I recently ordered my first batch of pt2399's. I've read countless post about these chips locking up. At first I thought this was my prob but I'm not thinking it is. I'm using the vero layout at sabrotone.com. The circuit works perfect sometimes and then all I get is the bypass. There's a 47uF cap to grd off of pin 2 that I think might have somthing to do w the prob. I can stick my screwdriver down and arc the leads and it triggers the circuit back on. Some times I have to arc the out and ground pins of the 7805. Any tips. I'm 95% sure the circuit work is good this is my first build w the chip so I'm still inexperienced w it.
First thing I'd do is replace that cap. It's necessary, so it sounds like it isn't making connection to ground somehow.
Jacob
that's what I thought. I replaced it once. You think I should give it a go? If you look at the lay out, I had the ground wire on the row below the 9v row. When I wired it up I had the 9v wire to ground, then the one below it to 9v. I'm guessing I damaged somthing doing that and replaced every cap. This Is the prob that trmains.
That cap is the filtering for the internal reference voltage. So I'm not really sure what it means that shorting VREF to ground is making the circuit work. ???
What do you have the delay time set to? If the PT2399 is fired up with the resistance off pin 6 too low, it will lock up and stop working until you power it up again.
I'm not sure either. To behonest I just copied the vero hoping it would work. I had NO clue about this chip and still scratchin my head over it. I talk to merlin through email and he said "if that's what's happening clip the cap off and see what happens". LOW and BEHOLD it's alive live ve ve... It's works fine now.. Should I try putting a smaller cap in there? It damn sure is working now.
hmm.. I don't quite understand why you'd clip the cap at pin 2 but here is what I've found:
Some of the chips lock up when the digital GND (pin 4) is not directly connected to ground. When connecting the digital ground to the delay pot loop some pt2399's lock up. Not all of them do it. But I've had about 10 out 20 do it.
From reading the schem take the 1k in the delay pot loop and connect it to ground and then take pin 4 of the pt2399 and connect it to ground.
Technically according to the datasheet the AGND and DGND are internally connected with a resistor but I make the connections to ground on all my layouts now and I haven't had one lock up yet.
Josh