In article , sck0006 wrote:

I have an 8640b with issues. As frequency is increased in each range,
it falls off to nothing or very low at the high end. Low end seems to
work ok. I aligned the two seperate detents on the range selector
switch, but still the same problem. Is this a common failure, or am I
going to have to dig deeper?

Steve-

The only common problem I've heard of, is cracked or broken nylon gears in
the tuning mechanism. I've never had mine apart, so can't tell you what
to look for.

I imagine that there could be additional circuits that must be tuned to
track frequency. If a gear was broken, it would mess up the tracking and
could explain low output at one end of the range.

The person who told me about this indicated that he had custom metal gears
made for one(s) he repaired. They may not be commonly available.

Fred