[volt-nuts] Two 4338B high resistance meters fail on the same range - Keysight can't adjust EEPROM of either.

Wed May 2 06:08:55 EDT 2018

Perhaps if you share EEPROM P/N we can understand why KS cannot replace or update it?

On May 2, 2018 5:37:23 PM GMT+08:00, "David C. Partridge" <david.partridge at perdrix.co.uk> wrote:
>My bet is that they've lost the "secret sauce" for updating the EEPROM
>:(  So it's measuring as best it can with no calibration adjustments
>stored.
>
>Dave
>-----Original Message-----
>From: volt-nuts [mailto:volt-nuts-bounces at febo.com] On Behalf Of Dr.
>David Kirkby
>Sent: 02 May 2018 00:47
>To: hp_agilent_equipment at yahoogroups.com; Discussion of precise voltage
>measurement; RSGBTechnical at groups.io
>Subject: [volt-nuts] Two 4338B high resistance meters fail on the same
>range - Keysight can't adjust EEPROM of either.
>
>I"m pulling my hair out over an identical problem on two instruments. I
>am
>hoping someone might think of a possible cause I have not thought of.
>Sorry
>the post is a bit long, but this is not any easy problem to describe.
>
>I have an Agilent 4339B high resistance meter. This instrument
>essentially
>consists of a variable power supply (0.1 V to 1000 V) and a very
>sensitive
>ammeter. It works out resistance using Ohms Law. It can display
>resistance,
>current, surface resistively and volume resistively.
>
>The service manual states there are no adjustable components in this -
>all
>calibration is performed using software that updates an EEPROM. The
>EEPROM
>is on the CPU board.
>
>This was sent to Keysight in the UK for a firmware upgrade and
>calibration.
>They updated the firmware (stored in a ROM), but the 4339B failed
>calibration.
>
>* All the output voltages from the internal PSU were within
>specification.
>
>* The 10nA current range was slightly out of specification. It was
>reading
>about 0.8℅ high, but the specification is about +/- 0.6%, so it was
>only
>slightly out of specification. (All other ranges were within
>specification,
>but some were not far from the limits. One range might have been 0.5%
>off)
>
>I think the full scale of the current ranges are 10 pA to 100 uA, so 10
>nA
>is not at either extreme.
>
>* All resistance measurements were within specification. (Keysight test
>up
>to 1e11 ohms,   but it can read up to 1.6e16 ohms. I guess they simply
>can't get accurate resistors above 1e11 ohms).
>
>Calibration at Keysight includes any firmware upgrades if you request
>updates.  It also includes the cost of any adjustments needed - unlike
>most
>calibration labs.
>
>Keysight said the EEPROM could not be adjusted to bring the 10 nA range
>within specification, so it needed a new CPU board. I never received a
>formal quote for repair, but I was told about £2000 (GBP), which seemed
>a
>lot considering the CPU board is about $600 (USD) from Keysight.
>
>These meters sell for around $3000, but other instruments available for
>far
>less use the same CPU.  I was intending repairing my 4339B  by swapping
>CPU
>boards from a cheaper instrument, and using a new  EEPROM, just in case
>it
>was the EEPROM faulty, as that goes in a socket on the CPU board.
>
>However, I  managed to find another 4339B at a good price, so that was
>purchased and plans to repair the first instrument were put on hold.
>
>
>I asked for a quote for calibration based on it having a blank EEPROM.
>I
>thought this would be advantageous, as Keysight could put each range
>"spot
>on". I expected the cost to be a bit higher but it was not.
>
>Much to my surprise, the instrument worked and seemed reasonably
>accurate
>even with the blank EEPROM.
>
>I sent this second 4338B to Keysight for calibration. A couple of days
>later i received an email from Keysight telling me the second 
>instrument
>has a fault. The fault is on the 10 nA range (as the first instrument)
>and
>the EEPROM can't be adjusted (like the first instrument). This time it
>is
>reading about 0.7% low, which is not much out considering the
>specification
>is about +/- 0.6%.
>
>So I now have two 4339Bs, both being within specification on all ranges
>except 10 nA, and neither being adjustable! So naturally I queried why
>both
>instruments appear to have the same fault.
>
>I then received an email from someone st Keysight who had noticed I
>said
>the EEPROM was blank. He asked where did I get the EEPROM from. LUCKILY
>I
>had bought the EEPROM directly from Keysight,  despite I could have got
>s
>very similar one from Mouser for a tenth of the price or a supposedly
>identical one for even less from China on eBay.
>
>I am hoping to speak to someone at Keysight  tomorrow,,  but does
>anyone
>have any ideas what could cause two instruments to be slightly out of
>specification on the same range, but neither instrument will allow them
>to
>update the EEPROM?
>
>Note one instrument reads high and the other low. I can understand that
>perhaps the resistors used in the current to voltage converter on the
>10 nA
>range might be a bit less stable than used on other ranges, but I can't
>understand why Keysight can't bring the meters in spec just by updating
>the
>EEPROM.
>
>
>
>Dave
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