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E4402B SA power problem - need DC socket connections
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I have an E4402B spectrum analyser with an odd power fault.? The SA powers down after about 10 minutes, but works fine up until then.
(It has been working well in the past but has been unused for a year or two.
I want to try powering it from 12V DC to see if that makes any difference.
Does anyone know the polarity of the two-pin connector on the rear?
And I assume that no-one has rea;l schematics for this unit.? I can't find them anywhere.
The service manual has just block-level detail.
And could a failing Snaphat battery on the CPU board have any effect on powering up and down?? It's 7 years old according to the sticker.
any help gratefully received!
-Jeremy
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Hello Jeremy,
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The 12VDC cable kit has the part number E4401-60066. Sometimes they appear for sale on eBay. I don't know the polarity of the pins but you can check with a multimeter which pin is the Ground pin and the other one will be the +12VDC. Maybe the Ground pin is not the same as the chassis ground but you can try, otherwise you will need to open the case and check the PSU PCB to see which one is the Ground. The Snaphat battery will not create such issues that you experience with your SA. As for schematics they are available at Artek but the PSU is not included in that CLIP. Regards, Razvan On 22/03/2025 18:46, Jeremy Owen via groups.io wrote:
I have an E4402B spectrum analyser with an odd power fault.? The SA |
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Power-down is now fairly random - anywhere from 2 to 10 minutes.? I've replaced the CPU board SnapHat with a much better one (3.2V vs 0.5V!) and that seems to cure some of the oddness on startup (data out of range etc).
But a secondhand psu is $500 and up!? BTW the SA powers up perfectly again if I hit the on-button straight away, so it's hopefully not some sort of heat fault.? Maybe I need to shotgun the caps in the psu, or at least check all ESRs properly.
If anyone has any ideas about this power supply repair please let me know!
-Jeremy
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On original question +ve to top see image of mating connector viewed from "flat" side.
On PSU issue generally they are such a pig to get out and apart it is worth replacing all the small electrolytics. The big HV ones are generally OK. Just checking ESR is not enough. I'm not generally a fan of "shotgun" electrolytic replacement but decided to do it on the very similar PSU in my 8920a (worth looking at the 8920x PSU diagrams there aer some on the web). when I had it out following a main switch transistor failure. While all the caps looked OK and checked for in-circuit ESR (several are in parallel) 3 had started to leak th in one case the PCB was starting to burn.
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Robert. |
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Thanks Robert.? That ties up with about 16.5V to chassis measured on that top pin.? The bottom pin seems to float.
I'll try it on DC and see if that makes any difference.? I think that there's some logic or a microprocessor in there that organises shutdown.
But I'm resigned to a shotgun cap change as this is a really lovely SA in excellent condition and I would like to get more use out of it!
I suspect that it's one of the caps round the startup/shutdown circuitry, but a refresh of a batch of caps may just sort it out.
Thanks for the clear plug info.
BTW does anyone know the correct manufacturer's plug type to match that socket for DC in?? I get lost in the Molex catralogue looking for things like that, and none of my stocks of connector parts matches it.
-Jeremy |
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Well, well, well!? I put 12V on the DC connector and removed the mains and the SA fired up.? about 12V at the plug at 7A when running, from a commercial switchmode 13.8V psu.
And it stayed fired up for 3 hours until I got bored and turned it off.? The display was perfect, no error messages, doing exactly what I expected, which was nice.
This means that the fault must lie in the very first stage of the PSU, where the ac is rectified and down-converted to 15V or so.
Maybe dried-out main reservoir caps giving excessive ripple. or rectifier(s).
I've got other things to attend to now but will get back to this in a week and get the PSU out and some caps changed.
I also used the EEVBlog mechanism to install a narrow bandwidth option "upgrade" and it works beautifully!
Good result all round for now.?
Thanks for the help.
-Jeremy
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The other area of the PSU to look at is standby power and startup circuit. In the older 859x series there is a Schottky diode HSMS-2800 that goes leaky. It's function is to rectify the output from a low current oscillator to generate a pull up voltage for the turn on signal. If it drops too low, the PSU shuts down. Higher temperatures increase leakage, which could cause these symptoms. I don't know how relevant they are, but I posted traced schematics of the 8591E PSU to the files section a few weeks ago. Chris G4MWQ On Mon, 24 Mar 2025, 16:53 Jeremy Owen via , <jezzer3=[email protected]> wrote:
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Hello,
Have a look on the messages " Agilent E4404B Spectrum Analyzer With Dead PSU Repair?" in 2024, it use the same power supply
Best regards
Eric |
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