PI update

[Carl]

My radio receiver chip came in at work, so I've had little time for anything else the last couple of weeks. However, on the PI design I had been wrestling with a strange coil pulse phenomena that defied explanation.

Basically, I was getting a negative overshoot on the coil waveform during flyback, as if the coil was slightly underdamped. I tried several different damping resistor values, and could change the overshoot, but could not make it go away. Well, last night I thought, "maybe it's the o-scope," so I switched the probe to the B-channel and the problem went away.

So, it looks like the design is final, and once I make a couple of tweaks to the PCB I will send out for some boards. Sorry for all the delays.

- Carl

[Russ_NY]

Re: PI update

Carl,
Thats great that you found the problem. I know how it goes to be led off on a tangent due to test equipment quirks. I found that some if not all of the problems I was having with the circuit were due to what appear to be switching transients somehow getting onto both of the -5 volt supply lines. I had checked the supplies thoroughly early on and they were clean,, but as I added additional circuitry something started causing the problem. I havent isolated the specific cause as yet, but running the entire circuit off of my bench supply has helped considerably. Family commitments have preempted my bench time the last few days, but I hope to get some time to work on it today and thru the weekend. I sure would like to see your final schematic.
Thanks
Russ

[Randy Seden]

Re: PI update-Funny Story 4 U Carl

Carl,

Back in the 70's I worked for a Heart Pacemaker Company and there was this old salt of an Engineer who was a bit of a pracical joker. Turns out he had this little magnet that he would stick in an O'Scope of a fellow Engineer when they would walk away.

Well, this one poor fellow was working on a amplifier and couldn't figure out why he was getting the response he saw, mean while Russ (the joker) was standing back quietly snickering. He of course would let us tech's in on it and we too would walk by real slowly in the hallway watching this poor guy try all sorts of things and before it got too far Russ would end it.

Randy Seden

[Russ_NY]

Re: Must have been a different Russ (off topic)

About the worst trick I ever did was using a sig gen to jam a fellow tech's radio who insisted on playing his favorite station all day every day. The other technicians in the lab were quite happy to be rid of it also.
Russ_NY

[Carl]

We're a bit more brutal around here...

In the old lab we had wall outlets with a light switch control, so we could power up/down all the test equipment at once. A couple of times we pulled the outlet cover and wired in an electrolytic across the 110v. The unwary bench user would come in and flip the switch, and jump across the room at the loud POP and sparks coming out of the outlets.

Another favorite is to sneak-solder a 10-ohm resistor across the supply of a test board. When the user turns it on, he gets smoke and stench, and a feeling of having trashed the test board. This is especially effective on young co-ops.

- Carl

[Dave J.]

more scope shennannigans

An engineer I used to work for told me about a stunt he and some buddies pulled back in the 60's.

The engineering manager had to leave early one afternoon. So.. the other fellows dismantled his scope, pulled the CRT, installed a 300 watt floodlight in its place, and put it back together.

The next morning they brought him a prototype of his that they said had quit, and asked him to scope it to see what the trouble was.

--Dave J.