Good guess, but it turned out to be a bad protection diode placed on the input of the 4049. The pulse is actually closer to 5 volts, but was being loaded down by the partially shorted diode. Mystery solved! It is still a bad design.
----- Original Message ----- To: "Multiple recipients of list CHIPDIR-L" <[EMAIL PROTECTED]> Sent: Tuesday, November 18, 2003 1:34 PM > Hi Syd! > > Is that 2V at the input of the CMOS chip? That's definitely too low. > The threshold level for CMOS lies at 50% Vcc or in this case 2.5V. > Driving the input with less than this will at best drive the CMOS into > the linear region of operation. What I could imagine here is that the > input of the 4049 (possibly the ESD protection) is toast and poses a > too low resistance to the driver from the other board... > > Uwe. > > > SLA> The trigger pulse is generated on a different board, then is conditioned > SLA> with a 4049 cmos chip. It seems weak, but there are so many other problems, > SLA> I am having trouble figuring out what it is supposed to look like. The 4049 > SLA> is powered by a separate 5 volt regulator, but the input to it is only a 2 > SLA> volt pulse, which seems too weak. > >> > >> How is the trigger pulse generated and what does it look like right > >> now? If the original MOSFET was shorted, it probably also shorted > >> either drain or source to the gate. This might have killed the driver > >> circuit either by overloading it (short to ground) or by bypassing the > >> high voltage pulse directly into the driver.... > >> > >> > >> SLA> the 840 with regard to the trigger pulse? Most of these type tools > SLA> use an > >> SLA> SCR; this is my first experience with a mosfet fired transmitter. > >> > >> > >> Uwe. > >> > >> -- > >> Author: Uwe Zimmermann > >> 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). > > -- > Author: Uwe Zimmermann > 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). -- Author: Syd Levine \(AnaLog\) 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).
