Defective Power supply in HP8711a Network Analyser.

If there is no schematic available that usually means it has a SMPS HP bought from someone else. Try the usual. Check for bad electrolytic capacitors. Test them for ESR and replace nay that are out of spec.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Hi Ivo, There are two leds close to the power connector of the PSU, on the back of the instrument. They are the PSU HW diagnostic for the PSU. How they behave when you turn on and off the power switch?

Unluckily it seems HP lost the schematics for the 8711A. I have one too, bought used on ebay. It had a bad smell from the fan every time I turned it on, so I changed all the ultra-low ESR capacitors on the PSU and now it is all right.

Anyways, I met on this group Caesar Valenti who was one of the HP8711A engineer team. He said me that the HP8711B is not so different from the HP8711A one (just the CPU board has changed, I guess). He told me that they have that schematics for the B series, but they are very huge and it's impossible to him to scan them all, but on request he can send just few sheets of the diagram for the part you need. You should try to contact him or just doing what Michael suggested you befor (and I did on mine).

When you repair it, if you want to play with it, I can give you the instruction on how to change it into an HP8712A VNA for free.

Have a great day.

Massimo

Does this can help?

73's pf

"Rivendel_Ivo" a écrit dans le message de news: snipped-for-privacy@n36g2000hse.googlegroups.com...

Dear Massimo.

Thanks for the response; also Micheal's idea was a good thing to do. So yesterday evening I checked all the DC capacitors in the +5, +12,

-15 and +15V circuits. At a first glance no optical defects were noticed, but when i removed the +5V caps they show a lot of wet electrolitic floating out at the bottom of the capacitor. Surely end of life behavior, so I exchanged these for new ones. And indeed, the supply was running !! After re-assembling the 8711 it worked as it always did. Hurray!!! BUT: the joy was not for long; after power off and reboot later on; the old error was back...... Out of the analyzer the power supply is working and booting OK; all voltages are there and clean. In the 8711 power-on does not work; green led is OK, red light is blinking. Must have something to do with the error signal LPwrFail, I guess. It seem that it cannot handle the load while booting. Now I will exchange all DC capacitors, including the two mains capacitors, so that will exclude a possible error there. In the mean time, I am very interested in a copy of the schematic of this SMPS unit in the HP8711. Could you possibly make a scan of the circuit behind this unit? Or how can I contact Caeasar Valenti for this? The best thing I can do is finding a second-hand schematic set on ebay or where....? At least thanks a lot for the help; much appreciated!!! Ivo.

Hi, despite its name, that manual is a maintenance manual. There never was a component level service manual for this series of analyser.

If the psu was running then I agree, change all the caps. I've repaired a few that way. If it wasn't running then I'd suggest you also check a few resistor values and the diodes too. I've had open diodes and open resitors in those supplies as well.

Don't forget, Massimo can show you how to convert that 8711 into an 8712, it's easy to do and it works. I also have a JEDEC file for the IBASIC PLD if that's wanted, I found that ibasic wouldnt work without it.

Greg

Hi Greg, so, do you have the jedec file for the IBASIC PLD? Since I use to have my own instruments FW back up, could you send me the file? Thank you. Have a great day Massimo

Ivo, I experienced a tantalum shorten on the CPU board, they were unusual non-polarized three terminals tantalum caps. I changed it following the suggestion of a friend of mine who repaired a lot of them having the the same problem of your.

Have a great day.

Massimo

Hello Massimo.

I will have a look. It is a strange thing though; normally, when you pull out the units one-by-one, you easily can find the one with shortened decoupling capacitors. With this error i can pullout any unit I like; still the SPMS stays in this non-boot hickup mode! I cannot figure out what is going out here.........that's why a schematic could help.... Greets; Ivo Maatman

Uhmm, Cesar Valenti is the nickname of the Agilent employee who is in this group. You should search for him here and you can ask him about the schematic. The only problem (I repeat myself), is that he can't scan all the schematic pages, you should at least identify the block where the problem is.

I imagine you checked the monitor board too, do you?

One more suggestion, some switching PSUs have the shortcircuit protection with a very long time retention function (when you remove the power supply too), do you turn off the instrument for 4/5 minutes after any test?

Have a nice day, good luck with your issue.

Massimo

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:

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.

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.

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:

Hi Caesar, nice to meet you again here, hope you are good. The wheather here is still very cold, and the flu is just around the corner. In Santa Rosa it should be better I guess, you are very lucky to live in Californian climate.

Ivo is very worried about his 8711, so I suggested him to ask you about it.

Ivo. I'm not sure where I found out it, but somewhere (this is for sure), there is a service note about the 8711 that explain some mods made to the PSU, one was about a power resistor (about one watt, I guess) added on the solder side near the backplane connector socket. Even if i remember well, it was added to avoid the PSU lockup when the 8711 power switch was left on and the power was switched outside the instrument. Does your 8711 PSU have that resistor soldered on the solder side?

Massimo

Hello Massimo.

No modifications on my 8711; the instrument is in a "virgin" state..... Very curious about the modifications, of course! I cannot find anything on the web though.

Weather state over here is typical Dutch March weather; cloudy with rain; strong winds 5 BF here near the German border and 9 degrees C over daytime... (PS: I was on my bike towards my work this morning....)

Were do you live?

Ivo.

Ok Ivo, I don't remember where I found the mods, I'm sure on the web. Now I go home, and I search for them in my home workshop. I should had printed them on paper and put them somewhere (my workshop is not what you can say "a well-kept environment").

I live in a small town few km from the Malpensa International Airport of Milan. Here is very cold and rainy today. I hope the spring came soon.

Massimo

Hi Ivo, I was wrong. The mods was to avoid the intermittent memory loss on the HP8711A with SN from 0000A00000 to 3325A00941. If your instrument has the SN between the above limits you should have one 680ohms / 3Watts resistor soldered under the PSU. The resistor must be connected to pin 9 and pin 16 of the PSU connector J5.

Hope this can help you, even if it seems to be another issue.

Have a nice day.

Massimo

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.