Re: Defective Power supply in HP8711a Network Analyser.

Hi Massimo;

i found another thread from Caesar and made him following mail: (I
hope he will respond).

Hello Caesar.

I have serious problems with my dearest HP8711a analyzer; already
tried a lot, but the problem now is missing schematics around the
power supply unit. See threat:
http://groups.google.com/group/sci.electronics.equipment/browse_thread/thread/83a4ee0eadaf7730?hl=en
Problem is that the analyzer sometimes will boot as nothing seems to
be wrong, but suddenly shuts down, or mostly the analyzer will not
boot at all; the SPMS unit red light blinking; sort of
current_limiting hick-up mode.
Most discussions with Massimo are indicating defective capacitors
anywhere in the analyzer; I already had a defective CAP on the CPU
board some years ago; and replacing this one (+5V) was very effective.
While inspecting the electrolithic caps in the SMPS I noticed a lot of
them leaking electrolithic.
So I exchanged ALL 22 caps within the SMPS with high temp, long life
and higher voltage rated caps.......no effect.
So I Changed ALL CAPS and tantalium ones (more than 20 pieces) on the
CPU board..............no effect.........

Currently I am running tests with only the SMPS and the CPU board
running; also the monitor supply cable from the CPU board towards the
monitor unit is not connected.
Still the analyzer will not boot and stays in this hickup mode; FAN
silent and no power_up; CPU board status LED only indicating blinking
number 8 (only initial power, no software boot possible.)
Sometimes at power-on there is a boot as-normal.....strange... I also
have the idea that it takes the SMPS an enormous time to recover from
an error....when i try it an hour later, mostly there is a boot
possible.......Logically I cannot explain this...current limit or no
current limit....but no reset time normally with this sort of SMPS
units.

I would like to know which one of the voltages is causing the problem:
+5, +12, +15 or -15 Volts...
Therefore I need the schematics of the SMPS.
As I understood you are the proud owner of a schematic set....
Would you be so kind to make me a copy with a scanner of the SMPS
schematic set?
I am using this analyzer at home in my "lab" here in Borne in the
Netherlands, together with a HP8594E and a HP8559A spectrum analyzers
an I cannot live without a working 8711...........

Thanks in advance;
Ivo Maatman.
.

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