Stupid Mistake

I have just been testing a new version of my four toggles PCB that does phantom, pad, mic/line and phase switching. It is the same schematic just with the switches arranged in a square instead of in a single column. To aid wiring up to it I had marked the hot pin on the 3 pin Molex connectors I use to connect mic, line and the output. Wired it up and odd things happened. Mic/line switch did nothing - mic signal still came through. 20dB pad did nothing but phase switch reduced level by about 6dB. Realised I had left some component soff the PCB. Fitted and retested - very similar results. I began to suspect I had made a mistake in the PCB layout so go back to computer and load up PCB layout onto screen. Carefully check all traces - nothing wrong. Peer at PCB layout for about half an hour and then it hits me. I had rotated connectors at some point to ease tracking but I had not moved the silk screen letter H used to indicate which pin was hot. The H was next to the screen pin!! Rewired the test PCB ignoring the 'H' and it all works perfectly.

Cheers

Ian

Perhaps it’s ‘H’ for HEARTH 

Thanks for sharing this Ian.  To quote your signature line: 'The only people not making mistakes are the people doing nothing'  Being able to share your mistakes so that others may learn from them is a noble character trait. 

If testing with phantom and an expensive mic could have been an expensive mistake...

Noted, check silk screen (and code comments)...

JS

joaquins said:

If testing with phantom and an expensive mic could have been an expensive mistake...

Noted, check silk screen (and code comments)...

JS

Click to expand...

Been there, almost done that. I had a miss wired phantom connection on a PCB so phantom was always on. This blew up the op amp output stage of my test set - fortunately the manufacturer had included fuses for this so it was not as expensive as I first thought. SInce then the test set is always few via transformers.

Cheers

Ian

Take comfort you didn't recently make a PCB and forget to mirror the non-symmetrical part to bottom layer...

boji said:

Take comfort you didn't recently make a PCB and forget to mirror the non-symmetrical part to bottom layer...

Click to expand...

I have done something similar. I designed a small PCB, about one inch square to make a right angled PCB socket for by  my new 35mm modules. I then designed a new version of my classic PCB, replacing the existing tube sockets with this new  right angled one. Somehow I got the holes on the PCB the wrong way round; 9 to 1 instead of 1 to 9.

Cheers

Ian

  On a quite bitchy board to self etch (as I still do as delay times here are prohibitive) I successfully etched a PCB containing an 0.5mm pitch 30 pin part, in the printing process the image got shrunk by  ~3%. Aligning the first pin with the first pad would make the last one to be on the space between the two pads, I'm about to re-etch the thing.
  I use toner transfer, but I got a laminator which makes things so much much better than the iron, I don't even think in going to photosensitive/exposure mess.

JS