I think it may be possible for a bad combination of software and
cable/device to burn out a parallel port. For example, if the UserPort
software happens to hold a particular parallel port output signal high, and
the device at the other end holds the same pin low, then you get a short
circuit. This could also happen if the cable is constructed incorrectly and
two output pins of opposite polarity are tied together. In this case, one of
the three (software, device or cable) is probably not adhering to the
parallel port I/O spec.
The caveat here is that I don't know whether the LPT port spec is designed
to tolerate short circuits. I do know that the RS-232C serial port
specification specifically calls for all pins to tolerate shorts. However,
even the LPT spec has the same requirement, it's possible that certain
manufacturers (perhaps DELL) don't adhere to the spec.
Another possibility is that a design or construction error in your keying
interface circuit could damage an LPT port by shorting the CW output pin. In
this case, even if the LPT spec calls for tolerance of shorts, the spec
would undoubtedly call for tolerance up to a certain current flow (the
RS-232C implementation uses current limiting so shorts can be tolerated.)
Your keyer interface could permit greater current flow, leading to damage in
the event of a short.
Yet another possibility is RF leaking into the LPT/keyer circuit. If the RF
is strong enough, it could cause a short in the LPT interface.
73, Dick WC1M
> -----Original Message-----
> From: kk9a@arrl.net [mailto:kk9a@arrl.net]
> Sent: Tuesday, May 27, 2003 3:39 PM
> To: 'WriteLog'
> Subject: Re: [WriteLog] RE: User Port appears to have
> destroyed a DellInsprion8100
>
>
> I find this story very interesting. I recently purchased a
> Dell Dimension 2GHz with the Windows XP Pro operating system.
> I installed Userport and plugged in a parallel port keyer
> and it appeared to work well, until my first contest - the
> 2003 ARRL CW Contest. Somehow the Dell parallel port burned
> out just before the start of the contest and I had to operate
> the contest using an old Toshiba laptop. Dell came to my
> house and replaced the motherboard which fixed the problem,
> but I'm afraid to use it. I also have a SIIG PCI parallel
> port on the computer so I just purchased Direct IO which
> allowed me to access both parallel ports. I operated the
> WPX CW contest
> last weekend using my PCI port (LPT 2) with no problems.
>
> 73,
> John KK9A / P40A
>
>
> ----- Original Message -----
> From: "Barry Merrill" <barry@mxg.com>
> To: "Writelog@Contesting. Com" <writelog@contesting.com>
> Sent: Tuesday, May 27, 2003 17:07
> Subject: [WriteLog] RE: User Port appears to have destroyed a
> Dell Insprion8100
>
>
> This is an update to my April 5 posting of this same subject.
>
> When I reported to Dell Technical Support on that Saturday
> that the machine would not power up at all, instead of
> getting an expected RMA to return the 18-month-old notebook
> for repairs, Dell immediately sent me an Inspiron 8200
> notebook (1.7GHz vs 700 MHz, bigger hard drive, with
> Windows/XP vice 2000!) that arrived on Wednesday morning!
>
> But before again trying UserPort and the LPT keying circuit
> and burning up the new 8200, I spent the last six weeks
> trying to get someone at Dell in technical support who
> understands their power systems that could discuss what might
> have happened, to no avail. It turns out that the old
> machine I sent back is never going to be examined by anyone
> at Dell; it just goes to a warehouse, and my detailed note
> attached to the machine to request an explanation will never
> be answered; and my point-of-contact replacement-sending-guy
> could care less as to why it failed, since his job is only to
> get me the replacement machine.
>
> So yesterday I installed User Port software on the new
> Inspiron 8200, then plugged in the (same) LPT Keying Circuit,
> and it works perfectly!
>
> I first went to Control Panel, System, LPT section, to see
> what IO address are used on this system, then started User
> Port, deleted all default addresses, and typed in the
> 03xx-03yy range from the control panel.
>
> So I must now assume that there was some other defect in the
> Inspiron 8100 hardware that caused that pop and smoke
> immediately after plugging in the LPT Keying circuit, after
> starting User Port, so I withdraw my accusation that it was
> User Port itself that caused the old machine to die, and I
> can now confirm, as have many others, that you can use LPT
> Keying with Windows XP and User Port software.
>
>
> Barry, W5GN
>
>
>
>
>
>
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>
>
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