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Testing DB9 Serial Functionality

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Use a multimeter on each end of the wire in question.
There should be a continuity setting that beeps when the connection is made.
 
ATMINSIDE said:
Use a multimeter on each end of the wire in question.
There should be a continuity setting that beeps when the connection is made.
Click to expand...
Thanks for the suggestion.

My understanding is that the continuity test only measures that a circuit exists (is closed) and does not measure the condition of quality of the circuit.

I do not believe that my multimeter has a continuity test setting. There is a resistance measurement setting, though.

Presumably, if continuity can be verified, I should then test the port at various data rates. Perhaps connecting a a DB-9 Serial cable between two computers and sending files between them may work.
 
zzzzzzzzzz said:
Thanks for the suggestion.

My understanding is that the continuity test only measures that a circuit exists (is closed) and does not measure the condition of quality of the circuit.

I do not believe that my multimeter has a continuity test setting. There is a resistance measurement setting, though.

Presumably, if continuity can be verified, I should then test the port at various data rates. Perhaps connecting a a DB-9 Serial cable between two computers and sending files between them may work.
Click to expand...

Yep, use the resistance settings, it should read ~1 ohms.
TBH, if it reads ~1 ohms it's more than likely able carry the full data rate.

Hehe, I haven't seen a DB9 in a awhile :)
 
Do a resistance test. While you're hooked up, wiggle the cable around. If the resistance doesn't jump wildly the copper is intact.
If the copper is intact, there is no change in signal quality.
The serial cable doesn't care in the slightest whether it's bent/kinked/filed-down-to-a-hair's-width-of-copper, as long as it conducts it's happy and any data rate will work.
 
There seem to be two pinouts for RS232 headers. If the wire 9 is broken, it would either disconnect the ground and not work at all or unreliably or disconnect the ring detect signal which is rarely used anyways. (You'll only notice that if you have a device that actually uses the ring detect signal, like a modem used for dial in.)

And of course, if you use a cable with the wrong pinout, it won't work.
 
Thanks for the replies.

I have not yet tested the cable. More important problems came to manifest (such as failing storage devices) and have taken priority.
 
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