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Problem replacing a faulty C20 with a used C20

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Hello everybody, I bought a second hand Sysmac C20 to replace a faulty one in a dyeing machine. I took out the memory chip from the c20 I bought and I replaced it with the one that contains the required program. When the machine was started the didn't give any error/fault signal. However, it appears that the PLC is not running the required program. Can anyone tell me what could be the problem? Do you think the PLC is faulty?

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Did you set the dip switches. Check the old unit and set the dip switches in the "new" unit the same. Make sure the unit is not powered up when changing the switches and / or installing the chip. Hope this helps.

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Thank you qtsuport. Yes the dip switches were exactly same. I thought maybe the PLC is still running the old program because of the battery. The problem is that the omron manual does not state whether the cpu reloads the program from the memory at every startup.

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Can you tell me the on/off state of the dip switches?

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Thanks qtsuport, The DIP switch setting if I remember well is: ON-OFF-ON-OFF I always thought it to be an eprom. However, I can confirm that tomorrow and I will also give the memory chip description. Do you think the chip can go faulty and the cpu isn't aware?

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Based on the switch settings you are remembering, you are set up for RAM not EPROM. The RAM chip number would be RAM-G (depending on the CPU number). The EPROM chip number would be ROM-H. Check the number on the chip. This may be the problem. It appears, depending on the CPU that you have, this may be similar to the C--K processors. Depending on how the switches are set, you could have two different programs in the unit, one in RAM, and one in ROM. By changing the switches, you could change between the two programs. Good Luck!

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Thanks again, You are greatly helpful. Anyways, I will confirm the DIP settings tomorrow and also the chip number. The cpu is 3g2c7-cpu74e.

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Based on the CPU number, I really think the dip switches are the problem. The CPU that you have, based on the manual I have, shows that NO chip is required for RAM operation. And the dip switch settings for RAM operation are 1=On, 2=Off, 3=On, 4=Off. ROM operation should be just the opposite. 1=Off, 2=On, 3=Off, 4=On . At least that is the way I am reading the manual. The diagram does leave some room for guessing. This would explain your initial thought that the processor is running a completely different program! Let us know how you do with this.

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Make sure that you have identified your PLC correctly. It's easy to mix-up a C20, C20P or C20K PLC. C20 Operationa Manual @ MrPLC.com

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Hi guys! I checked the memory chip and its 27c256/15 which is an eprom. the DIP switch settings are ON-OFF-ON-OFF. I tried the other way round but still nothing. I switched off the system, disconnected the battery for some time but then when I restarted the system the PLC gave an alarm/error (fixed) indication. What could be the problem? Please help me as my job is at stake. Thanking you. bagi.

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Do you have any programming devices (handheld or computer) to check what the error is? Handheld would be a 3G2A6-PRO15-E (horizontal) or a 3G2A5-PRO13-E (vertical). Computer option would be SYSWIN software with a host link unit 3G2C7-LK201. Note that CX-Programmer does NOT support the C20 or C__K processors. Make sure that the dip switches are set for an eprom (see above). If the switches are set for Ram and there is no program on the ram after disconnecting the battery, the error could be NO END INSTRUCTION. The eprom should have the entire program. Hope this helps!!

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Great to hear from you gtsuport I do have syswin, but unfortunately, not the host link. I recently bought one from ebay and I'm eagerly waiting for a reply from the seller rchapa. Can you help me with this one: Is it possible to resart the plc without a programmer?

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It may be difficult with an error on the plc without knowing what the error is. Have you tried powering down the unit, changing the dip switches to the ROM setting and then reapplying power? If the ROM is good (should be, you just took it from a running system), that should reset the error and the unit hopefully will start. You will also need a cable between the host link and your computer. For this host link that will be a "standard" null modem cable. I am sure there is a cable diagram in the download section on this website. The Host Link will have a 25 pin female connector. Good Luck!

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The C20 PLC controls a dyeing machine. The DIP settings were always ON-OFF-ON-OFF and the memory chip is an EPROM. The CPU has RAM incorporated. Does anyone know the startup behavior of the CPU?

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Dear gtsuport, I powered down the unit, changed th DIP settings, and reapplied power but to no avail. It's funny that the dyeing machinES controlled by Japanese controlers, manufactured by a crap chinese company and bought from a crap hong kong company through a crap mauritian agent is now being saved by gentlemen from US. AND THE WORLD BLAMES THE AMERICANS

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Ok, based on your last post, I think this is what my be happening. I am checking with Jay to verify my thoughts. Based on the dip switch settings (see image below from manual, Thanks Jay!!) the processor is using RAM memory. I do not think that the C20 will transfer ROM to RAM. It would run on one or the other based on the switch settings. If the old processor had the switches set for RAM, then the program was in ram and that program MAY not be on the eprom. I really have no way to verify that guess. Will the old C20 unit still power up? Hopefully it will. When you get the host link, you may need to pull the program from the old unit and load it into the new processor. I know this will take time that you do not have, but may be the only option. Also, please understand, the C20 has been discontinued for a long time. After this machine is running, it would be a good idea to look at updating the processor. Syswin will support CPM1 and CPM2 units which offer much more capability then the C20. Just a thought. Hope this will help.

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Thank you gtsuport and thank you Jay, Your support has been invaluable and I know that the solution is in Robert Chappa's hands. Unless I get the host link I'm a dead man. I wait till I get the host link and if ever there is any problem to reset the PLC I know I can always rely on you guys. I'll keep coming back to this post. Thank you again.

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