PLC with no output whatsoever  - Page 1
Forum section: electronics / repair

author: Susovit
author_rank: Newbie
timestamp: March 03, 2023, 04:48:29 pm
content: I have a Mitsubishi PLC with transistor type output. The problem is that none of the output is turning on, not only output. The output indicator LEDs aren't showing up too. There error led is not glowing. What can be the problem. I know it the plc has a output side hardware problem because the software is showing the proper outputs. What can be the culprit.?Please help

author: R-1125F
author_rank: Regular Contributor
timestamp: March 03, 2023, 09:41:46 pm
content: What is the model number and what testing have you done?

author: coromonadalix
author_rank: Super Contributor
timestamp: March 04, 2023, 02:35:56 am
content: was it working before or it is a replacement ??

author: Susovit
author_rank: Newbie
timestamp: March 04, 2023, 07:10:56 am
content: It is a Mitsubishi Fx3SA mt.it was working fine few days ago.I accepts input. Input LEDs light on as I give input. The hmi shows the proper outputs when I test it in manual mode. The output LEDs and the outputs however doesnt work at all.

author: JimmyJo
author_rank: Contributor
timestamp: March 04, 2023, 12:43:34 pm
content: Have you opened it? It's not uncommon for PLCs to have input output sections individually fused.

author: R-1125F
author_rank: Regular Contributor
timestamp: March 04, 2023, 01:07:40 pm
content: See if the fuses are good.Also, have you checked it using the PC software?

author: BMK
author_rank: Regular Contributor
timestamp: March 04, 2023, 01:15:37 pm
content: Please clarify..Are the LEDs for the outputs not turning on?On that model, the LEDs are on the logic board. The IO board is separate PCB. Very unlikely that a hardware problem or fuse on the IO board could result in LEDs off. If you have no LED, then your user program is not trying to turn on the output.... There are 2 likely possibilities..1) An MCR instruction in the program is denying outputs. Usually as a safety measure. Check all inputs, especially those related to stop buttons/interlocks etc..2) Program is lost. Yes, the Run light will happily light up if user program is empty...Do you have programming software, or do you rely only on the HMI?

author: Susovit
author_rank: Newbie
timestamp: March 04, 2023, 01:53:46 pm
content: I relied completely on HMI. The software could not be accessed due to password lock.The plc had a blown power supply side when I checked. Output lights are not turning on.Run light is coming. Due to password, I think program is ok.I have attached some photos.

author: Susovit
author_rank: Newbie
timestamp: March 04, 2023, 01:55:01 pm
content: Quote from: R-1125F on March 04, 2023, 01:07:40 pmI think the output section is completely out. Can that be possible without the CPU being damaged?

author: Susovit
author_rank: Newbie
timestamp: March 04, 2023, 01:56:47 pm
content: I think output side is damaged but can't trace how.

author: Susovit
author_rank: Newbie
timestamp: March 04, 2023, 01:58:58 pm
content: I have used manual mode to turn on individual outputs from hmi. But the plc output LEDs won't come on. However, the hmi displays on properly.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 04, 2023, 02:17:47 pm
content: not sure if its themBut some plc even with the software have an hidden memory range / section, the programation goes in there and will ne be accessible for retrieval, even with a password ...had a similar one in a pcb oven, and for sure the maker re-sold them to us at twice the price, still not aceessible by any meansthe plc may have suffered more damages than you think, maybe its time to change it, and yeah you face the programming problemis your equipment serviceable ? suppport tech ?

author: R-1125F
author_rank: Regular Contributor
timestamp: March 04, 2023, 02:20:32 pm
content: Check the basics. See if there is 24v and 5V measured on the output board.

author: BMK
author_rank: Regular Contributor
timestamp: March 04, 2023, 02:22:30 pm
content: Quote from: Susovit on March 04, 2023, 01:58:58 pmThis really tells you nothing. Depends entirely how the machine builder programmed it.. HMiI buttons likely just linked to memory bits. I strongly suspect you have lost the user program.To rule out hardware problems on the PSU/IO board, you can swap logic board into new PLC.Password on these is easily defeated by monitoring serial Comms on the login process. The password is sent plaintext from the PLC to the programming software. The check happens at the PC side!

author: BMK
author_rank: Regular Contributor
timestamp: March 04, 2023, 03:09:19 pm
content: Damn, I'm old. I had to resort to the waybackmachine to get this:https://web.archive.org/web/20050118130110/http://freespace.virgin.net/ian.sullivan/mitsubishi.pdfSimpler times.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 05, 2023, 02:44:11 am
content: ill be da.... lolljust found this forum, but have very old threads and recentshttp://plcforum.uz.ua