On Wednesday 25 December 2002 06:08, somebody wrote > Two thoughts come to mind. > > 1) Might the circuit somehow be oscillating? I have seen circuits of > this kind that would sing. The problem went unnoticed because > applying a meter or scope probe added enough capacitance to kill the > oscillation so everything looked normal. The fix was to apply a nf > or so of capacitance from the gates to ground.
These fets are directly driven by latches. There is smoothing in abundance > > 2) Could this be a RFI issue? Are there strong fields around, such > as a broadcast station in the neighborhood, that the circuit is > picking up and causing the FETs to turn on? I hardly think so. 2 of these work, this one works but loses 10mA. > > Fred Townsend > > Declan Moriarty wrote: > > Here's one to tease yourselves over. I have a board to fix > > and for once, I do not know how to go about it. > > > > I designed the thing. It's battery powered, and is consuming > > batteries. There is a 1.0V line with nearly 40 class B fet stages, > > using logic level fets (Irlml6401 p-channel on top and irlml 2502 > > n-channel underneath) The gates are tied; > > > > That stage is pulling 10 mA on no load. It should draw basically > > nothing. It draws 10 mA even with the load disconnected. The 'Off' > > condition has -1.5V on the gates; the p channel fet sees the > > voltage from +1.0 to -1.5V and is fully on, and the n channel > > reverse biased. 'On' it is the reverse - the p channel is reverse > > biased, and the n channel sees +2.5V. > > > > Now the tracks are too thick to use a millivolt meter and trace > > where the 10mA is going. 10 mA doesn't show - I had difficulty > > tracing 100mA. How do I find the $*�"! current leak?? > > > > I had one thing - a fet test program which applies logic 0 to all > > gates and will drive one at a time high, as I press buttons. I > > couldn't find any gate leakage. The 5V will usually leak onto the > > 1.0V if a gate is gone, and I can find the fet pair that way. I > > will go around the fet pairs with a voltmeter and check the values, > > but expect to find nothing. > > > > -- > > Regards, > > > > Declan Moriarty. > > -- > > Author: Declan Moriarty > > INET: [EMAIL PROTECTED] > > > > Fat City Network Services -- 858-538-5051 http://www.fatcity.com > > San Diego, California -- Mailing list and web hosting > > services > > ------------------------------------------------------------------- > >-- To REMOVE yourself from this mailing list, send an E-Mail message > > to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in > > the message BODY, include a line containing: UNSUB CHIPDIR-L (or > > the name of mailing list you want to be removed from). You may > > also send the HELP command for other information (like > > subscribing). -- Regards, Declan Moriarty. -- Author: Declan Moriarty INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
