As a printing and publishing company, including a bindery, our strapping machines get used a lot!
Consequently, they need frequent periodic repairs.
This page is dedicated to one of the type of strappers we use, the Signode model MST.
Since I am so accustomed to reading ladder diagrams for machine wiring, I found it necessary to transcribe the factory supplied drawing into something legible.
The drawing I reconstructed, is currently in two parts. Perhaps someday whan I have time enough (dream on), I may consolidate them onto one page.
Until then, these are for helping out anyone else who could use an easier to read schematic.
I also found myself needing a more accurate portrayal of the event sequence of these strappers than what the manufacturer's manual provides, so I documented this sequence chart that should be a benefit to anyone working on these machines.
I assume no liability for any problems that may result from the useage of this information, as there may be errors, or different factory versions.
Adobe Reader is necessary to view the following PDF files, and can be downloaded from this website:
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| Factory wiring PDF | Ladder Page 1 PDF | Ladder Page 2 PDF | |
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| Sequence Chart PDF | PC-18B PDF |
Recently, on one of our strappers, the "Motor Auto-Stop" pc board # PC-18B, caught fire, and I found it well toasted. I don't know exactly what caused it, but I suspect it was the victim of the infamous "Pepsi Syndrome". Actually, a layer of the sticky evidence of what appears to have been Mountain Dew, was coincidently found puddled across the top of the machine. Anyway, I was shocked to find out the miniature pc board quoted at $330.00, plus tax, and shipping etc.. I detest paying such an unreasonable price for such a simple unit. I can't imagine the pc board exporting out of Japan for more than $50.00, and so I determined to attempt a smart relay, or plc replacement. I was able to decipher the circuitry, as well as the other two pc boards, which are also outrageously priced. If I have and make time, I will display their documentation also. I have succeeded in using a Crouzet CD12 24VDC unit to replace the burned up pc board, and have figured I can also replace the PC-22B pc board with it as well, if I get time, and, or if it goes bad too. The PC-18B, is merely as it's title describes it, a motor automatic stop unit, which allows the motor to continue to run for a minute, after any of the three inputs, wire #s, 6, 10, and 20, trigger the motor to start. I chose to remove the transformer T-1, and it's associated bridge rectifier, and 470 micro-farad capacitor, and replace them with a decent power supply, since I was reading voltages as high as 40 volts from it. You can obtain a fair priced power supply, from Circuit Specialists. The bridge rectifier, and capacitor, were removed from the relay pc board. Furthermore, I had to reverse the overall DC polarity (wire #2 becomes positive, and wire # 1 becomes negative), since the existing circuitry is sinking, and the plc needs to be sourced. The relays are not polarity specific, although the remaining electrolytic capacitors on the relay board need to be swiveled, in regards to polarity. The solenoid has it's own bridge rectifier, which is isolated from the affected changes, so nothing needs to change concerning it. The two wire numbers, 7, and 8, need to be swapped, which connect to PC-22B. With the wiring connector disconnected from it's pc board mate, those two wire pin terminals can be easily removed from the connector, by pressing into the exposed metal on the side of the connector (with a small screwdriver), while pressing the terminal toward the wire as well, and then reinserted once the wires are swapped. I did the same thing with the clutch wires, # 11, and 12, also, not knowing if the clutch coil is polarity specific, or not, and not wanting to take a chance. I also inserted a 1N4007 diode in series with each of the three inputs to the plc, paying attention to correct polarity. Last of all, the program is simply, all three inputs in parallel to a timer in the plc, and the timer contact to an output, which will switch an external relay, to switch the motor (wire #s, 15, and 18). I suggest using also an arc suppressor.
PC-22B, is simply an adjustable timer, to actuate the solenoid. Terminals 1, and 2, lead to a contact which closes to energize the solenoid, using a relay on the small pc board.