On 16/09/2014 11:30, Camiel Vanderhoeven wrote:
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.
I have exactly the same problem with a DECstation 5000. For this PSU the
UC3842 and 555 are mounted on a separate daughter board. I removed this
board and powered it from a bench supply and it seemed to work just
fine. The problem must be on the main board somewhere but unfortunately
I haven't found it yet.
Matt