying to drive it both ways at once... I had this problem with a machine the used relays to drive the motor...
It was a weak relay spring that would not let it return fast enough...
snipped-for-privacy@consolidated.net wrote:

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Bob
I don't know where you are in central Illinois but you should make contact with Cardinal Engineering at Galesburg, IL.
Roland Friestadt (sp) runs the place and does conversions of old Bridgeport iron to Mach3 software and Gecko stepper drives.
He writes the articles in Home Shop Machinist about this type of upgrades.
Hugh doing a J head conversion to CNC using Mach3 and Geckos.
Email me direct for more help if you wish. I am in Quincy.
snipped-for-privacy@consolidated.net wrote:

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    Actually -- it did *not* use an 8-bit processor. It used one of the earliest 16-bit processors -- the DEC LSI-11. It had the same instruction set as the PDP-11 minicomputer, but drew a lot less power. This was with the BOSS-3 through at least the BOSS-5, and I think to the BOSS-8.

    Well ... you would not have these there to fail if you replaced the stepper motors with servo motors and the appropriate drivers (servo amps) -- but it *would* require a change in the hardware in the PC which is driving it.

    I don't see anything about checking the voltage -- either that applied to the system, or that applied to the drives. That system had a dual-voltage setup -- controlled by a separate magnetic amplifier (saturable reactor) in series with the power for each axis. When stationary, or at very slow step speeds, it would run at reduced voltage (IIRC, about 50V), and when fast stepping was needed, it would switch to 80V. This happened to be very close to the maximum voltage of the transistors available at the time. So -- if your line voltage is a bit high, you will pop transistors fairly often. If you have a rotary converter which has not been tuned, one leg will be higher in voltage than the other two, and will usually preferentially pop two of the three axes. If so -- *tune* it. If it is real three phase from the power company, get it turned down.
    So -- get a voltmeter and first check the three 240V phases coming into the machine. Then check the voltages fed to the axis driver transistors. (Do you have the manual which has all the drawings to show you where to probe?)
    And the transformers on the system have lots of different jumpers to adjust it to either 240V or 460V or 208V or some others. It might be possible that it is jumpered for 208V and you are feeding it 240V. What were you driving it from in your home shop? Are you still in your home shop? (With a Bridgeport repair guy on call (sorta) it sounds like you are in a shop with incoming three phase power. Maybe the line has been tweaked because someone else in the neighborhood needs a bit more voltage. You may need the power company to feed you from a different set of taps.

    Well ... I've just told you what is most likely to be causing the stepper motor drivers to pop. If you were closer, I could give you two spare doors with extra sets of transistors installed. I'm (slowly) changing over to servo motors -- for other reasons than the power transistors popping.

    You have some suggestions above. My own preference is to replace the stepper motors with servo motors -- but the Y-axis one is a problem to fit, because servo motors are usually a lot longer than the steppers. No problem for Z-axis and X-axis, but the Y-axis points in towards the knee. (There are alternative mounts for the Y-axis motor which angle down to the right, so the motor sticks back beside the knee instead of into a cavity in it just the right size for the stepper motors.)
    I hope that this helps,         DoN.
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Thanks for your suggestions. I traced things down to the ACC Card allowing current too high to the Y axis motor. I have a new one en route. Will keep fingers crossed.
Thanks guys,
Bob
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