Modem Jacks Reverse

[Gloryhound]

Scenario: User's computer is plugged unprotected into phone line during lighting storm. The following day modom gives error, no dial tone. On a hunch I did something very un-techy. I plugged the line into the PHONE jack. Tried it and to my surprise it had worked. I didn't get bumped off could check e-mails and everything else. The unit seemed to be functioning properly.. In reverse. Can anyone explain this to me? Am I missing something obvious?

 

[InnoTech]

well, that would obviously depend on the modem type. however, either way it is a very wierd thing.

"Jack of all trades. Master of none."

 

[pansophic]

Some of the lower-end modems that I have worked with, like the Zoom, don't actually differentiate between the two jacks. Most actually have a relay between the line and the phone, so that the phone cannot be picked up to interrupt a dialing session.

But I had never guessed that they might have independant overvoltage circuitry.


pansophic

 

[G0AOZ]

Maybe the current surge through the changeover electronics welded the internal modem contacts to the phone jack connections...

User is lucky that computer has not been fried!


ROGER - G0AOZ

 

[Gloryhound]

Well I took the modem out anyway and examined the circuitry, there are a few surface mounted resistors that are fried and one is vaporized all together. Yes it is a cheap modem Aopen 56K - PM The phone and line in jack seem to share circuitry on the board and how it got fried so that it could work this way is simply a fluke.

 

[PaulAlexander]

Hi all,

I fully agree with the explanation of GOAOZ that the current surge could affect the modem circuitry!
It is also highly possible to affect some Electrolytic capacitors, which when their voltage is measured after the lighning it might take as long as few hours to totally discharge and return to their normal condition! In which case the modem might start working again!
However the probability of this happening is a very slim one!! Why? Because simply in most cases the modem circuitry whould be in a state of "fried chips"!!
But even then, if the current surge has incapacitated few non important resistors not affecting considerably the circuit tracks all the way to telephone jack, the modem could still make it! But the question is for how long?
No one can answer this!
Only Gloryhound will let us know. Let's hope that it will never be needed to do!