On Fri, Apr 10, 2020 at 7:49 PM Daniel Sheen <danielsheen5@...> wrote:
Hi all,
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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.
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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).
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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).
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If anyone has any thoughts or has run into this before, suggestions would be appreciated.
