Reactivating Melspec F1-20MR

Hello. First time post and new to PLCs.

I acquired a Melspec F1-20MR which came second hand and an additional 24VDC power supply. I made a huge mistake the very first day and seeing the 24VDC on the input side of the controller, did just that! I imput 24VDC into the unit. And popped the power supply.

Mitsubushi would not assist me in what parts I needed to repair the power supply section and the transistor next to the rectifier diodes had exploded so I replaced it with one that met the specs along with the other components.

I replaced it, and found the Zener had blown as well so replaced that with a new 24V Zener. Reassembled the unit, switched it on and it went! I got one indicator light and a corresponding sound from one relay as per the program that would still be there from the previous owner.

But when I measured the output of the 24VDC I got 30VDC. The next time I switch the unit on, and run it, I got half color LED and (memory here) the voltage out of the unit had reduced to 16VDC.

Reading the manual I see the unit has a protection against overload and will automatically drop the voltage to an inoperable level which it has done.

I replaced the Zener as I believed I had purchased the incorrect one. Boom. 24VDC, I run the unit, and it is still in the overload state, immediately reducing the voltage to inoperable.

I am absolutely stumped how to reset the module and would like to get it running to see what is programmed into it already as it might do what I want it to already. It came with a couple of proximity sensors which I might use.

Questions:

1: Does anyone know how I might get this unit running again? Is it possible I should put a lower value Zener in the power supply and it might run again out of the overload state that seems to have latched?

2: Is it possible to reset the unit without having to reprogram it.

3: If I do reset the unit, what are the default settings?

4: Is it possible I can re-program the unit myself, do I just need the software and a dongle for my laptop?

Mitsubishi here in New Zealand initially responded, but then stopped returning emails when they realised I did not have hundreds of dollars to spend. I really just want to get the unit going and then perhaps look at programming it.

Please if anybody can help I would be most grateful.

Kind Regards
Boyd from NZ

I can only presume that you connected the 24v dc with the wrong polarity.
Because the F1 would actually work with 24v connected to the service supply.

I came across it a few times where there were no wires in the mains voltage terminals
but the thing was lit up and working. And in one case where the power board had failed
I put 24V dc on the service supply and it came back to life.

However, the F1 is so old now, probably over 25 years since they went out of production.
The software is DOS based and I don't think you can get the programming leads and interface for love nor money.

Try putting 24V dc on the service terminals - if that doesn't work you have a nice paperweight.

Hi. Actually putting 24vdc into the unit blew the NPN transistor, a cap and a zener. I now get 24vdc out of the unit. But as soon as I connect it to the "run" terminal it drops to 16vdc.

Are you saying to wack 24vdc onto the negative and "run" terminals so see it it fires up?

Remember, the very first time I powered it up with the wrong Zener it operated. It was the second time is went into that half state mode.

And really? They are THAT old? The guy in Auckland was happy to charge me hundreds to fix it. He should have told me that. I can buy a new state of the art one now that I can program myself!

Are you saying to wack 24vdc onto the negative and "run" terminals so see it it fires up?

Click to expand...

NO, just +24 to the 24v terminal and -0v to the 0v terminal. The power light should light up. Then linking the 24V+ to the run terminal the run led should light.

But by the sounds of it - it's a gonner.

And as I said, even if you got it going - you won't find the leads and special interface anywhere. Lots on here have asked before to no avail.

I have the manual programming interface - one has to copy program out by hand to paper after setting it to the correct PLC state F1 F2 etc.
Medoc is available but only runs under DOS or a DOS emulator that supports direct port access - The Special interface modules are hard to come by and never go for cheap
" NOW I WISH I HAD SAVED SOME OF THEM OR AT LEAST ONE...."
Hind sight

You may find many of the higher value electrolytic capacitors are either shorted or passing current causing load on the power supply - this is due to the significant age of the unit. This is one of the reasons many of these units are being replaced.