There are several HP 8556s on E-bay
Cheers!
Bruce
Quoting Steve Dench <sjdench48@...>:
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Hi Bernie
I have only been able to estimate the 90Hz signal by injecting a signal
into the input from a sig gen at a high amplitude to override the spurious
signal and see where it sits on the waveform. I actually suspect that the
spurious signal is nothing like 90Hz but a signal close to the LO signal or
a harmonic of it.
Regarding the mixer, I have replaced the IC and the balance trim pot to no
effect.
I totally agree that the best way to fix it may be another 3850. I have for
some time been on the lookout for a HP8556 plug in for my HP141T that would
solve all the problems.
Thank you for your suggestions
Steve Dench
On Thu, 8 Oct 2020, 11:07 am Ham Radio, <bernard.murphy@...> wrote:
Is the spur exactly 90 HZ? That might be a clue.
I would double check the mixer trim pot connections with an ohm meter on
low range and also reflow the solder of joints.
You might need another 3580 to find the spur. :-(
--
Regards, Bernie Murphy
