Repair of an old JJ LlOYD T20K tensile machine

[Tiqo]

Hello,
I am currently a mechatronics engineering student, I am working on a school project: retrofitting a tensile machine.

The goal of the project is to improve the human-machine interface as it is a very old machine, it is a JJ LOYD T20K, my problem is that the machine no longer works(it works sometimes... very rarely!), when I command it up or down nothing is happening.

I tried to see if there is indeed a voltage at the terminals of the two motors ( SHUNT DC MOTOR), the voltage is zero at the terminals of the armature, but it is 230v at the terminals of the shunt field.
(The voltage across the armature is different from that of the inductor ( for speed control...) and same for maximum speed)

As I don't have the documentation of the machine (I already contacted the manufacturer they told me they couldn't do anything for me...), I tried to find the cause of the problem, but I can't manage it !
I would like to know if one of you has already used this machine, if he has had the same problem, if he has his documentation...

What could be the cause of this malfunction?!
Thank you.

 

[trurle]

Hello,
I am currently a mechatronics engineering student, I am working on a school project: retrofitting a tensile machine.

The goal of the project is to improve the human-machine interface as it is a very old machine, it is a JJ LOYD T20K, my problem is that the machine no longer works(it works sometimes... very rarely!), when I command it up or down nothing is happening.

I tried to see if there is indeed a voltage at the terminals of the two motors ( SHUNT DC MOTOR), the voltage is zero at the terminals of the armature, but it is 230v at the terminals of the shunt field.
(The voltage across the armature is different from that of the inductor ( for speed control...) and same for maximum speed)

As I don't have the documentation of the machine (I already contacted the manufacturer they told me they couldn't do anything for me...), I tried to find the cause of the problem, but I can't manage it !
I would like to know if one of you has already used this machine, if he has had the same problem, if he has his documentation...

What could be the cause of this malfunction?!
Thank you.

You should check first the resistance between armature (rotor) and power source, and secondly input resistance at power input terminal . From description, you seems to have a loose ohmic contact somewhere in the armature circuit, or may be worn out over-voltage protection module at armature power input.

 

[Tom.G]

That does seem to be a rare beast, it has been replaced with Model LRX. I did find an equipment rental business that at least shows it on their website. They are in San Diego, California, USA but claim to ship worldwide. They may have some documents, or ideas on where to find more info, especially if you beg them as a student.
https://www.atecorp.com/products/lloyd/t5100
If that fails, perhaps you can get someone from your Electrical/Electronic dept. to help.

Good Luck, and please keep us updated,
Tom

 

[Tiqo]

You should check first the resistance between armature (rotor) and power source, and secondly input resistance at power input terminal . From description, you seems to have a loose ohmic contact somewhere in the armature circuit, or may be worn out over-voltage protection module at armature power input.

Hello,
Thank you for answering me so quickly.
This board is between the power source and the two motors.
Can you identify where is the over-voltage protection? otherwise what is his role?
PS: when I press start the two resistors R23 and R24 heat up a lot, I desoldered to measure their resistance, it is the same as indicated on them 100 ohms.

 

[trurle]

I can not clearly identify over-voltage protection (varistor or zener diode) on this PCB.
Following items need to be checked first:
1) Fuse? RR1
2) D11, D13
3) Electrolytic capacitors - three large black cylinders (these are very likely to fail due old age)

 

[Asymptotic]

Can't make them out clearly, but transistor date codes seem to be '2179', so heed @trurle's observation about electrolytic capacitors. 40 years is a long time in cap years. C2 looks like a tantalum capacitor, and (although tantalums are more stable than regular electrolytics) can also go bad as they age depending of how they were manufactured. Those using magnesium dioxide electrolytes tend to live longer than the polymer ones. They can be pulled and tested, but small electrolytic caps are cheap, and on older equipment it's common practice to simply replace them as a troubleshooting step.

I've run into trimpots similar to those on this board that (presumably) formed an poorly conductive oxide layer between wiper and resistive substrate, and were 'fixed' by simply exercising them a couple of times. A short squirt of contact cleaner while exercising helps. Before proceeding, it's a good idea to mark wiper position (marking the PCB with a sharpie, for example), and measure/record resistance between wiper and one of the 'end' terminals so they can be returned to 'as-is' states. Measured resistance ought to closely match recorded resistance after returning the wiper to the original position. If it doesn't, it's a clue you've found an actual problem.

Brushed DC motors?
Check brush length and condition, and motor commutator surface patina.
Check shunt field resistance.

230V is across the shunt field terminals. So long as shunt current is actually flowing and creating a magnetic field the motor shaft ought to revolve with application of armature voltage (provided the shaft isn't mechanically overloaded). For troubleshooting, one course of action is to disconnect motor shaft from the mechanical system, isolate armature wires from the DC drive controller board, and connect them to a variable DC supply capable of delivering adequate current. If the shaft turns, no arcing is observed between brushes and commutator, and speed follows applied armature voltage, chances are the motors aren't the problem.

All live electrical testing is inherently dangerous. Take proper precautions. Enlist the aid of an electrical/electronic tech.

 

[Tom.G]

@trurle spotted the most likely suspects as the electrolytic capacitors. The date code on SCR2 and SCR3 show 2179, the 21st week of 1979, making the board 40 years old. Consider that to be two to four times the life expectancy of electrolytics. First replace them and see if the board works, there is a fair chance that will fix the problem. Replace all 6 of them, the three black ones (C11, C3, and its neighbor) and C2, C4, C5. Based on their packaging, C2,4,5 may be Tantalum electrolytics rather than Aluminium, be sure to get the correct replacements.

If there is no change, the next steps would need an electrical block diagram of the machine (the more detailed the better) and probably a schematic of the circuit board(s). Given a good block diagram, we may be able to help you find the problem(s) with step-by-step troubleshooting guidance.

Once traced down to board level, a schematic of the board with parts values is just about mandatory; which means somebody will have to create that schematic from the board itself. Doing so remotely without the hardware in hand is possible with good photos and single- or double- sided boards, but it is both... challenging and time consuming. That's why I suggested help from your Electrical/Electronic dept. if possible.

Oh, I see @Asymptotic responded at the same time with some of the same observations.

Cheers,
Tom

p.s. It appears from your description and the component markings on the board that it controls the motors with pulse-width modulation, probably by phase control of the AC power line to control the effective DC voltage.

 

[Asymptotic]

Oh, I see @Asymptotic responded at the same time with some of the same observations.

Except for my "seeing" transistors that are actually SCRs. ;)
I'm used to SCRs in TO-220 packages, or "hockey pucks" of various sizes, but not metal cans (are those TO-66?).

 

[Tom.G]

(are those TO-66?)

Sure look like it, too small/wrong aspect ratio for TO-3.

 

[Tiqo]

@Asymptotic
I have already tested the two motors by connecting them to a variable DC supply and without disconnecting them from the mechanical system, both motors work perfectly !

 

[Asymptotic]

@Asymptotic
I have already tested the two motors by connecting them to a variable DC supply and without disconnecting them from the mechanical system, both motors work perfectly !

Excellent!

my problem is that the machine no longer works(it works sometimes... very rarely!),

If there aren't problems with the motor and load (and provided good wiring connections to the motor) then it is probably the drive controller that works only sporadically. Re-cap the PCB as outlined in post #7. Doing this alone may bring it back into normal operation.