Electronics > Metrology
3458A Worklog
MiDi:
This unit is equipped with option 002 and was received with "RAM TEST 1 LOW" error.
It was first powered up on Nov 24th, on Dec 1st it was taken apart for further inspection and cleaning.
Besides a bit of dust on fan & filter it looked as it came straight out of factory.
The datecodes on the ics reveales a manufacturing date from late '89 to early '90.
Remarkable that the calram still seems to be in good condition and maintaining caldata after nearly 30 years.
Obviously it is high time for replacement of the 3 Dallas NVSRAMs - to save the calram a Linux-Tool for GPIB was used.
Next thing to check was heart of instrument: condition of adc (A3-board)
Manual data for cal 72 & 175 was captured between Nov 26th and Dec 9th, since then the acal dc data was captured by script every 5min.
The first two weeks were not promising: the SN18A check revealed drift of > 0.43ppm/day.
It appeared to become a member of A3-sickness club, but fortunately the drift went down to sub 0.01ppm/day for last week :-+
The adc shows a TC of ~0.33ppm, that is below the stated 0.4ppm in HP Journal p. 13.
This seems to be in spec and shows why it is a good idea to do regular acal for precision measurements even in the 10V range - if the lab temperature is not rock stable (which home lab is?).
In conclusion the adc seems to be in reasonable condition after a month of settling and ~8ppm total drift.
In the meantime nvsram, caps and mains filter were ordered.
Late on Dec 27th it went down for replacement of nvsrams and update to latest FW.
This took a bit longer than estimated - as it revealed that uv light for e.g. developing pcbs (UVB) is not good for erasing eproms (UVC) :palm:, but after 24h exposure all bits where cleared and newest FW version 9.2 could be programmed successfully.
After this the device turned on and showed a convergence error once, after reset everything was fine and on several power cycles no error came up anymore.
Things to do:
-ordering special caps (radial 8200µF & big 15mF) and fan
-replacement of electrolytics, mains filter & fan
-investigate input leakage, noise, stability, TC etc.
probably: reduce LTZ1000 temperature set point with parallel 100k to reduce drift even more
EDIT 2019-05-21 (moved table from second to first post):
Overview of replaced parts:
A4 - inguard power supply
part #descriptionpitch [mm]manufacturerreplacementmanufacturerC07, C082,200µF 35V 85°C 18x35mm SMC7.5Nippon Chemi-Con2,200µF 35V 105°C 16x25mm FR Type APanasonicC0915,000µF 16V 85°C 35x26mm SME10Nippon Chemi-Con18,000µF 16V 105°C 30x30mm LGUNichiconC1722µF 50V 85°C 10x11mm 513D3,5Sprague22µF 50V 105°C 5x11mm FR Type APanasonic
A5 - outguard controller
part #descriptionpitch [mm]manufacturerreplacementmanufacturerU121, U122DS1235YW-150 NVSRAM28PDallasDS1230Y-120+ on precision socketMaximU132DS1220Y-150 NVSRAM24PDallasDS1220AD-150+ on precision socketMaxim
A6 - outguard power supply
part #descriptionpitch [mm]manufacturerreplacementmanufacturerC1, C11680uF 50V 85°C 16x22mm SXE7.5Nippon Chemi-Con680µF 63V 105°C 16x25mm LXZ (max 25mm - height limited by case)Europe Chemi-ConC88,300µF 35V 85°C 25x67mm 53D70Sprague10,000µF 35V 85°C 25x61mm TVXNichiconC200, C20147µF 63V 85°C 8x15mm SME3,5Nippon Chemi-Con47µF 63V 105°C 8x11,5mm EB Type APanasonicC202330µF 25V 85°C 10x16mm SME5Nippon Chemi-Con330µF 25V 105°C 8x11,5mm FR Type APanasonicC203220µF 16V 85°C 8x15mm SME3,5Nippon Chemi-Con220µF 35V 105°C 8x11,5mm FR Type APanasonicC15, C162.2nF 250V~ Y2 40/085/56 3,5x13x7mm PME 27110RIFA2.2nF 300V~ Y2 55/105/56 4x13x9,5mm MKPWIMA
Case
part #descriptionpitch [mm]manufacturerreplacementmanufacturerFan60x60x25mm 12V 0.7W powered with 15VPapst60x60x25mm 24V 2.88W 109R0624D4011 (12-27.6V)Sanyo DenkiMains Filter3A 47nF 2x750µH FN 32340Schaffner6A 47nF 2x800µH KFSSchurter
MiDi:
On January, 25th the unit went down for another refurbishment.
It was planned to replace the caps, mains filter and fan, but only caps were replaced for now - explanation below.
There is an overview awailable at bottom with all original and replacement parts that were used - it can be easy copied to favorite spreadsheet program.
Replacing all electrolytic capacitors was straight forward and there were no surprises.
A thick copper wire was used to desolder both pins of the caps at the same time - desolder guns are overrated.
The old caps were quite in good condition as a quick check with LCR-tester revealed.
Just a bit more ESR and loss than replacements - would be nothing to worry about for now, but worth replacement for a couple of bucks for good sleep next years.
A4 C09 & A6 C8 were replaced with next higher value available for best fit - as these caps have wide tolerance, a bit more capacitance would not do any harm.
The hidden yellow C17 on A4 was missed, but will be replaced next time.
The visual check on A6 catched attention on the two 2.2nF Y caps C15, C16 near mains fuse, they look cracked like spider app.
They were dropped for now and are replaced next time - there are already Y caps in mains filter, so this should not be an issue.
Mains filter from Schaffner has no good reputation due to several fails, so better to replace it.
It was decided to do it with remaining things next time, as it would be good idea to drill the rivets with closed case from outside to keep the chips out.
Afterwards the case has to be opened again for replacement and all remaining work will be done in one step next time.
The fan introduced quite some vibrations and has this annoying metal sound similar to old noisy hard drives.
It is supplied with unusual 15V and it was intended to be replaced with 24V type that is rated down to 12V.
When comparing both fans it seems that the chosen one would be reasonable with similar current draw and airflow.
As it turned out there is no standard for the pitch (corrected: the pitch is same) and size for mounting holes of "standard" fans and the screws did hold the replacement fan only slightly.
It is a bit quieter and introduces no significant vibration, but a slightly mounted fan seems no good idea. :--
For now there came no option to mind how to solve this, but it was not intended to put the old fan back without any improvement.
There was fitted a bend copper wire into the slots for balancing and after some fiddling the best position and weight was found to minimize introduced vibration.
Maybe it will be replaced in future...
Another odd thing is a bend top cap for LTZ1000.
Not shure if this is critical and should be fixed, any recommendation?
ADC-Drift test is going on and gave unpleasant surprises, although it is still in spec.
EDIT 2019-05-21: Moved Replacement table to first post.
MiDi:
Time for the last episode: Mains Filter & Fan
The unit went down on April 27th for the remaining replacements (list of parts updated & finalized).
Drilling the rivets of the mains filter was a bit harder than thought - my HP3457A did not struggle that much.
After lots of chips and a bit of brute force it was released from its former job and replaced with new Schurter type.
The new one is a bit longer, but no problem to fit it in its place.
The RIFA MP Y-Caps on board were removed last time and now refitted with WIMA MKP (see attached picture).
Interestingly the time did not improve on size of this types (compared to electrolytic ones), the new ones are thicker and higher - this gives confidence, that they will last long after me.
For the problem with the new fan and its bigger screw holes a simple solution has been elaborated.
Fill them with epoxy (e.g. J-B Weld) and after curing drill them to size of holes from original fan.
(the spacings are identical, corrected statement in former post - I obviously squinted as the picture already showed this)
Although J-B Weld ist tought to be the strongest epoxy, it did not stick enough on cleaned, but unprepared holes when screwing it ::)
After filing the inside of the holes to roughen them a bit, the procedure was repeated with success.
The new fan is not significantly quieter, but the annoying metal scratching sound has gone now.
I decided to fix the bend cap - just to be safe - but it defended to go into its intended form.
Heating multiple times to finally ~200°C and bending it with quite some force to its desired shape, it bended back again after cooling down :box:
Sanding with 600 grid finally it gave up and went flat (picture of assembly of both caps and ref-board attached).
Before:
After:
Last thing was to replace overlooked 22uF yellow cap - just a mere formality (see attached picture).
Hopefully all the sweat comes to a happy end and unit is now in good condition.
The ADC drift actually settled to ~0.035 ppm/day for 3 weeks now, before it stayed at ~0.05ppm/day for two months.
The "noise" generated by acal dc is around 0.1ppm-pp according to cal 72, from this point an acal on my unit would be sufficient every 3 days.
With ~0.33ppm TC of ADC this becomes the mayor drive to perform an acal - at least for every °C change (see attached picture of last 3 weeks).
My unit seems to stop drifting during power down, but soon there will be more data to confirm this.
The measured stability before and after final work against external LTZ1000 showed drift in sub-ppm region - fortunately no unpleasant surprises :-+.
Combined noise/drift (+TC) from unit and external reference are ~0,13 ppm stddev and ~0,5ppm-pp (3 days, 1°C span, 100NPLCs, 7V, acal every hour)
Combined TC maybe ~-0,3ppm/°C, but the external ref is not characterized nor trimmed for TC.
This data is just for reference, this has to be repeated with better setup.
There are a couple of things left for full characterization and to be shure it is in good condition:
-log input noise for the ranges and NPLCs
-check input bias current at different voltages and ranges
-measure TC of whole unit
-calibration
-long term drift
Big thanks goes to the 3458A nuts - especially to TiN and his great articles - with the help of this superb documentation the work was nearly straight forward.
TiN:
Welcome to the club. :-+
Now you need SR104, 732A/B/C and second 3458A.... rabbit hole only starts here... :popcorn:
--- Quote ---The first two weeks were not promising: the SN18A check revealed drift of > 0.43ppm/day.
It appeared to become a member of A3-sickness club, but fortunately the drift went down to sub 0.01ppm/day for last week :-+
--- End quote ---
I would hold the breathe, as sometimes bad A3's give you little tease, before they go back driftin. Don't ask me how I know...
SN18A testing should be done weeks after long offline storage anyway, so you are sure data is valid, and not just initial settling of the unit (which often takes few weeks of 24/7 operation).
--- Quote ---The adc shows a TC of ~0.33ppm, that is below the stated 0.4ppm in HP Journal p. 13.
--- End quote ---
Pretty horrid, if that TC is actually of the unit, and not the measurement setup. I'd say good happy 3458A should be <0.1ppm TC on main 10V range (no ACAL of course).
Dr. Frank:
--- Quote from: TiN on January 07, 2019, 04:31:02 am ---
--- Quote ---The adc shows a TC of ~0.33ppm, that is below the stated 0.4ppm in HP Journal p. 13.
--- End quote ---
Pretty horrid, if that TC is actually of the unit, and not the measurement setup. I'd say good happy 3458A should be <0.1ppm TC on main 10V range (no ACAL of course).
--- End quote ---
Hello TiN,
how do you measure that on your 3458As?
Per specification, about 0.5ppm/°C is the T.C. w/o ACAL, that is mostly the R-ladder matching T.C. of U180, and 0.15ppm/°C is with ACAL, i.e. latter is mostly the LTZ1000As T.C.
I've determined about 0.23ppm/°C for CAL? 72 (i.e. purely U180).
Did an ACAL directly after power-up, in cold state, that extrapolation fits nicely with statistical data.
Combined T.C. of my box is about 0.4ppm/°C.
I think, MiDis 3458A is fine as well.
Frank
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