On 24 Aug 2014, at 4:30 pm, Josh Dersch <derschjo at gmail.com> wrote:
Thanks! Lifting CR22 (which took awhile to find, it's actually clear on the other
side of the PCB from the rest of the supply) made no difference in behavior.
Removing IC 63 (which is a 7805, nice guess) and reading voltages on the positive lead of
C67 yields about 15VDC. The resistance between the +5V lead of the IC63 socket and ground
is about 3.5K ohms, so it doesn't look like there's a dead short here. Would the
7805 be a likely suspect here? Any easy way to test it?
Thanks,
Josh
The 3 pins on the 7805 are: DC input / Common (ground) / +5V DC regulated output.
All you really need to test it is apply a voltage anywhere from 7.5 to 25V DC between the
input and the common, then apply a small load (and measure the voltage) across common and
the output (should be close to 5V. In a real life circuit you would have capacitors on
both the input and output to filter any ripple, but shouldn?t be required for a simple
test.
In the Interact circuit there are 4 capacitors on the output of the 7805, one of them
could be the problem if the 7805 checks out ok.
I would be inclined to put in a new 7805 anyway (since you already have it out), but I
have a heap of them lying around..
Chris