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Date
Re: DIY: Repair of HP Step Attenuators

 

Here’s a YouTube video I found when I was repairing the attenuator in my 8902a. ?I followed his procedure and used the same watch repair o ring kit from Amazon (under $10 shipped).

HP CRT "rough" equivalence info needed

 

I got a HP8754A recently that mostly works but seems low on available trace intensity. Maybe it just needs some internal adjustment, or maybe the CRT is weak on emission. Now that I have this one, I've cancelled a project I was planning to fix an old HP8407 VNA with 8412A CRT mag/phase display. I junked it all out and it turned out to be the right choice, since I found all sorts of corrosion in places inside, and broken items, which would have been a PITA to restore anyway. I would have also needed to acquire or build a suitable source for it. The 8754A has everything in one unit sufficient for mag/phase transmission measurements on RF parts. It will be committed to the component testing dept.
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I saved the CRT from the 8412A. It seemed to be pretty decent in brightness, so maybe it could be a spare for the 8754A if ever needed, with certain limitations. The screens appear to be basically the same except for marking details, and the 8412A one does not have the circular or radial graticule lines for polar display. In the manuals I found the CRT pinouts appear to be the same, but the listed cathode supplies differ by 100V - could just be typos, or different design choices, or maybe due to different phosphors (P39 v. P7?).
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I believe they are both the same basic CRT, just with different faces, so should be interchangeable. I found some CRT info here in the files department. It says the 8412A used 5083-9081/P7, and the 8754A used 5083-1890/P31. The manual for the 8754A says its standard CRT is P39, while the 8407A doesn't say anything about the phosphor. I know they're both green, and would have gone with long persistence for this application. Anyway, I can accept the differences if something should happen to the original CRT, and the spare is close enough.
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Does anyone know details of the HP CRT lines, or where more info can be found to clearly determine (electrical) interchangeability?
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Ed
Re: CAL TIMEBASE 8591A

 

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I found the problem, I simply made a mistake in the procedure. Everything is correct now.

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Yves
Re: DIY: Repair of HP Step Attenuators

 

Hi Don I searched as you described but didn't find your repair procedure. What is the message number please? Thanks Jason NJ7K?
Re: 89605 / 89606 cal file

 

It seems the cal files have one gain parameter starting at 50MHz in 50MHz steps. The smallest of the three files must’ve been intended for a system with an E2730 and the others for systems with E2731.
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It seems curious about that there isn’t any attenuator information in the files despite the fact that the 89605 contains one. Perhaps the cal signal loops through the tuner and the actual attenuation is computed.
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CAL TIMEBASE 8591A

 

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Hi,

I have two 8591As to check, and for both, I'd like to correct the timebase.

I followed the procedure in the service manual; it worked, and I correctly executed the CAL STORE command when everything was correct.

This manual matched the firmware version and serial number for both 8591As.

If I perform a PRESET or power cycle, the value contained in this TIMEBASE-related register reverts to the value before I tried to make a change.

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For one, it's a value of 255 because the battery was completely dead.

After changing the battery, I was able to successfully redo all the calibration constants; the only value not saved in volatile memory is the TIMEBASE adjustment.

For the other 8591A, there was already a value, it was 87. If I change this value and save the calibration, also after a PRESET or power cycle, the value returns to 87...where is the error in this procedure?

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Yves
Re: DIY: Repair of HP Step Attenuators

 

Thanks
Just ordered 50 ? orings.? I have 2 Attenuators to repair.
Re: DIY: Repair of HP Step Attenuators

 

How many of what size/type would be needed to replace all the ones used in an 8566B stack? I'd be interested in buying a set to refurbish my spec an when it becomes necessary.

DaveD
KC0WJN


On Wed, Mar 26, 2025 at 15:29 John Griessen via <john=[email protected]> wrote:
On 3/26/25 10:18, Don Bitters via wrote:
> you will find a detailed step by step procedure with HPAK part nos. and Apple Rubber part nos. for the o-rings.

Is anyone going to be buying 0-rings now?? I'd like to do a group order since I now have an old, mostly working 8566B SA.
These can be mailed around in letters for $.73...
Re: DIY: Repair of HP Step Attenuators

 

On 3/26/25 10:18, Don Bitters via groups.io wrote:
you will find a detailed step by step procedure with HPAK part nos. and Apple Rubber part nos. for the o-rings.
Is anyone going to be buying 0-rings now? I'd like to do a group order since I now have an old, mostly working 8566B SA.
These can be mailed around in letters for $.73...
HP 435B, Zero Carryover Test - How noisy should it be?

 

Hey All,
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I noticed what looked to be a zero issue with my 435B, so I thought I'd run it through the zero carryover test (OSM 4-6) to see what was going on.
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While the meter meets all the ranges given for zero carryover, it occasionally doesn't meet the requirement:
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4. Press the front panel ZERO and wait for the meter indicator's position to stabilize. Verify that the DVM reads 0+/- 0.9 mVdc. Release the ZERO switch.
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My output seemed quite noisy, so I used the statistic function to look at it over 100 samples, and what I saw was:
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  • Max 0.533 mVdc
  • Min -1.006 mVdc
  • Avg -0.150 mVdc
If I had been quick to look at it, then I could have moved on to the next part of the test and never noticed that over some time it exceeds the +/- 0.9 mVdc requirement.
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Should this be less noisy??
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The only fix from the manual is to change the factory selected resistors A4R12 & A4R16 (the A1 assembly is a recommended factory replacement), and it does pass the actual +/- span for each step of the range control so I'm hesitant to make any changes to those.
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Any thoughts or guidance appreciated.
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TonyG
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Re: DIY: Repair of HP Step Attenuators

 

I used 0.5mm CS X 1.0mm ID 70 durometer from theoringstore.com on an attenuator from my HP 8560A
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They are 0.22ea. with a $5.00 minumum order and shipping runs $9.95 so you will have to order 22 to meet their order requirement.
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I'd order extra and store them in an airtight bag. They are really tiny!
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Sam
W3OHM
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Re: DIY: Repair of HP Step Attenuators

 

I have done over a hundred repairs of the 3332xA/B style attenuators. In the file listing in this site you will find a detailed step by step procedure with HPAK part nos. and Apple Rubber part nos. for the o-rings.
You may search the files by my name, or HP 8566 attenuator repair, HP attenuator repair, any of which should find the file.
The short of it is with the attenuator lid off and the contacts in the up (closed) position push the push rod toward the ball opening in the contact slot and lift the contact off from the push rod, when you have them all disconnected pull the solenoid down to the open position. Then you can push the push rods out of the solenoid slots replace the rubber o-rings and put them back into place, reversing the above procedure.

Don Bitters
Re: DIY: Repair of HP Step Attenuators

 

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The original o-rings were 1.0mm ID,2.2mm OD for a cross section of 0.6mm.

None of the ones listed are exactly the correct size.?
Re: DIY: Repair of HP Step Attenuators

 

There's good older threads that go into some detail on this. I repaired one set a few years ago, posting here, and I recall the "surgery" aspect of the project. Mechanically, maybe one of the more demanding projects in this type of work. I used watch o-rings, but there are more appropriate materials and sources of o-rings for this specific purpose.?

I was also able to find a very good video of the procedure on youtube, and I think there are several others available.?

Good luck with the project.?

Radu.?


On Tue, Mar 25, 2025, 11:40 AM ROBERT LEVY via <boblevy4321=[email protected]> wrote:
HiI just disassembled my hp8648 attenuator 33322-60011.
I found the little rubber orings have broke.
I need to know exactly how to disconnect the rods that the orings are on from the contact, without breaking anything.
Thank you to ? Microwaveengineer1968??? for an excellent write up.
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I found this link to the orings ? ?
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Thank you
Bob
Re: DIY: Repair of HP Step Attenuators

 

Which size should I select on that page?
I have stuck attenuator sections in three different instruments, seems to be a common problem.
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Marko Cebokli
Re: DIY: Repair of HP Step Attenuators

 

HiI just disassembled my hp8648 attenuator 33322-60011.
I found the little rubber orings have broke.
I need to know exactly how to disconnect the rods that the orings are on from the contact, without breaking anything.
Thank you to ? Microwaveengineer1968??? for an excellent write up.
?
I found this link to the orings ? ?
?
Thank you
Bob
Re: 89605 / 89606 cal file

 

Awesome and thank you!
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I bricked two E1439C digitizers from a bad firmware update and developed a procedure to fix those.
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I need to write a small program to reset the serial number.?
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The A1 (main board) cal date is also lost. The A3 cal date is retained (on a 23C02 I2C EEPROM).
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I wonder if the A3 board has attenuation data.
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On the A1 board, I don’t see much for adjustments. Being an ADC, if the voltages for references are correct they don’t require adjustment. If they’re wrong then that’d be a repair. I recall seeing a counter le markings for capacitors. I’d guess in the same way as an (Tektronix) oscilloscope having a lug to clip a probe onto and the probe having a couple of trimmers to adjust for minimum under/overshoot, perhaps the only necessary adjustment is the input termination to achieve minimum harmonic distortion of a sine wave, and with a square wave input, a specific ratio of relative power levels.
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The VISA API has no documented call that I’ve seen for updating cal dates.
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i don’t suppose anyone has seen a calibration procedure for the E1438/E1439, but it’d be great if someone could confirm any of my suspicions.
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I plan on sharing some cliffs notes and raw flash images extracted from an E1439A and the image I put on the E1439C to unbrick it.

what worked for me to not brick after putting the image on there was to have edited the model number and serial information before resoldering the chip, and then upgrade to B.01.02 firmware and then B.02.01 firmware (the versions might be different depending on serial range).
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I don’t know what all the differences are between the E1439C and E1439A, but I did notice a 1.2V SOT-23 reference attached to two pins of a CPLD and the third lead had a short wire attached to a third pin on the same.
Re: HP3325A Trouble, Calibration FAIL 2 & 3

 

I changed Q219 and its complementary transistor. Now I can adjust the 7.5Volts on F3. The amp is now fixed, but the A-CAL Fail error for square and triangle is still present.
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The output is correct, sync out as well, amplitude into a 50 Ohm load is ok, on sine, square and triangle & ramp
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When switching to ramp function something curious follows: The display goes off, the ramp function is visible on the scope, but it 'sweeps'.
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Picture 1: relay board, relays are clickking, are these types they reliable? The yellow relays are often mentioned to be cleaned, my could not be opened.
Picture 2: sinus 1kHz, lokks as expected.
Picture 3: ramp moving with about 0.5Hz.
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here is a video: shows the moving of the ramp and then flips to the correct curve? for a second.
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Outputs at the analog switches are as expected, all voltages as well.
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The self test works except the AC fail, FAIL 2, FAIL 3
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The manual says this is 60% of the controller.?
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Any advices waht to test now? ROM/RAM?
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Or has anyone spare? boards for the 3325A to exchange and for testing ?
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IMG_9335.MOV
IMG_9335.MOV

Re: Intermittent REF UNLOCK error message on 8591A Spectrum Analyzer

 

Hi Anders
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Just go to the Files section i have been uploaded the Clip to 8590/91A
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Br
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Johnny
Re: E4402B SA power problem - need DC socket connections

 

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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