Defective Power supply in HP8711a Network Analyser.

[Caesar Valenti]

Rivendel_Ivo wrote:

On Mar 11, 9:44 am, Max65 <mpor...@tele2.it> wrote:

In the mean time, just got schematics from Ceasar by mail!!
I will try to find the ghost in the SMPS box....I will let you
know!

Great!
Ceasar is a great guy.

Let me know,
when you fix it, I can give you the mods to convert it to a full
loaded 8712 for free.
(If you want I can give you now, but it's better you fix it before).

Massimo


With the schematics by hand, it was not very difficult to pinpoint the
problem.
The SMPS of the 8711 is equipped with Under and Over-voltage lockout
circuitry; this is situated on a sub-PCB in the supply itself. This
OVL and UVL circuits are based on a common LM139 comparitor; this one
shows extreme bias on the inputs so treshold levels are wrong.
The simplest thing to do (IC exchange was difficult to realize) was a
complete disabling of the UVL and OVL circuit.
The supply works well and the analyzer is operational!
Thanks for the help !!!
Ivo.

Glad you got it working.....it's nice to know that the schematics helped.

CV

 

[Don Bowey]

"Rivendel_Ivo" <rivendel@home.nl> wrote in message news:59cc83f3-7ef3-4c96-b316-b545acfb5e03@59g2000hsb.googlegroups.com...

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.

No problem Moron, now get out of here.

 

[Don Bowey]

"Caesar Valenti" <caesarv@email.com> wrote in message news:47d42584$0$36374$742ec2ed@news.sonic.net...

Sorry guys, I have not checked this newsgroup for several months...shame
on me!

The 8711 family used a 3rd party power supply and CRT. While I do have
schematics for most of the "Agilent" parts, I don't think any schematic
exists for either of these parts....or at least I have not found any.
If I remember, I will ask around tomorrow....but don't get your hopes
up. Most of the people that would have had a schematic are long gone.

Our service department will be moving to a remodeled building on our
Santa Rosa site in June and there will be no room for much of our spare
obsolete equipment. If I find any junked 871x power supplies I will try
to salvage them (which, btw, is against policy.)

We are preparing for the move by throwing out many, many manuals that
would be useful to hobbyists. However we are trying to keep anything
that is not already digitized and on the web. There is no profit in
supporting hobbyist, so management will not support me, however I will
try to do a best-effort support if it is not too time-consuming.

If you need to contact me; use caesarv-at-email.com. This is not my
real name. This is my "junk" email address, but I do check it every
couple of days.

CV




Rivendel_Ivo wrote:
Hello Massimo.

Going back to basics it proved that the SMPS of the HP8711a hates it
to be plugged into the cabinet, even only connected to the backplane;
result: hickup mode. (so no 8711 units in the 8711 rack at all!!)
In the open the SMPS works fine (all voltages unloaded), but I found
out that the -15 Volt GND return hates it to be connected to GND of
the cabinet (this connection is on the backplane of the 8711) or to
GNDs of the other voltages.
All voltages are fine, no DC shorts between anything, and I can GND
all voltages, except the -15V. By grounding only a few mA will float
though, but this brings the SMPS in the hick-up mode, like it does in
the 8711.

Could no-load situation bring this? Or is something wrong with the
current sense system, so the SMPS does not boot?

Do you have any idea?

Ivo.

Hey Stop TOP POSTING idiot.