Damage To Serial Port

[Spedley 0]

Is it possible to damage a laptop's serial port by plugging into an SLC5/04 or PanelView serial port becuase that's what seems to have happened?

[panic mode 246]

it is unlikely if the other side is also RS232 port. RS232 specs says that ports should tolerate any signal (voltage, short circuit...) within speced limits (early specs mentioned voltage signals of up to +/-25V) without damage. there are some devices that use some pins for other things like power etc. also i don't think i've seen any default RS232 with optical isolation so technically it is possible to inflict some damage. but before you throw your laptop away, are you sure that problem is not soemthing else (maybe you installed PIC driver for RSLinx for example - this replaces standard RS232 driver so to use it as RS232 you have to roll back your drivers, maybe something else was installed and keeps RS232 port busy like ActiveSync. etc.). You can try connecting to any other device that used to work or test port with hyperterminal and simple loop back adapter (or crossover cable such as 1747-CP3 and another port - even if it is on another pc).

[TimWilborne 108]

I have heard of bad grounding techniques damage the serial port. Pretty much you end up with power coming from the PLC on pin 5

[Spedley 0]

I haven't checked the laptop personally but I've been told that it sends data but does not receive it (or perhaps the other way around) which would make sense if power went into pin 5. I'll make up a cable and check for bad ground/excessive voltage/current. Cheers!

[TimWilborne 108]

Plus look at the simple stuff. Is the cable good? Was someone in a hurry cramming the cable into the serial port of the laptop and bend the pin maybe?

[Spedley 0]

That someone was me. I wasn't in a hurry although I was on the tired side. I was backing up several machines before the mains transformer was changed, SLC5/03's, SLC5/04's PV550's with DH485 and DH+ and just serial connections. I had a PIC box, Female-Female Serial cable, Gender Changer and whatever cable was connecting the PV to the SLC. I did just try each cable until it worked which was perhaps not the best method but it should not have damaged anything. All cables and pins are good, I'm sure its the SLC or PV.

[DanW 41]

There a technique known as a "loop back" test where data sent from a port loops back and is seen as received data on the same port. You could make an adapter for your serial port with solder-type D connector (from Radio Shack) and connect Tx to Rx. Then put the adapter on the COM port and use a terminal program like hyperterminal to see if what you send comes back. Dan

[Sergei Troizky 26]

I would recommend to open the computer and verify the connector soldering to the PCB. I've seen couple times broken soldering on heavily used service notebooks.

[Spedley 0]

I thought I'd tell you all someone found the problem. The machine has a plug-socket to plug in your laptop etc, however it is not normally used and does not cause a problem. Apparently the plug-socket is on a different phase to the rest of the machine which can cause votage problems. Electroncics it's not my field but that was the explination I was given by the person who replaced the laptop.

[Sergei Troizky 26]

The Mitsubishi SC-09 programming cable package includes the paper insert which directly forbids powering the PC from different phases than the PLC. They call this "phase conflict". I've experienced this couple times and the PLC was damaged as well.

[TimWilborne 108]

I'm having a hard time grasping this one. Especially on 230VAC it is not uncommon to have the PLC and PC on different phases. I would still think it would have to be a grounding problem but I'm not in the electronics field either. Now that I think about it a little more, even on a 480VAC fed machine it would not be hard and chances are greater that they are on different phases. That same 480VAC that is feeding your machine is ran through a transformer to feed you receptacle panels that your laptop would be plugged into. The way I am seeing it you only have a 1 in 3 chance of matching the phases.

[Spedley 0]

I quite agree with you there TW but I suspect the problem lies deeper because the machines are having new cabinets made which adhere to current safety laws.

[TimWilborne 108]

The more I think about it this is just an excuse from a computer repair guy who couldn't figure out what was wrong so blamed it on magic. Usually the magic is called lightening but I guess the skys were clear. I have a little PLC I play with sometimes at the house the plugs into a 120VAC wall outlet and my laptop is normally plugged into another wall outlet. I plugged my voltmeter in between them and got 220 Volts. You have a 50/50 shot in a house in the US and a 1/3 shot in a 3 phase plant of lining them up. I am thinking that a house or small business in England would only have a single phase of 220 so do you think that he just wasn't that familiar with 3 phase power? He's full of it Edited 23 Apr 2006 by TWControls

[Spedley 0]

He knows what he's talking about, he's the guy who is replacing the panel. The machine is a large press (1 of 7) and pulls about 280 amps. It's not a small company, infact it's a large American Company. What is the power supply in the United States? In the UK we have 3 phases of 240V giving a 3-phase voltage of 415V (I think) although the 240V is usually more like 230V and it varies depending on demand. I'll ask more detail next time I see him.

[Smoke 0]

Are comparable 3-Phase is 480VAC @ 277 per-phase. You might want to add a small UPS to your cabinets to prevent the same thing happening in the future?

[TimWilborne 108]

Our low voltage is 240VAC (3 phase 120VAC) and our high voltage is 480VAC (3 phase 277VAC). I have never heard or seen a phase conflict causing this. I would like to hear a little more of the explanation. Was there any mention and differential of grounds or anything like that? That sounds like more of the explaination and can be caused by two separate supplys ("phase conflicts")