X4046 weird problem.

bubzy · Posted: Thu Jul 26, 2012 1:56 am Post subject: X4046 weird problem.

Hey,
Ive been using 2 4046's for a while with no problems, the other day after deciding that the sine wave wasnt *quite* round enough, i unplugged all the power connections from one oscillator, and when i plugged it back in its not working.

the 4046 chip gets VERY hot, have tried more than one chip in this position, the tl074 also warms up but not as much,
there doesnt seem to be any shorting with power, as i can simultaneously plug the other oscillator in and it runs no problem.

the other weird thing that happens is that when I power down the circuit, i get a 3 or 4 second delay and then an oscillaton from very high going down to very low as the capacitors in my psu run out of power.

any suggestions? (ive replaced all the chips and resoldered a few iffy looking resistors)

many thanks

elmegil · Posted: Thu Jul 26, 2012 5:34 am Post subject:

Probably not much of a suggestion, but...that sounds like it's running, just at a ridiculously high frequency. When you cut power, the frequency drops off.

1) do you have a scope to look at the output (I suspect you do from other conversations...) and confirm that nothing is coming out, or high frequency is coming out?

2) what is static sensitive in the frequency control section? Anything there that if it was shorted could cause the frequency range to jump ridiculously?

I'm not very experienced with expo converters, but looking at my X4046 schematic, I'd be looking at IC2 ofr whatever you're using for the Q1/Q2 pair. (edit: duh, should read it all...you replaced all the chips, so I'd be looking at the transistors then) I suppose it's also possible for the hard sync to be misbehaving, but it seems less likely.

Disclaimer: I have not been doing this a long time, so I reserve the right to be completely off in the weeds Very Happy

bubzy · Posted: Thu Jul 26, 2012 6:35 am Post subject:

i get a sort of ac looking wave when i plug scope into it, doesnt change at all.

funny you shuold mention hard sync as i was messing about with that on it a couple of days ago.
where shuold i be looking if thats the trouble?

fonik · Posted: Thu Jul 26, 2012 12:30 pm Post subject: Re: X4046 weird problem.

bubzy · Posted: Thu Jul 26, 2012 12:33 pm Post subject:

pretty sure i didnt do anything.
its unlikelytheres a solder bridge, however, with me, anything is possible. im going to have another look in a bit to make sure that i havent missed anything important. (i even moved the HF and scale pots :/) time to recalibrate.

will post results back later

elmegil · Posted: Thu Jul 26, 2012 8:29 pm Post subject:

What's the frequency of your wave?

the only thing that seems likely to be a problem for the Hard Sync (as far as handling causing it to zort) would be Q3, NPN transistor. I'd see if I could measure the current going in on pin 11 of the 4046 and verify all its voltages too.

I'd also back up; when your'e adjusting the coarse/fine pots, do you see voltage differences at pin 2 of IC2? What about at the base of Q1? What's voltage at the collector of Q1 (connected directly to pin 6 of IC2)? It ought to be held to ground by the op amp if I have it right....as before with my disclaimers, I can't say I'm terribly confident about expo converters' behavior...

I haven't re-read the build notes/troubleshooting notes at Scott's site, but I'd think there might be some clues there too.

bubzy · Posted: Thu Jul 26, 2012 10:59 pm Post subject:

seems i didnt change ic2 Very Happy

now working. thanks for your efforts

fonik · Posted: Fri Jul 27, 2012 2:46 am Post subject:

elmegil · Posted: Fri Jul 27, 2012 5:37 am Post subject:

Cool, glad it's working Smile