Idiots & power supplies - RF Cafe Forums

 Post subject: Idiots & power supplies

Posted: Tue Sep 08, 2009 10:10 am 

I had a customer call me the other day to tell me what piece of s@!%*^ my company's amplifier is because it had such terrible IP3 performance. I ran through the usual list of questions about how she was testing it - power supply, coaxial cable & connector integrity, spec an setup, etc. All seemed well, so I dared to ask about following ESD precautions and caught an earful for impugning her skills as a lifelong technician.

Just as I was about to give up and send a replacement (and have to admit as she implied that, yes, I was yet another male that cannot admit being wrong), I remembered her reading off the power supplies being used. It was two 6V supplies in series that had a 6V center tap to a separate controller board. After a little more questioning, I figured out she had the negative line of the PA plugged into the center tap of the two supplies, but was measuring the voltage with the DMM connected between the ground reference and the second series 6V supply. So the DMM read 12V while the PA saw only 6V.

The coax cables didn't pull the PA reference to ground because the DC connections are isolated from the case. Kind of a strange situation, but it's one I'll be sure to ask from now on.

_________________
WLAN Installer

 Post subject: Re: Idiots & power supplies

Posted: Sat Sep 26, 2009 10:12 pm 

I've had phone calls like that.

It reminds me of a story I read years ago about a software engineer who had worked on a database program and he got a phone call from some programmer customer who was having trouble following the instructions. The story was from back in the early days of computers. Anyway, the customer wanted to know how to enter the "less than" key that was called for, and vehemently insisted to the engineer who wrote the program than there was no such key on the keyboard. He got downright abusive and felt the need to relay his impressive credentials to the poor sap trying to help him. I don't remember exactly how that story went, but it ended hilariously when the engineer finally had to tell the guy to find the comma key and then press Shift along with it to get the < symbol. He wrote that the phone went silent at that instant, and the customer hung up, never to call back again. The customer had suddenly realized what a fool he had made of himeself. The actual story was a lot funnier. I'll try to find it and post it.