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1980 FP3 with DC Drive Issues

jreiland

Aluminum
Joined
Mar 18, 2020
Location
Phoenix
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
 
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
 
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,
That’s a good idea, I haven’t tried that. Could I bypass the system and take the power that’s coming from the transformer to try this?
 
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.
 
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
 
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
 
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.
 
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
 
I had a chance to mess with this drive more and made some discoveries and have more questions.
The A2B board has all the correct resistors. I’m confident it’s back to stock configuration. The feed speed potentiometer still only works at full speed, 20 on the dial, if I turn it slightly less than that the drive almost stalls. If I turn it past center, the drive runs in reverse. It’s not a stock Deckel part, but is the correct spec per the wiring diagram. Thoughts?
 
The feed speed potentiometer still only works at full speed, 20 on the dial, if I turn it slightly less than that the drive almost stalls. If I turn it past center, the drive runs in reverse. It’s not a stock Deckel part, but is the correct spec per the wiring diagram. Thoughts?

Perhaps someone mistakenly replaced a linear potentionmeter with a log potentionmeter?
 
Reversing means the polarity of the speedsignal on terminals 5-6-7 has changed
AFAIK it is set with external potmeters
Check the voltage and polarity on terminals 5-6-7
Also check if there is a short in that cable somewhere
I had it once close at the terminal where they soldered a wire on the shielding That got hot and melted the isolation to almost nothing Over time it resulted in a short
I always put a pot directly on 5-6-7 and see how it runs then It should go from full forward to full backwards
That way you determen if its the board or something else

Peter
 
Reversing means the polarity of the speedsignal on terminals 5-6-7 has changed
AFAIK it is set with external potmeters
Check the voltage and polarity on terminals 5-6-7
Also check if there is a short in that cable somewhere
I had it once close at the terminal where they soldered a wire on the shielding That got hot and melted the isolation to almost nothing Over time it resulted in a short
I always put a pot directly on 5-6-7 and see how it runs then It should go from full forward to full backwards
That way you determen if its the board or something else

Peter

Peter,
Are you referring to terminals 5-6-7 on the A2B board?
 
I would have measured 4to5 and 5 to 6 and see for polarity
But better yet just disconnect the wires on 4/5/6 and connect a potmeter to it

Now it should run from max speed forward at 0% of the potmeter to zero speed at 50 % of the potmeter and then to max speed backwards at 100% of the potmeter
If is does that the drive is oke IMHO and the fault is somewhere else

On notice Some potmeters ,on the A2B probably, make it that the speedselector potmeter reacts only one direction



Peter
 
I would have measured 4to5 and 5 to 6 and see for polarity
But better yet just disconnect the wires on 4/5/6 and connect a potmeter to it

Now it should run from max speed forward at 0% of the potmeter to zero speed at 50 % of the potmeter and then to max speed backwards at 100% of the potmeter
If is does that the drive is oke IMHO and the fault is somewhere else

On notice Some potmeters ,on the A2B probably, make it that the speedselector potmeter reacts only one direction



Peter

Peter,
Just to clarify, I should hook the pot to the board or to the removed 4,5,6 wires?
 








 
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