On 4/10/20 1:48 PM, Daniel Sheen wrote:
I have a rather bizarre problem with a 5343A counter. Observed symptoms
are that the high frequency input works reliably up to about 250MHz,
reads garbage from around 250MHz-800MHz, and then seems to work fine
from 800MHz upward through 1GHz (I only have an 8640B handy atm so can't
really test higher than that). Cranking up the input power a bunch seems
to reduce the dead band to closer to 400MHz-600MHz.
The counter initially failed troubleshooting step 4 in the service
manual. That was resolved by replacing the A10 board (from another
counter with a blown sampler). It now passes step 5 and is marginal on
step 6 (sensitivity is a little lower than it ought to be but it seems
to work).
The one other observation I've made is the IF amplitude into and out of
A11 drops off rapidly if an input is tuned into the range of frequencies
that it's insensitive to, but I'm struggling to find a plausible
explanation for why that could occur given my understanding of the
counter design (that wouldn't also make higher frequencies not be detected).
If anyone has any thoughts or has run into this before, suggestions
would be appreciated.
That almost sounds like the "suck-outs" that are typical of a damaged
or loose hardline cable. I would check the input connectors and, if
there's the standard SMA-terminated 0.141" hardline on the inside, look
for hairline cracks around the solder joints around the connectors, or
similar damage.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
Dave McGuire