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zeeglen

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CC&BW

Old-timer who grew up with vacuum tubes and therefore have been amazed and fascinated by the many advances in the electronics industry since.


zeeglen

's contributions
  • 09.25.2014
  • Missing datasheet details can cause problems
  • "Remember the 7805/7905 problems?" I do remember an error in the 7905 TO-220 pinout, I think it was a NatSemi datasheet. One of my products had to swap 7905 pins onto the pcb - looked like the darn thing had to pee!
  • 09.25.2014
  • Missing datasheet details can cause problems
  • You pointed this out in a comment elsewhere (EETimes?), and again I got a good chuckle from that page 10 goof. I like your thorough power test philosophy, test absolutely ALL functions of your design. A very accomplished mentor once told me "Don't ship your design until you are happy with it, no matter how much the boss whines about the schedule."
  • 09.25.2014
  • Missing datasheet details can cause problems
  • "Sounds like a serious simulation chore!" Made a small attempt, no LT1640 in my LTspice library so used a similar device. Not well versed in LTspice, but I believe it sets all voltages to zero at the start which makes simulation meaningless. It would be possible to set timed voltage sources to simulate a pre-charged capacitor, but that assumes knowledge of the problem ahead of time. Not surprising that the simulation showed proper functioning, I don't think any version of Spice can simulate a power-off condition. Power on is an assumed parameter. I could be wrong...
  • 09.25.2014
  • Missing datasheet details can cause problems
  • Interesting story! I vaguely remember a circuit from way back that I had to include a SCR to ensure a capacitor was discharged at power off, or else it would not power up again. I forget the details.
  • 09.25.2014
  • Missing datasheet details can cause problems
  • Could not find a Cload - I think it was probably on another card on a different backplane connector - which of course removes Cload when the fan tray is pulled out. Good observation on the job of C2, and I must admit I had not dug deep enough at the time to consider this aspect. The waveforms in the data sheet show constant gate voltage; since there is no dV across C1 there is no current through C1 - the 45uA current from the CURRENT (not voltage) source can only pass through C2 which does have a dV across it.
  • 09.25.2014
  • Missing datasheet details can cause problems
  • @BuzzBill Sounds like you experienced similar. Maybe a diode to discharge C1? Never tried; this was not my design and was not about to try to fix the problem without test access to the entire system which was not available to us. We just told the customer that we did not want to take on any repairs of this product. And as you probably guessed, the capacitor was surface mount ceramic with no value markings.
  • 05.23.2014
  • Milliohm Squawker great at finding shorts and reverse engineering PCBs
  • gordonbrush . com Give them your required dimensions and size of mounting hole(s). The 3 mil diameter phosphor-bronze bristles are held in a crimped-flat copper tube, they can figure out how many bristles needed to fill your dimensions. You do need to use heatshrink to support the bristles and keep them held together.
  • 07.18.2014
  • Could your product be exempt from EMC testing?
  • Wondering if the model rail Digital Command Control (DCC) bit rate of about 8620 Hz to the rails was chosen to be just under the 9KHz exemption? Of course modern decoders use a higher frequency for motor PWM and are not exempt, but maybe the original system designers were concerned about putting digital square waves to the "antenna" formed by the railroad tracks in a Class B residential environment.
  • 05.23.2014
  • Milliohm Squawker great at finding shorts and reverse engineering PCBs
  • I once worked at a place where the technicians (and managers) swore by their Huntron Trackers. Until the day when a tech could not figure out why a power module would not work. The tracker told him the output filter cap was good. I showed him that an ohmeter revealed the filter cap had 40 ohms internal leakage. My oft-repeated adage 'Never trust a Huntron' stayed with him after that.