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scottmurphy

CQM1H-PA203

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We had a PA203 go poof today, it was to much of a coincidence not to be related to what we were doing. The setup is as follows: PLC 1 CQM1H-PA203 CQM1H-CLK21 CQM1H-CPU51 CQM1H-SCB41 CQM1H-ID212 x3 CQM1H-OC222 x2 CQM1H-AD042 x2 PLC 2 CQM1H-PA203 CQM1H-CPU21 CQM1H-ID212 x8 CQM1H-OC222 x2 PLC 1's Controller Link Network is linked to a PLC in another area, the above 2 are in adjacent cabinets. These 2 are also linked via the 1:1 data link, with the CPU51 being the master. What happened today, was that we brought the PLC 2 online for the first time. This went ok, with no issues. What then happened, is that I enabled one of the outputs of PLC 2, which we are 95% sure that there was no power applied to. Then, PLC 1 shutdown. Upon investigation, we found that the AC supply to the PA203 was still present. So we removed the PA203, opened it up, and found that the internal fuse of the had blown. Being good studious electrical folk, we replaced the fuse and re-installed the unit, and it did not work. It looks like there was a 'splatter' mark on the underside of the PCB, again too much of a coincidence. It seems that the PA203 blew a bit more than the fuse. So, first question, finally, before we send the unit away for repair, does anyone have a circuit diagram of the PA203 so we can attempt to repair it ourselves? Second question, how could this have happened? My initial thoughts, were that there was some sort of polarity mis-match between the 2 PLC's. Both have the same DC supply, but, I am almost sure, that the output module did not have any 'common' power applied. Third, I was under the assumption that the PA203 supplies the 'backplane' or installed modules only, no IO or field devices at all. On that theory, then by energising an output, it should have no impact on the other PLC's power supply. Unless of course, that the PA203 is supplying power to something else that is connected wrong, but from what I can establish of the Unit manuals, there is no link between the PA203 and any external devices. Or, was it just coincidence?

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That seems the classic case of FINSTB moments F### Iv'e Never Seen That Before

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I love them anagrams from across the ditch. Definitely an odd one, further investigation, MEN link not fitted at local supply, possibility of brown out etc. Will put UPS on supply to both PLC's. Don't want it to happen again There is the off chance that it was a coincidence..... But, since the PLC 2 had just come online, after sitting idle for years, and the first time an output had ever been switched, could of caused an increased load on the PA203, causing a fluctuation on the incoming supply, with the PA203 of PLC 1 wearing the result? I am only speculating here, trying to establish a cause...

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Are you running a shielded cable between the PLC;s... Only connect shield to one end. I wouldn;t want any earth loops going between the PLCs... BTW do the comm;s ports still work on both PLC's ?

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Shielded comms cable? Do you mean the 1:1 datalink cable? It is a standard 1pair screened, I think that it has the foil shield. The comm port on PLC 1 still works, didn't try PLC 2 yet, will do that also.

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You need at least 3 cores... TXD RXD and SG to work.. ( 2 pair ) With the foil shield, more then likely there is also a trace wire which of course is the shield... and this might be connected to the shell of one of the connectors (some times).

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Sorry Sleepy, it also has the drain wire through the middle, the type that is normally used for analogue signals.

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You may be pushing the limits of the PA203 on PLC 1. Its output rating is 3.6A @ 5VDC and the load of all of your CPU and modules adds up to 3.605A maximum. A fluctuation in supply power may have been the last straw, but I would think it would have only blown the fuse in the PA203, not cause a splatter. Kind of a mystery. If you do replace the PA203 I would upgrade to a PA206 to be safe.

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From what I have seen with the power supplies, when they reach critical mass things tend to melt. Definately get a larger supply in there. I always shoot to have about 35 to 40% extra just in case. Also, if they have been sitting, you probably had some "SALT CORROSION" as I know it, going on. That is where you get condensation and it dries, condensation and it dries repeat this daily. After a period of time, the condensation attracts dust and dirt. When the moisture evaporates, the dirt and dust stays behind and build carbon paths. When combined with electrical energy, they tend to cause rather spectacular pyro-technical displays. When inside a power supply case you only get to see the aftermath where the smoke was let out.

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I have just done the calcs myself again, and ECSI is bang on the money, I am pushing the limits of the supply for the PA203. I actually did this for the other PLC a while back when adding modules, and thought that I was within tolerance, but I made a mistake with the OC222 module.

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