Re: HP-8753E Power Cycles at Start Up
Late to the party but just in case it helps someone:
My 8753C which uses the same PSU had a cycling fault. It was caused by shorted diodes on the A15 Pre-reg board. CR6 and CR7.
Cheers, Roger
On Mon, 29 Aug 2022 at 14:22, Ozan < ozan_g@...> wrote: On Sun, Aug 28, 2022 at 06:12 PM, peter bunge wrote:
Can someone tell me how the control loop in the pre-regulator controls the 5vD supply? What I see is T1 connected to line at E1 and E2 and switching FETs that don't seem to control anything and only drive RT1 and RT2.Is there a winding in the loop that acts like a MagAmp? The common connection of the?FETs connects through capacitor?C8 to A15A1 transformer,?what and where is that? .
What am I missing? The manual is very vague simply stating "The?+5D supply is regulated by the control loop in A15"
Am I missing a schematic? I have one for 08753-60215 and one for 08753-60115. there is a T1 on each board which makes it more confusing.
-----
Hi Peter,
I briefly looked at the schematic of 8753A.
Hopefully 8753E is similar. Mains input is rectified on C3 and C4, RT1 and RT2 are inrush current limiting NTCs. Q1 and Q2 turn on alternatively, creating an AC waveform that flows through C6 (probably C8 in your schematic) and primary of "Power Transformer". Return path of the primary is through "T3 Over Current Detection" transformer and back to mains input through S2 switch (which selects 110/220 tap points). 8753A schematic and board layout show the power transformer on A15 board.?
Ozan
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Re: HP-8753E Power Cycles at Start Up
On Sun, Aug 28, 2022 at 06:12 PM, peter bunge wrote:
Can someone tell me how the control loop in the pre-regulator controls the 5vD supply? What I see is T1 connected to line at E1 and E2 and switching FETs that don't seem to control anything and only drive RT1 and RT2.Is there a winding in the loop that acts like a MagAmp? The common connection of the?FETs connects through capacitor?C8 to A15A1 transformer,?what and where is that? .
What am I missing? The manual is very vague simply stating "The?+5D supply is regulated by the control loop in A15"
Am I missing a schematic? I have one for 08753-60215 and one for 08753-60115. there is a T1 on each board which makes it more confusing.
----- Hi Peter, I briefly looked at the schematic of 8753A. Hopefully 8753E is similar. Mains input is rectified on C3 and C4, RT1 and RT2 are inrush current limiting NTCs. Q1 and Q2 turn on alternatively, creating an AC waveform that flows through C6 (probably C8 in your schematic) and primary of "Power Transformer". Return path of the primary is through "T3 Over Current Detection" transformer and back to mains input through S2 switch (which selects 110/220 tap points). 8753A schematic and board layout show the power transformer on A15 board.? Ozan
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Re: HP-8753E Power Cycles at Start Up
Thanks Bruce. I have seen that problem on another 8753 and the fans are very specific. The symptoms here are different but I will investigate that as well.? Peter.
On Sun, Aug 28, 2022 at 8:40 PM Bruce Lane < kyrrin@...> wrote: ???? I'm coming in late to the discussion, but...
???? My first VNA had a similar problem. The issue turned out to be a
defective case fan. You see, the power supply had a circuit in it to
detect pulses from the fan's tachometer. No fan movement = no pulses =
no full power-on.
???? Just thinking out loud.... Happy tweaking.
On 28-Aug-22 16:53, peter bunge wrote:
> Not so easy to recap. Do you have a list of suitable replacements from
> DigiKey or Mouser?
> How do you get the boards out? Do I have to unsolder anything? Is the
> power switch mounted?to the PCB?
> I have the PreReg supply split open.
> I also do not think this is the problem because the manual
> troubleshooting points to the +5v supply which is where my
> troubleshooting pointed?from a different?direction. If the?caps are
> easy to get at with the boards out I can check them for value and
> resistance. I prefer to identify a?definite fault rather than randomly
> replace components.
> I put the?8753B on a?variac and dropped?the?voltage to 100VAC but
> could?not?trigger the fault. This probably eliminates the rear half of
> the PreReg with the two big capacitors,?but not the front board with
> the six big?caps.
> It worked fine for?a?few hours but the next time I turned it on
> the?fault returned. I took?the?Pr-Regulator out and split the?module
> and turned it on and it?is back to working perfectly. I wiggled
> all?connectors?and cannot?get?it to quit again. I don't think it is a
> bad connection.
> I checked the current in all wires to the display when the fault was
> happening and there was nothing obvious (disconnecting the display
> cured the fault repeatedly but it was only because it dropped the
> drain on the +5v. It is an LCD display).
> It seems more like a marginal?trip point setting which is why I have
> the supply open.
>
>
> On Sun, Aug 28, 2022 at 4:42 PM tony sayer <tony@...> wrote:
>
>? ? ?In message <[email protected]>, Burt K6OQK
>? ? ?<biwa@...> writes
>? ? ?>? ? Rich,
>? ? ?>
>? ? ?>? ? I have cured a lot of weird problems by fixing the obvious
>? ? ?things
>? ? ?>? ? first.? I suspect that if you were to re-cap the power supply
>? ? ?>? ? module you would be pleased.? That's been my experience in
>? ? ?90% of
>? ? ?>? ? the symptoms you describe.
>
>? ? ?FWIW - Mine too!...
>
>? ? ?>
>? ? ?>? ? Burt, K6OQK
>? ? ?>
>
>? ? ?--
>? ? ?Tony Sayer
>
>? ? ?Bancom Communications? ?U.K.
>
>
>
>
>
>
>
>
>
>
--
Bruce Lane, ARS KC7GR
kyrrin@...
"Quando Omni Flunkus Moritati" (Red Green)
|
Re: HP-8753E Power Cycles at Start Up
Can someone tell me how the control loop in the pre-regulator controls the 5vD supply? What I see is T1 connected to line at E1 and E2 and switching FETs that don't seem to control anything and only drive RT1 and RT2.Is there a winding in the loop that acts like a MagAmp? The common connection of the?FETs connects through capacitor?C8 to A15A1 transformer,?what and where is that? . What am I missing? The manual is very vague simply stating "The?+5D supply is regulated by the control loop in A15" Am I missing a schematic? I have one for 08753-60215 and one for 08753-60115. there is a T1 on each board which makes it more confusing.
Not so easy to recap. Do you have a list of suitable replacements from DigiKey or Mouser? How do you get the boards out? Do I have to unsolder anything? Is the power switch mounted?to the PCB? I have the PreReg supply split open. I also do not think this is the problem because the manual troubleshooting points to the +5v supply which is where my troubleshooting pointed?from a different?direction. If the?caps are easy to get at with the boards out I can check them for value and resistance. I prefer to identify a?definite fault rather than randomly replace components.? I put the?8753B on a?variac and dropped?the?voltage to 100VAC but could?not?trigger the fault. This probably eliminates the rear half of the PreReg with the two big capacitors,?but not the front board with the six big?caps.? It worked fine for?a?few hours but the next time I turned it on the?fault returned. I took?the?Pr-Regulator out and split the?module and turned it on and it?is back to working perfectly. I wiggled all?connectors?and cannot?get?it to quit again. I don't think it is a bad connection. I checked the current in all wires to the display when the fault was happening and there was nothing obvious (disconnecting the display cured the fault repeatedly but it was only because it dropped the drain on the +5v. It is an LCD display). It seems more like a marginal?trip point setting which is why I have the supply open.?
On Sun, Aug 28, 2022 at 4:42 PM tony sayer < tony@...> wrote: In message <[email protected]>, Burt K6OQK
<biwa@...> writes
>? ? Rich,
>
>? ? I have cured a lot of weird problems by fixing the obvious things
>? ? first.? I suspect that if you were to re-cap the power supply
>? ? module you would be pleased.? That's been my experience in 90% of
>? ? the symptoms you describe.
FWIW - Mine too!...
>
>? ? Burt, K6OQK
>? ?
--
Tony Sayer
Bancom Communications? ?U.K.
|
Re: HP-8753E Power Cycles at Start Up
I'm coming in late to the discussion, but...
??? My first VNA had a similar problem. The issue turned out to be a defective case fan. You see, the power supply had a circuit in it to detect pulses from the fan's tachometer. No fan movement = no pulses = no full power-on.
??? Just thinking out loud.... Happy tweaking.
toggle quoted message
Show quoted text
On 28-Aug-22 16:53, peter bunge wrote: Not so easy to recap. Do you have a list of suitable replacements from DigiKey or Mouser?
How do you get the boards out? Do I have to unsolder anything? Is the power switch mounted?to the PCB?
I have the PreReg supply split open.
I also do not think this is the problem because the manual troubleshooting points to the +5v supply which is where my troubleshooting pointed?from a different?direction. If the?caps are easy to get at with the boards out I can check them for value and resistance. I prefer to identify a?definite fault rather than randomly replace components.
I put the?8753B on a?variac and dropped?the?voltage to 100VAC but could?not?trigger the fault. This probably eliminates the rear half of the PreReg with the two big capacitors,?but not the front board with the six big?caps.
It worked fine for?a?few hours but the next time I turned it on the?fault returned. I took?the?Pr-Regulator out and split the?module and turned it on and it?is back to working perfectly. I wiggled all?connectors?and cannot?get?it to quit again. I don't think it is a bad connection.
I checked the current in all wires to the display when the fault was happening and there was nothing obvious (disconnecting the display cured the fault repeatedly but it was only because it dropped the drain on the +5v. It is an LCD display).
It seems more like a marginal?trip point setting which is why I have the supply open.
On Sun, Aug 28, 2022 at 4:42 PM tony sayer <tony@...> wrote:
In message <[email protected]>, Burt K6OQK
<biwa@...> writes
>? ? Rich,
>
>? ? I have cured a lot of weird problems by fixing the obvious
things
>? ? first.? I suspect that if you were to re-cap the power supply
>? ? module you would be pleased.? That's been my experience in
90% of
>? ? the symptoms you describe.
FWIW - Mine too!...
>
>? ? Burt, K6OQK
>
--
Tony Sayer
Bancom Communications? ?U.K.
--
Bruce Lane, ARS KC7GR
kyrrin@...
"Quando Omni Flunkus Moritati" (Red Green)
|
Re: HP-8753E Power Cycles at Start Up
Not so easy to recap. Do you have a list of suitable replacements from DigiKey or Mouser? How do you get the boards out? Do I have to unsolder anything? Is the power switch mounted?to the PCB? I have the PreReg supply split open. I also do not think this is the problem because the manual troubleshooting points to the +5v supply which is where my troubleshooting pointed?from a different?direction. If the?caps are easy to get at with the boards out I can check them for value and resistance. I prefer to identify a?definite fault rather than randomly replace components.? I put the?8753B on a?variac and dropped?the?voltage to 100VAC but could?not?trigger the fault. This probably eliminates the rear half of the PreReg with the two big capacitors,?but not the front board with the six big?caps.? It worked fine for?a?few hours but the next time I turned it on the?fault returned. I took?the?Pr-Regulator out and split the?module and turned it on and it?is back to working perfectly. I wiggled all?connectors?and cannot?get?it to quit again. I don't think it is a bad connection. I checked the current in all wires to the display when the fault was happening and there was nothing obvious (disconnecting the display cured the fault repeatedly but it was only because it dropped the drain on the +5v. It is an LCD display). It seems more like a marginal?trip point setting which is why I have the supply open.?
On Sun, Aug 28, 2022 at 4:42 PM tony sayer < tony@...> wrote: In message <[email protected]>, Burt K6OQK
<biwa@...> writes
>? ? Rich,
>
>? ? I have cured a lot of weird problems by fixing the obvious things
>? ? first.? I suspect that if you were to re-cap the power supply
>? ? module you would be pleased.? That's been my experience in 90% of
>? ? the symptoms you describe.
FWIW - Mine too!...
>
>? ? Burt, K6OQK
>? ?
--
Tony Sayer
Bancom Communications? ?U.K.
|
Picol,
It has been a while since I tried (with partial success) to repair on of these YTOs.? If I recall correctly, the output of the NPN oscillator is buffered by a FET amplifier with the drain fed from the +5v supply.? If that FET is a GaAs type, it probably requires a negative bias to turn off.? It might appear as a (near) short to ground with no negative bias available.
--John Gord
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Show quoted text
On Sun, Aug 28, 2022 at 11:18 AM, @Picol wrote:
Hello everyone,
about a year ago, turning on my HP8563E spectrum analyzer, several errors appeared, including the ravenous error 334.
From research on the net, and a direct inspection, I found that the YTO model 5086-7906 was broken.
Pin 1, corresponding to 4 of connector J3, of the 5 VDC power supply, appears to be shorted to ground.
About a month ago, I bought an HP8560E Spectrum Analyzer at a good price with the intention of using its YTO for my HP8563E.
In fact, the analyzer cost me as much as a used YTO!
Before mounting it, I checked that the voltages of +5V, +15V and -15V were present.
Then I mounted the YIG oscillator, checking several times that the connectors were mounted correctly. Which I always do when I reassemble an electronic instrument.
When I turned the spectrum analyzer back on, I found that the new YTO was also broken !! A check of the same confirmed this.
What could I have done wrong? Has anything like this ever happened to anyone? Is there anyone in the group who has experience with these damn YTOs?
Given that I'm not really fasting with electronic instruments, such a thing had never happened to me.
I contacted a local company that repairs the YTO at a price of around 800 euros but I'm afraid that if I don't find out the reason for the break, this too could break ...
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Re: HP-8753E Power Cycles at Start Up
In message < [email protected]>, Burt K6OQK <biwa@...> writes Rich,
I have cured a lot of weird problems by fixing the obvious things
first.? I suspect that if you were to re-cap the power supply
module you would be pleased.? That's been my experience in 90% of
the symptoms you describe. FWIW - Mine too!...
Burt, K6OQK
-- Tony Sayer Bancom Communications U.K.
|
Hello everyone,
about a year ago, turning on my HP8563E spectrum analyzer, several errors appeared, including the ravenous error 334.
From research on the net, and a direct inspection, I found that the YTO model 5086-7906 was broken.
Pin 1, corresponding to 4 of connector J3, of the 5 VDC power supply, appears to be shorted to ground.
About a month ago, I bought an HP8560E Spectrum Analyzer at a good price with the intention of using its YTO for my HP8563E.
In fact, the analyzer cost me as much as a used YTO!
Before mounting it, I checked that the voltages of +5V, +15V and -15V were present.
Then I mounted the YIG oscillator, checking several times that the connectors were mounted correctly. Which I always do when I reassemble an electronic instrument.
When I turned the spectrum analyzer back on, I found that the new YTO was also broken !! A check of the same confirmed this.
What could I have done wrong? Has anything like this ever happened to anyone? Is there anyone in the group who has experience with these damn YTOs?
Given that I'm not really fasting with electronic instruments, such a thing had never happened to me.
I contacted a local company that repairs the YTO at a price of around 800 euros but I'm afraid that if I don't find out the reason for the break, this too could break ...
|
Re: Hp 8590a spectrum analyzer
Very interesting videos. I scoped the dc power rails and a couple have heavy noise . I don't think it would hurt to recap the swps. I may start there and see if it clears anything up , besides if it doesn't need it now it will soon. I'm wondering if the shotky diodes should be swapped out also on the 1st converter given its age. . I can still get them on ebay.?
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Re: PNA Cal Kit Editor software
Is this what you're after:
Cal Kit EditorThis Cal Kit editor can be installed on a PC and used to enter or import cal kits without the need for a PNA. Once entered or modified, the kits can then be transferred to the PNA. In addition to being able to import 8510/8753/872x Cal kits with little or no modification needed, this new version also supports the new '.xkt' XML cal kit file format which FieldFox analyzers have begun using and PNA will soon. It uses an interface similar to that used in the PNA, so the learning curve is minimal. Please note that '.ckt' files saved by this new version of this editor will only function for PNAs with Firmware A.07.50 and above. It includes data-based standards capabilities. Refer also to the PNA Help file for instructions.
?this 19 MB msi file. Rev: 1.0.5045.0 (Oct 2013)
?this 2 MB version for 4.83 to 4.87.01 firmware?only!?Rev: A.04.83 (Mar 14 2005)
From?
TonyG
Yes, thank you. I will have to get into the habit of looking there, as it archives most sites. I only know of one website
that was at one time blocking the IP address of the Wayback Machine - for example
which was annoying when I wanted to find out the specification of something I had bought. Maybe
the Wayback Machine is using different IP addresses, or maybe Justin has decided to not block it any longer.
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Re: HP 8901B/8902A History
the 8902A is essentially an enhanced 8901B ....the enhancement being the low level power measurements when used with the 11722A? ( and others )?
They run the same firmware and most of the parts are the same ...about 90%
|
Re: PNA Cal Kit Editor software
Is this what you're after:
Cal Kit EditorThis Cal Kit editor can be installed on a PC and used to enter or import cal kits without the need for a PNA. Once entered or modified, the kits can then be transferred to the PNA. In addition to being able to import 8510/8753/872x Cal kits with little or no modification needed, this new version also supports the new '.xkt' XML cal kit file format which FieldFox analyzers have begun using and PNA will soon. It uses an interface similar to that used in the PNA, so the learning curve is minimal. Please note that '.ckt' files saved by this new version of this editor will only function for PNAs with Firmware A.07.50 and above. It includes data-based standards capabilities. Refer also to the PNA Help file for instructions.
?this 19 MB msi file. Rev: 1.0.5045.0 (Oct 2013)
?this 2 MB version for 4.83 to 4.87.01 firmware?only!?Rev: A.04.83 (Mar 14 2005)
From? TonyG
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Re: "ADDITIONAL STANDARDS ARE NEEDED" when using E-Cal
Forgot to mention there are 2 tables of through data, table 3 which is used during calibration (all PIN's disabled #0000), and table 4 which is used for performance verification (#0200 - 2 PIN's enabled).
This means that the verification measurement has little in common to the calibration process.?? The same 2 PIN's are used during calibration but if anything was wrong with those it will show up as a discrepancy in S11/S12 or S22/S21
--
Wayne
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Re: "ADDITIONAL STANDARDS ARE NEEDED" when using E-Cal
Bruce, Steffan,
I think you are forgetting that there is another verification you can perform - completely remove the ECal module and connect the test ports together and verify the error in the calibration is close to 0.00dB across the frequency range.? That is your error ;-)? ? You can also confirm the phase starts at on the right side of the smith chart for the open port as one would even in manual calibration.
Answering your question the signalling on the DB25 uses the same protocol, in fact the first board is the same between the low and high band modules.? The primary difference is the low band uses 7 switch signals to the lower board and the high band module uses a total of 16.
Analog voltages to the PIN switches are different with the low band using 0 and -12V whereas the high band unit uses +5 and +24V for its pin switches, so the final driver board is completely different between the 2 bands.
The digital interface controlls access to the EEPROM which contains the measurement data, and a way of enabling any of the 7 (or 16) switches in the RF path.
I did open my 85097 (which I use on my 8753ES analyzer) but haven't reverse engineered it other than a conceptual understanding of it taking the signals from the parallel port and using a control line (or maybe register) to multiplex between the A and B ports.?
Following onto answer Steffan's questions,
1.? Yes recalibration this should be possible.?? The contents of the EEPROM are simply the actual S1P measurements for each PIN switch combination, so its a matter of taking a full measurement (on a mechanical calibrated VNA) against each of the PIN switch combinations to get a set of known values.? Note there are only a few standard combinations used? which have been chosen by the design engineers who have a better understanding of the phase delays along the transmission line required for best calibration.
2.? As per #1 above, because you know the complex impedance of the ECal port the VNA will measure the impedance it sees and will de-embed to solve the 12-term matrix for calibration (or 3-6 terms depending on the calibration type selected).???? Instead of a short, open or 50R in the solution matrix we use the known values for the ECal.
It should be noted that the ECal is never a perfect thru, open or short at any time of the electronic calibration.? From memory the short is a few ohms but to "hammer it home" the following 2 PIN's are also energized to ensure there is a stronger reflections.
For successful calibration there must be a ~180deg reversal observed at each frequency (perhaps 90 deg - I know quarter wave is required for unknown through).? This can be easily achieved in the high band cal with the length of transmission line.? For the low band? module there is also a PIN switch halfway through which simulates a open to create a larger phase reversal.
If you have ever used a sliding load during calibration then you will know what I mean by 90 degree observations to get a solid calibration point.
This 180deg requirement is also what sets the lower frequency limit of 45MHz for our units.? As noted in Joels book more modern ECals use a GASFET switch which allow for a more traditional SOLT standard at lower frequencies.
The Arduino board I built is able to reprogram the EEPROM but I haven't added that into the code.? The datasheet wasn't an easy read at the time! ?? After dumping the contents I found the ECals to be better than what I can achieve mechanically, so if I re-calibrate mine it would be a step backwards. ? Given I don't posses a 4 receiver VNA and lower grade test cables my calibrations will always be inferior.
Finally I believe there must be a version of firmware for the 85060C which supports the calibration process.? This is based on the references in the dumped EEPROM data.? Maybe its hidden in the current version somewhere.? If anyone is able to get a copy it would be greatly appreciated.
--
Wayne
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Re: HP-8753E Power Cycles at Start Up
Burt:
Probably will end up doing that. I had a spare SMPS for the rig, and that is doing the job for now. I have the A15 open and on my desk. When I get back to the office on Monday, I will start looking at the filter capacitors.?
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On Aug 28, 2022, at 12:54 AM, Burt K6OQK <biwa@...> wrote:
?Rich,
I have cured a lot of weird problems by fixing the obvious things first.? I suspect that if you were to re-cap the power supply module you would be pleased.? That's been my experience in 90% of the symptoms you describe.
Burt, K6OQK
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Re: "ADDITIONAL STANDARDS ARE NEEDED" when using E-Cal
Hello,
Hope not being too far off topic with two questions.
1. If the ECal module drifts, wouldn't one solution be to simply re-characterize it? I believe this is standard procedure on the newer ones (more or less) whenever one wants to use a configuration different from factory setup.
It would be interesting if anyone with a known 'broken' performance could test writing to Flash and see if at least the communication works.
2. Although the format of the 85062 is not too complicated (reading out content and comparing with measurements seems to give a good match), the actual data stored doesn't make enough sense to be used on its own. Does anyone know the details of how the calibration is performed? As Wayne pointed out, it is likely some kind of hybrid TRL/TRM version, but does anyone know the details? The app notes I have seen don't go too deep into details...
Regards,
? Staffan
PS. I noticed the document regarding 85062-60006 I uploaded earlier wasn't the latest version so I added thT. Don't know if I can or should delete the previous???
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Re: HP-8753E Power Cycles at Start Up
Rich,
I will second Paul's suggestion. I had an HP3586B that developed strange problems.? The big Molex connector between the power transformer and the mother board looked fine... until I turned it over.? The bottom side was black.? I replaced the connector by hard wiring directly from the transformer to the motherboard.? In my case I put about a foot of service loop in a coil tucked between the transformer and the motherboard.? My 3586B has been working flawlessly since doing that; about 10 years ago.
Burt, K6OQK
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Re: HP-8753E Power Cycles at Start Up
Rich,
I have cured a lot of weird problems by fixing the obvious things first.? I suspect that if you were to re-cap the power supply module you would be pleased.? That's been my experience in 90% of the symptoms you describe.
Burt, K6OQK
|
Re: HP-8753E Power Cycles at Start Up
Hi Peter:
There was one thing I negated to mention. I am not sure if it was from a temperature DELTA caused from opening the enclosure/chassis or not, but I did reseat the molex connector which attaches to the Motherboard. While this allowed me to get through the boot sequence but, all kinds of strange errors started to appear. The one most seen was related to the source not being found (forget the exact text).?
I have seen a very similar problem in a Tektronix 2400 (2440) series scope PSU. The problem was on the secondary side of the SMPS, and was caused by a high precision current sense resistor drifting out of tolerance. This caused the scope to recycle much in the same manner as I described with my 8753E. These resistors were there to sense an overcurrent condition, and shutdown the scope in order to save it. That one took me forever to figure out, because I did not realize the tolerances needed to be so tight, and with a normal hand held DMM everything looked OK. I needed to see another decimal or two, if memory serves me.
I looked briefly in the Post Regulator assembly, and I did not see any such resistors. The caps looked ok (physically speaking), as in they had not spewed their guts, or swelled based on my physical inspection of them.?
As I stated, I am going to look for ripple, as that would tell me a lot.?
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On Aug 27, 2022, at 8:06 PM, peter bunge <bunge.pjp@...> wrote:
? I am sending my repair log private. This same thing happened in Sept 2019. For those interested this is a summary ¡¤????????
At
turn on all the front panel displays flash on and off continuously.
¡¤????????
On
the rear of the instrument the top red LED flashes in time to the fan surges
and the bottom green LED stays on. The A15 pre-regulator is probably OK.
¡¤????????
All
green LEDs on A8 are flashing. There is probably something loading one of the
power supplies.
¡¤????????
?Pull A9, A10, A11, A12 and the power supplies
are OK. Start putting them back one at a time.
¡¤????????
OK
until A9 is replaced and the problem returns. A9 capacitors all seem OK but A9
drives the display. Pulling the connector on the display driver board (molex
connector) removes the problem. Everything pointed to the Newscope LCD but various tests running it on a separate power supply were inconclusive. Conclusion:
It is
unlikely that the LCD display was the actual problem. There may have been a
marginal overload somewhere in the 8753B and the LCD current pushed the total
past the trip point.
The
problem could also have been that the trip point setting had shifted for some
reason to a level that tripped when the LCD was finally connected. The LCD only draws current from the +5v power
supply so this is where to look if the problem returns. A test
load was made to replace the Newscope9 if the problem re-appears.
It will
draw 100mA more than the Newscope 9 from both the +5v and +15v supplies and can
be easily modified.
I will report back here when I find the problem. Peter
On Sat, Aug 27, 2022 at 7:38 PM Rich Miller via <av8torrich= [email protected]> wrote: Hi Peter:
When I get a few moments to take a look with a scope I will. This problem seems very much temperature related. My plan is to let it run for a good couple of hours, and then probe the A15W1 Feedthrough points on the SMPS.?
My only concern is, I may not see a lot of ripple with the SMPS unloaded. I have had two cases in various instruments where the switcher fooled me like this. It was not until I loaded it down did I begin to see a lot of ripple.? ? Rich; I would be interested?in what you find. I plan on putting my 8753 on a variac to run with lower voltage. If it was a failing reservoir?capacitor in the pre-regulator this should show it up. The other thing to check is to 'scope the ripple on the pre-regulator. Keep me informed. Peter. On Sat, Aug 27, 2022 at 7:16 PM Rich Miller via <av8torrich= [email protected]> wrote: Peter:
I have it back and running. It was the A8 board, despite the service manual pointing to the post regulator board. I replaced the SMPS, and I am back in business. I opened the SMPS, and did not find anything out of the ordinary. I may plug this in, leave it sit for a few hours, and then begin probing the output.? ?Hi Peter:
Have an update for you. The fault started again. If you follow the troubleshooting guide on Section 5-8 - Page 271 it would leave you to believe I have a post regulator problem (A8).? Swapped A8 out, and the problem precise. When I unplug A15W1 from the post regulator, the problem disappears. Being that I have a known good post regulator board to swap out, I think the problem is the A15 Pre Regulator (SMPS). Getting ready to swap that out and see what happens. ? ? Rich; I think this is a case of "nothing works Thursday". It happens sometimes and maybe this only applied to 8753s. The electronics Gods work in mysterious ways. I read the manual and it says surging is the post regulator circuit sensing an overcurrent and shutting down the power supply repeatedly to protect it. Maybe a cap reforming after months of non use? I had disconnected the S-Param Test set and thought it may have been the culprit but reconnecting it made no difference. It still works. Peter On Sat, Aug 27, 2022 at 2:02 PM Rich Miller via <av8torrich= [email protected]> wrote: LOL - I just got to my office with a replacement PSU, and Post Regulator Board. This was an hour drive.?
?Turned on the VNA, and its fine now. This maybe temp related, so I am going to run some more measurements and wait for the fault to manifest once again. A little annoyed, but such is life I suppose.
I was in the middle of an important measurement when this happened yesterday, so I am going to take it while I can. I will keep you updated, as I learn more. Rich ? I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours? My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
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Bruce Lane
Dr. David Kirkby, Kirkby Microwave Ltd
Burt K6OQK