Serial Port TZ3: Loopback test sounds good, but...

[Aristarco]

I haven't checked out the ports with a loopback tester, but I ran MSD and the Ports are reported active and healthy. I get a &quot;16C550 UART&quot; message, and all the usual suspects (RD, RTS, CTS, etc) reported as well behaved. I used my DVM and found the voltages on the TX and RX pins to be -12V and +2V (not the +12V as expected). And this happened in all three Motherboards, so I assume the Power Supply is guilty. Sometimes -12V go down to -7V. So I think I found the problem. Thanx 2 All for interesting on this somewhat obscure mistery.<br><br>Aris.

 

[edfair]

The -12v on TX is correct.&nbsp;&nbsp;the +2 on Rx is ok as it is floating with nothing going into it. At this point you have no symptoms of power supply problem that I can see unless the -12 is floating with nothing going on with the computer.<br>Better test would be to get it into setup mode and see if the voltage fluctuates on Tx. You never know what is transpiring once the operating system is up. There could be some timed program sending something to the serial port causing the Tx to change.<br>Normal voltage on Tx is -12, transitions to +12 for a start pulse, data pulses are square waves to -12 and return, and stop bit takes it back to -12v.<br>And try the loopback plug. Thats the only thing short of real data that will massage the Rx. <p>Ed Fair<br><a href=mailto: > </a><br><a href= > </a><br>