Last night I got the 7 or 8th 'list confirmation' mail. I truly wonder why, as my providers is absolutely not known for sending spam. Are there any other folks having this problem? It is getting a little anoying now. Ed -- Dit is een HTML vrije email / This is an HTML free email. Zeg NEE tegen de 'slimme' meter.

On Mon, Sep 15, 2014 at 11:38 PM, Alex van Denzel <alex.van.denzel at gmail.com> wrote: Thanks Alex, I wasn't aware of that link. I probably should have said that I have that manual in hardcopy, and am looking for a more detailed schematic. I've taken a closer look, and drawn the primary side of the power supply. It looks a lot like this one: http://www.repairfaq.org/sam/mon1ps.gif, except that it uses a 555 to provide a 100KHz clock, and a few minor details. The basics are the same. What I find is that the UC3842 isn't getting the juice it needs. Monitoring pin 7 (Vcc) shows that when I switch the supply on, Vcc ramps up to 14V, then drops down to 0.8V and stays there. When I switch the power supply off again, after a while Vcc ramps up to 14V again, then slowly ramps down to 0V. Any ideas as to what would cause this are welcome. Camiel.

On Tue, Sep 16, 2014 at 1:10 PM, Peter Coghlan <cctech at beyondthepale.ie> wrote: My 3842 seems to be dead differently ;-) If I power the 3842, it doesn't draw any power at all (at least not that I can notice). It also does not output the 5V reference voltage. That's all I could measure today, as I'm leaving home for a few days now. However, looking at the schematic I drew (http://www.vaxbarn.com/downloads/h7072_part_1.pdf), I think what happens next is that the 555, which is powered from the reference voltage, doesn't oscillate, and the 3842 causes the MOSFET to turn on continuously (again, I haven't verified this by measurement yet). There's a transistor between Vcc and ground that has its basis connected to the source of the MOSFET through a resistor. My guess is that the high current through the MOSFET causes this transistor to turn on, and bleed off the Vcc to ground. It also explains why the voltage comes back - briefly - when I switch the power supply off. As the capacitors on the 300V line lose their charge, the voltage across the MOSFET drops, causing the current through it to drop as well, and at some point it's low enough to turn the transistor back off, after which the capacitor on Vcc starts charging again. Plausible? At any rate, I have ordered a few new 3842's, so I'll continue my experiments when I get back on saturday. Thanks, Camiel