1980 FP3 with DC Drive Issues
Close
Login to Your Account
Results 1 to 9 of 9
  1. #1
    Join Date
    Mar 2020
    Country
    UNITED STATES
    State/Province
    California
    Posts
    18
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    0

    Default 1980 FP3 with DC Drive Issues

    Hi All,

    I recently received this machine from a fellow PM member with known DC drive issues. Machine arrived better than he described and I’m trilled to have it.

    I’m picking up where he left off with trying to get the feeds to work properly. Ive traced all wires per the diagram and found them to be in the correct place. The issues is similar to the weak Z up post in where the DC drive motor seems to have very little power. Ive replaced the potentiometer with a 10k as suggested in previous posts, with no change in operation. DC motor runs only when potentiometer is all the way to one side, and is off when in slow speed setting. Still very weak in all directions, specially Z up which acts as if the motor is stalling. The rapid does speed up the drive, still weak z up. The creep in the other hand does not work. When pressing the creep button, the relay clicks but the drive motor turns off, the power up sequence must be done (blue and white together) to get it back running. I have new caps coming based on other posts, hoping that will fix the issue.


    I’d like to replace the A2B board with a known good unit, the one I have has several traces redone, although they look to be in good shape, it would be nice to have a unmolested part.

    If theres anyone in the NorCal area that has some knowledge of this machine I’d gladly pay you for your time to help diagnose, I’m in Oakland.

    Thanks in advance

    Jon

  2. #2
    Join Date
    Jul 2002
    Country
    UNITED STATES
    State/Province
    California
    Posts
    3,385
    Post Thanks / Like
    Likes (Given)
    20
    Likes (Received)
    68

    Default

    OK, this is kind of a brain dead question.... unless you haven't gone down this path!

    I'm assuming you have tested the voltage being delivered to the servo, right? If so, have you tried supplying power to the servo, directly, from a different source. Maybe the motor is having issues and not the circuit.

    Alternatively, you can often put a load on the output of circuit and see how well it is behaving. For repair of DC servo systems, it is not uncommon for people to use light bulbs. The intensity of the bulb is, of course, something that would correspond with the speed of the motor.

    Yeah, I know there isn't any rocket science in what I'm talking about, but I haven't seen the other thread about this topic. It is possible that you never looked at the whole problem from a different angle. As such, I figured I'd err on the side of being a bone head.

    Alan

  3. #3
    Join Date
    Mar 2020
    Country
    UNITED STATES
    State/Province
    California
    Posts
    18
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    0

    Default

    Quote Originally Posted by wrench View Post
    OK, this is kind of a brain dead question.... unless you haven't gone down this path!

    I'm assuming you have tested the voltage being delivered to the servo, right? If so, have you tried supplying power to the servo, directly, from a different source. Maybe the motor is having issues and not the circuit.

    Alternatively, you can often put a load on the output of circuit and see how well it is behaving. For repair of DC servo systems, it is not uncommon for people to use light bulbs. The intensity of the bulb is, of course, something that would correspond with the speed of the motor.

    Yeah, I know there isn't any rocket science in what I'm talking about, but I haven't seen the other thread about this topic. It is possible that you never looked at the whole problem from a different angle. As such, I figured I'd err on the side of being a bone head.

    Alan
    Alan,
    Thatís a good idea, I havenít tried that. Could I bypass the system and take the power thatís coming from the transformer to try this?

  4. #4
    Join Date
    Jul 2002
    Country
    UNITED STATES
    State/Province
    California
    Posts
    3,385
    Post Thanks / Like
    Likes (Given)
    20
    Likes (Received)
    68

    Default

    No... that won't work.... Transformers are implicitly AC devices. They work on changing magnetic fields, which induce a voltage in the other (secondary) wiring. Bit off topic here, but the primary and secondary coils are electrically isolated from one another. You could 'ring them out' all day long and you'd never have any continuity. They are inductively coupled only. This is all physics, if you are curious.

    Anyhow, the point is... A transformer will produce AC output, *NOT* DC. You get DC by putting the transformer output into a diode bank, typically a full wave bridge. The orientation of the diodes is such that you end up with a bunch of mountains, if you will, on a flat baseline. Think of it like a sine wave centered around zero volts, but instead of going negative, the wave goes back positive. Or think of it like a ball bouncing down a street... it never goes below the street level, it just bounces back up. This is what you'd see on a scope for a fully rectified output of a transformer. You "flatten" it to a constant DC by introducing capacitors. These charge up and then discharge as the voltage drops back to zero. It is a "push/pull" thing such that you start to flatten the output so that it is "constant" or DC.

    The point here isn't so much to give a lesson on electronics but to say that if you have a DC servo (which I'm almost certain you do), then you do *not* want to feed it an AC voltage. At best, it will just buzz and probably scare the (well, you get the idea) out of you! :-)

    It is hard to say what power you really put into that motor, but I'm guessing it isn't all that great. If you had a decent sized DC power supply you could try that. A good one will have an overcurrent protection so you wouldn't hurt the supply. You could also buy a ready made DC motor controller from any number of source. Depending upon the voltage, you could even use a battery. However, before you pull out your car battery and try this, there are a few words of caution. First, car batteries have a ton of energy in them and simply hooking a wire up to them provides no fusible link except the wire... it is not the best of ideas! Second, car batteries generate explosive hydrogen gas. This is why there is a prescribed way to hook up jumper wires. You don't want to ignite that gas or you'll end up with sulfuric acid blowing up all over the place. That could blind you or kill you.

    There are lots of sources for low voltage DC, which I strongly suspect (but cannot confirm) is what your servo is using. Do you have any specs for that motor?


    BTW, I'm in Sunnyvale and grew up in Bezerkely. Unfortunately, I am not really doing much traveling due to covid. I do need to perform a spindle grease rebuild with another member sometime though, during which time I might be able to provide some help. I'm pretty rigorous with my social distancing and protective protocols though.

    Feel free to add photos, scans of manuals, etc on this posting. Alternatively, you are welcome to contact me at 'deckel dot dvd at gmail etc, etc'. (I'm sure you can decipher all of that. . However, at some point I'd like to tie it all back into this post so that others may benefit from the information.

  5. #5
    Join Date
    Mar 2020
    Country
    UNITED STATES
    State/Province
    California
    Posts
    18
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    0

    Default

    Quote Originally Posted by wrench View Post
    No... that won't work.... Transformers are implicitly AC devices. They work on changing magnetic fields, which induce a voltage in the other (secondary) wiring. Bit off topic here, but the primary and secondary coils are electrically isolated from one another. You could 'ring them out' all day long and you'd never have any continuity. They are inductively coupled only. This is all physics, if you are curious.

    Anyhow, the point is... A transformer will produce AC output, *NOT* DC. You get DC by putting the transformer output into a diode bank, typically a full wave bridge. The orientation of the diodes is such that you end up with a bunch of mountains, if you will, on a flat baseline. Think of it like a sine wave centered around zero volts, but instead of going negative, the wave goes back positive. Or think of it like a ball bouncing down a street... it never goes below the street level, it just bounces back up. This is what you'd see on a scope for a fully rectified output of a transformer. You "flatten" it to a constant DC by introducing capacitors. These charge up and then discharge as the voltage drops back to zero. It is a "push/pull" thing such that you start to flatten the output so that it is "constant" or DC.

    The point here isn't so much to give a lesson on electronics but to say that if you have a DC servo (which I'm almost certain you do), then you do *not* want to feed it an AC voltage. At best, it will just buzz and probably scare the (well, you get the idea) out of you! :-)

    It is hard to say what power you really put into that motor, but I'm guessing it isn't all that great. If you had a decent sized DC power supply you could try that. A good one will have an overcurrent protection so you wouldn't hurt the supply. You could also buy a ready made DC motor controller from any number of source. Depending upon the voltage, you could even use a battery. However, before you pull out your car battery and try this, there are a few words of caution. First, car batteries have a ton of energy in them and simply hooking a wire up to them provides no fusible link except the wire... it is not the best of ideas! Second, car batteries generate explosive hydrogen gas. This is why there is a prescribed way to hook up jumper wires. You don't want to ignite that gas or you'll end up with sulfuric acid blowing up all over the place. That could blind you or kill you.

    There are lots of sources for low voltage DC, which I strongly suspect (but cannot confirm) is what your servo is using. Do you have any specs for that motor?


    BTW, I'm in Sunnyvale and grew up in Bezerkely. Unfortunately, I am not really doing much traveling due to covid. I do need to perform a spindle grease rebuild with another member sometime though, during which time I might be able to provide some help. I'm pretty rigorous with my social distancing and protective protocols though.

    Feel free to add photos, scans of manuals, etc on this posting. Alternatively, you are welcome to contact me at 'deckel dot dvd at gmail etc, etc'. (I'm sure you can decipher all of that. . However, at some point I'd like to tie it all back into this post so that others may benefit from the information.
    I did not try to connect the transformer directly to the motor, I got a text from a friend who’s on the forum warning me that it wouldn’t work - AC vs DC. Unfortunately I don't have spare components to swap out and try as part of trouble shooting, nor do I have a DC power supply with enough output to support the motor. The data plate is missing from the motor, it appears to be a stock.
    I'll shoot you an email off forum to coordinate a potential meetup, socially distanced of course.

    -Jon

  6. #6
    Join Date
    May 2013
    Location
    Germany, New Zealand.
    Posts
    93
    Post Thanks / Like
    Likes (Given)
    19
    Likes (Received)
    21

    Default

    Hi,

    Here is a picture of the stock motor on a FP2, I expect it is very similar or the same as yours. Hope it is if some help.59dfa770-9c1a-4617-ac8d-5d57a12ad67f.jpg

  7. #7
    Join Date
    Jan 2005
    Location
    The Netherlands
    Posts
    6,073
    Post Thanks / Like
    Likes (Given)
    295
    Likes (Received)
    1642

    Default

    Before making to much costs remember that a new drive is only about 600 euro from the OEM
    They can also repare the old one for about half that cost Prices are ex shippingcost from Germany
    To test the DC motor connect it to a battery pack from a forktruck or simular That is as DC as you can get it
    Cleaning out the black crud inside the motor might help too But keep the rotor inside the stator Never take the rotor out That might be a couse too Someone took out the rotor and the magnets went weak A good motor repairshop can fix that
    I have replaced several of these motors which were in bad condition
    New they are very pricy so I looked for used ones

    Peter

  8. Likes AlfaGTA liked this post
  9. #8
    Join Date
    Mar 2020
    Country
    UNITED STATES
    State/Province
    California
    Posts
    18
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    0

    Default

    Quote Originally Posted by Peter from Holland View Post
    Before making to much costs remember that a new drive is only about 600 euro from the OEM
    They can also repare the old one for about half that cost Prices are ex shippingcost from Germany
    To test the DC motor connect it to a battery pack from a forktruck or simular That is as DC as you can get it
    Cleaning out the black crud inside the motor might help too But keep the rotor inside the stator Never take the rotor out That might be a couse too Someone took out the rotor and the magnets went weak A good motor repairshop can fix that
    I have replaced several of these motors which were in bad condition
    New they are very pricy so I looked for used ones

    Peter
    Peter,
    Based on the photo from Boat Brat, the motor can handle What looks like 165 volts (hard to see). With the feed pot all the way up, I’m getting 80 volts on each of the legs going to the motor = 160 volts. At that voltage it should be at its fastest/strongest? Am I reading that right? If that’s the case, the motor could be my issue.

  10. #9
    Join Date
    Jan 2005
    Location
    The Netherlands
    Posts
    6,073
    Post Thanks / Like
    Likes (Given)
    295
    Likes (Received)
    1642

    Default

    At max speed the drive should generate 165 volts DC But when the motor is bad the drive cannot get to that 165 volts perhaps Perhaps you can measure the drive with the motor disconnected I think it should go to max speed/voltage at any setting of the ptmeter as there is no input from the tacho
    Get a clamp ampmeter Check how much the AC side is pulling
    But I would start with cleaning the motor out
    That carbon dust is conductive
    Perhaps it is wise to have the motor inspected at a motor repair shop
    Peter


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •