kidkv said:
can you look at this circuit and tell me if the caps CP202 and CP203
are right
http://www3.telus.net/public/a5a26316/WelderPDFs_Pics/TIGTIMING.pdf
and can you tell me why i am geting 0.71volts to Q205 and Q206 when the
2n3904 is geting 5volts
and if i put a lower ohm resistor to give more voltage the voltage from
the 74hct14 gos from 5 volts on the output down to 2 to 1 volts this is
what i can't get.....
Hate to say it, but this is a pretty crappy design:
(1) Using schmitt triggers as timing elements is not terribly keen--
the electrolytic capacitors tend to have wide variations in leakake and
capacitance. Also using monostables around BIG ELECTRICAL ARCS is not
very keen! They're likely to jitter all over the place. This type of
design really calls out for some digital timing.
(2) There are several boo-boos in the schematic, even at a quick
glance. One monostable doesnt have a pull-down resistor, unless it's
in the off-page link. Several of the coil drivers don't have
transient-clipping diodes or current-limiting resistors. The resistors
on the unused circuits are really bizarre. Feeding the unchained
comparator and even schmitt triggers from an off-page link is likely to
result in serious oscillations. I don't see any power supply bypassing
capacitors.
I'd give this circuit design a grade of about D+. It might just may
work under ideal conditions, but it's unlikely to work well and
precisely without some tweaking.
It reminds me of quite similar control board for a $3000 tape recorder.
Under low-humidity conditions, the audio tape would build up small
static charges-- you could hear them discharging to the metal guide
posts with a very faint "tick" sound. ABout 30% of the ticks caused
the control board to misfire, often sending the deck into stop, rewind,
fast-forward, or one or more all at the same time. I don't think you
want this to happen with things like gas valves!