On Sat, 24 Apr 2010 07:51:13 -0700, "Chris F."
wrote:

I'll stand on my comments that your clip lead and external power
supply kludge is probably causing problems. Find some suitable
electrolytics and place them across where the battery would normally
connect. The idea is to reduce the impedance that the counter sees in
the direction of the power supplies. That should reduce the
motorboating (oscillation).

I tried putting a 100uF cap in that area, the result was that it greatly
increased the frequency of the stray clicks....

Did you figure out where the yellow electrolytic in the photo was
connected? Power supply filter or meter integrator?

Find an oscilloscope that can tolerate some high voltage (i.e. 100x
probe). Look at the power supply line. Got pulses? If so, get rid
of them with a filter cap.

Old carbon composition resistors tend to change value with age (and
moisture). With the power off, you might walk though the pile and see
if there are any that are radically off value. I don't think this is
causing the problem, but it might be contributory.

I wonder if a row of 10 9-volt batteries would work?

Probably, but rather expensive. It should work with your external
power supplies, but due to the apparent lack of power supply
filtering, it might be oscillating.

If all else fails, trace out the schematic. It doesn't look all that
messy and you can probably use the DG-9 schematic as a guide. The
author of the web site where we found the DG-9 schematic is the
founders son. Send him email asking if he has a DG-7 schematic or if
he knowns anyone that can help.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558