EEVblog #933 - Keysight U1272A EMC Issue

[Zbig]

[..]because the Agilent U1273A is only about half a year old and has merely seen one hour of on-time (don´t ask why ), so Oled ageing would not be my first thought.

Impossible. My affected U1273A is two years old and is already branded Keysight.

[Zbig]

Regarding the OLED brightness differences: have you guys tried invoking the OLED self-test screen? If you hold Trig/Auto/Hold when powering on, all the pixels will illuminate. I too noticed some differences between my old and new Keysight U1273A but nothing dramatic. When you look at the selftest screen, you can actually see the sections which are often/always active differ in luminosity from the surrounding ones. Funnily, last time I checked, in mine it appeared that the more often used ones were actually brighter; kind of a "reverse burn-in".

[wraper]

If we can do the calibration ourselves , then we could just stick with the zero ohm resistors.  Instead of using the 0.2 ohm resistors.

Yes, but we don't know if it is possible to calibrate only the short values or if all the resistance values have to be calibrated.
Nobody (me included) seems to be brave enough to risk the factory calibration. 

When I have a spare time, I might dump calibration if it is located in some sort of EEPROM IC, and then experiment with CAL. Don't know how soon that spare time will happen, though.
EDIT: took it apart, EEPROM is AT24C512C. So guess will be pretty safe to experiment.

[M8A4X]

[..]because the Agilent U1273A is only about half a year old and has merely seen one hour of on-time (don´t ask why ), so Oled ageing would not be my first thought.

Impossible. My affected U1273A is two years old and is already branded Keysight.

@Zbig: You are right, the MFD of the "Agilent" unit is end of 2014, bought it about half a year ago from a local electronics shop where it was sitting on the shelf (new, unused). It had a Keysight sticker in the box, but the label on top of the screen says Agilent.
Sorry for the confusion   And thanks for the hint about the test screen, I will try this. However, the "old" unit-screen was good enough until now and will be for a long time, especially considering my "heavy usage" 

[ddrl46]

I will be doing the modification on a U1273AX by replacing BD4,5,7 and R55. Since I have access to a Fluke 5522A calibrator I will be experimenting with the resistance adjustment before doing a full adjustment.

[Lockon Stratos]

I just got the replacement. Thx keysight .

Impossible. My affected U1273A is two years old and is already branded Keysight.

Mine is about 1 years old if i remember correctly and its branded as agilent(both on the meter itself and the bootscreen[after the FW update this changed to keysight]...

[voltsandjolts]

I will be doing the modification on a U1273AX by replacing BD4,5,7 and R55. Since I have access to a Fluke 5522A calibrator I will be experimenting with the resistance adjustment before doing a full adjustment.

Have you had a chance to look at this....pleeeeease! 

[Dwaine]

I'm also waiting too see the cal details before ordering the parts.

[ddrl46]

I will be doing the modification on a U1273AX by replacing BD4,5,7 and R55. Since I have access to a Fluke 5522A calibrator I will be experimenting with the resistance adjustment before doing a full adjustment.

Have you had a chance to look at this....pleeeeease! 

I have had a chance to experiment with the calibration and I can quite safely say that all you really have to do is the following (in the same order):

- Perform a short adjustment on DC millivolts then DC volts
- Perform a zero adjustment on the ohms range (short Hi to Lo using a shorting bar and let it run through all its ranges)
- Perform a open adjustment on the ohms range
- Perform a short adjustment on the diode range
- Perform a open adjustment on al DC current ranges

You can probably skip all adjustments besides the resistance short/open adjustment and still be fine, I however did do them because of the simple standards required to perform them.

After doing this and verifying the meter everything seemed fine.

The calibration details can be found in the Keysight U1270 series service guide.

[Iwanushka]

Hi there, can you attach the manual for us who don't know google-fu?

[voltsandjolts]

Thank you, ddrl46.
I understand that you have recommended to do open/short tests on several ranges, probably best practice.
However, does the meter allow me to do a single resistance range calibration point (say, ohms short cal) without having to do any of the other resistance calibration points (10M, 3M, 300K, 30K, 3K...etc)?

The U1270 series service manual is here:
http://literature.cdn.keysight.com/litweb/pdf/U1271-90020.pdf?id=1996089

[elCap]

I just received the U1282A replacement for my U1272A! Thanks Keysight!!
Very nice of them considering my U1272A is about 6 years old. And it's way overdue for a re-cal so it's good time to do the mods of BD4,5,7 and R55 before the calibration.

[Iwanushka]

Guys,

Have you seen this?
Date: 2017-02-13
http://literature.cdn.keysight.com/litweb/pdf/U1282A-02A.pdf

Looks like U1282A has the same issue as U1272A 

[HighVoltage]

Guys,

Have you seen this?
Date: 2017-02-13
http://literature.cdn.keysight.com/litweb/pdf/U1282A-02A.pdf

Looks like U1282A has the same issue as U1272A 

Wow!
So, let me understand this, my U1272A was replaced by a U1282A that now also has a problem?
May be the U1282A will now be replaced by a redesigned U1272A?
Hmm....

[voltsandjolts]

Well, you got to applaude Keysight folks for being open and honest, above and beyond many (all?) other TE manufacturers.
I am absolutely delighted with my U1282A (thank you Keysight) so whatever corner-case EMC has caused a glitch, I reckon I'll be keeping mine.

[TheAmmoniacal]

Didn't a bunch of us test the interference issue on their new U1282A? I'm sure they performed just fine.

Any explanation from Keysight on this?

[HighVoltage]

My new (replacement) U1282A was tested and I have not found any issues at all.
I am very happy with it and totally surprised to see this notice.

It would be nice to have an explanation from Keysight.

[Iwanushka]

Checked a few other meters, looks like only Escort designs have service note : issues with Freq above 80MHz, so maybe all Keysight designs have the same design issue?

PS. did any of you were able to register replacement DMM on Keysight web? I get: Unrecognized Serial Number 

Edit: main question what is below 80Mhz, is it 3MHz or is it 79,99MHz, would be nice to get more details from Keysight.

PS. anyway thumbs up for Keysight for being honest about all the issues/undocumented features, and helping with/solving issues even for devices that are out of warranty!

[bitseeker]

Replacement U1280 meters may not have the EMC issue. Only ones with serial numbers in the range given in the service note. Mine is outside the range specified.

Note that the U1250 series also has an EMC issue. Again, check the serial number range for applicability.

It's interesting that the initial service note for the U1250/U1280 problem covered repair in general. It was then succeeded by repair upon specific failure. I'm not sure what specific failure means. Demonstrable interference (i.e., not all units in the range are necessarily affected)?

[Iwanushka]

The replacement U1280 meters don't have the EMC issue. Only ones with serial numbers in the range given in the service note. Also, the frequency (80+ MHz) is much higher than that which affected the U1270 series. So, if you have an affected meter, it wouldn't have had an issue with the same signal that made the U1270 react.

Note that the U1250 series also has an EMC issue in the same spectrum as the U1280. Again, check the serial number range for applicability.

It's interesting that the initial service note for the U1250/U1280 problem covered repair in general. It was then succeeded by repair upon specific failure. I'm not sure what specific failure means. Demonstrable interference (i.e., not all units in the range are necessarily affected)?

U1252B says above 80MHz,

for U1282A

U1282A Handheld Digital Multimeter
Serial Numbers: MY00000000 / MY56999999

This indicates all DMMs, Replacements that where manufactured just before X-mass have SN MY564...

Edit: Main question why that service note shows serials of all manufactured DMMs

Edit2: you also say that both U1250 and U1280 have EMC issue in the same freq range, well I understand that U1250 above 80MHz is not the same as U1280 below  80MHz; above and below are two opposite things.

[bitseeker]

Yeah, I mixed up the U1250 and U1280 on the frequency ranges involved. Thanks. Fixed.

My replacement U1280 is not in the affected serial number range (MY00000000 / MY56999999).

[TheAmmoniacal]

I guess the language of the service note is rather confusing "below 80 MHz environment". I first read that as the meter having EMC issues at some frequency below 80 MHz, such that it could be in the similar range as the U1272A. But as bitseeker mention it I think he's right, it's in or near 80 MHz. Very few people have to care about this?

[bitseeker]

The language might make more sense relative to the naming of the ranges that are used for EMC testing. I don't know since I'm not familiar with those specifications, but that's the way I understood it.

[Iwanushka]

Yeah, I mixed up the U1250 and U1280 on the frequency ranges involved. Thanks. Fixed.

My replacement U1280 is not in the affected serial number range (MY00000000 / MY56999999).

Well Mine that was shipped on Dec 13 and arrived on Jan has SN MY564... so go figure...

[Iwanushka]

I guess the language of the service note is rather confusing "below 80 MHz environment". I first read that as the meter having EMC issues at some frequency below 80 MHz, such that it could be in the similar range as the U1272A. But as bitseeker mention it I think he's right, it's in or near 80 MHz. Very few people have to care about this?

U1272A has identical service note as U1280 saying below 80MHz, so if we think this way it means U1272A has no EMC issue.

Edit: that writing should be like this: lets say we have spec1 should work at 0 to 80MHz, and spec2 should work at 0 to 100MHz, so below 80MHz means it does not comply with spec1 and spec2, above 80MHz means it complies with spec1 but not spec2

Edit2: anyway who cares as long as it works near LED lights and so on.