Hi Jorgen,
Many thanks for the reply.
Fortunately it turned out to be the input capacitor and not the diodes.
It took several days to find an allen key small enough to get the probe apart.
It appeared the diodes had already been changed.
The small 470 pF input capacitor looked ok but the lead going to the tip was open circuit just inside the epoxy case. When I un-soldered the component the lead fell out.
Replacing the cap with a SMD component fixed all the problems.
Thanks for the comment about the Vector voltmeter. I was given one of those to repair at the same time. Apparently one of the channels doesn't work.
I will have a go at that one next week.
Once again many thanks for the reply and I will file the information for future use.
David
At 06:23 AM 17/09/2004, you wrote:
--- In hp_agilent_equipment@..., David Hopkins
<davhop@b...> wrote:
Gentlemen,
Hi David,
mostly the Sampling Gate Diodes fail, and in very seldom cases
the following Fet, but normally the diodes protects the Fet
due to "fuse acting" before the Fet blows out.
You can substitute the Sampler Diodes with HP5082-2815
matched quad shottky diodes.
Self matching from fast shottkys is difficult but possible,
but they are matchet not only in forewardvoltage, as i remember right
also in capacitance as this affects the bridge balance, too.
The original Diodes have a Special HP-Number which is never found
again in any other document :-(, but the (now obselete, but here and
there still available, if in doubt, ask,i have some,) -2815 Quad works
well.
The HP 8405 Vector Voltmeter has the same Sampling Bridge and there
it also works well.
I have never understood why the probes are not field repairable-...
Hope that helps,
Jorgen
dj0ud
I have a HP 3406A Broadband Sampling Voltmeter I am repairing.
According to the test procedure in the manual , the probe assembly is
faulty and should be replaced as it is not field repairable.
I doubt if these are available from HP and if they were one could not
afford the price they would ask.
Does anyone have any experience with fixing these probes?
Failing this is there anyplace a replacement can be found.
Thanks
David
David Hopkins (VK4ZF)
Queensland
AUSTRALIA
davhop@b...
S 27, 22.294 E153, 11.008
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David Hopkins (VK4ZF)
Queensland
AUSTRALIA
davhop@...
S 27, 22.294 E153, 11.008
