Agilent 34401a revisions

[Miti]

Is there a reliable source for the VFDs (by themselves) at the moment? I've seen some comments about the aliexpress/ebay ones being a bit hit and miss, and my 34401A VFD is usable but a bit tired, so it would be nice to replace it if there is a source of good new ones. That replacement board is tempting though - would let you build a new display without risking breaking a dim-but-working one in the process!

I just replaced mine with this one from AliExpress:

https://a.aliexpress.com/_mN8vcfI

It’s not exactly what is shown in the picture, it doesn’t say Samsung anywhere, but it works well and the price is reasonable, 53.62 CAD including shipping.
Attached are the pictures before and after.

Cheers,
Miti

[NoisyBoy]

Looks great, best price I have seen yet.

[Hydron]

Yeah thanks for the tip Miti, I assume it appeared brand new as claimed? Results suggest so!

[charlyd]

did somebody export V11 from the chip already to a file?   as Agilent/Keysight is not distributing as coromonadalix stated in his post #1

maybe post more FW updates if worthless, for different generations i saw v10 already.  ( i did investigate it yet but isn t is a matter of a programmer? )

[Hydron]

IIRC v11 is available on xdevs

[Miti]

Yeah thanks for the tip Miti, I assume it appeared brand new as claimed? Results suggest so!

Yes, it does look brand new but the pins are tinned a bit sloppy. I assume the pins are made of a material that is not easy solderable, that's why they have a method  to tin them and that's why it looks like it was soldered before but as you said, the results suggest brand new. We'll see how long it lasts. I kept the old one, just in case.

Miti

[NoisyBoy]

All the ones I saw are new, but of varying quality. Keep us posted on how it holds up, my guess is they will be fine unless you leave the display and equipment on continuously.

I also notice the color has more yellow in it, but the fact it fits well and evenly lit is what really matters.

$28.79 delivered to the US, I am ordering one as I may need one for my two 34401A some day.

[Hydron]

Thanks Miti, just placed my own order for one, will also keep my (usable but a bit tired) old one as a backup.

[dorkshoei]

I bought two of the new "Samsung" marked ones off aliE.  I doubt they are made by Samsung.

Both were fine.

Buy from the seller with the most #orders and then most #reviews of the specific product.

They're all buying from wholesalers and so it's a lottery.

[gerryc89]

Yeah thanks for the tip Miti, I assume it appeared brand new as claimed? Results suggest so!

Yes, it does look brand new but the pins are tinned a bit sloppy. I assume the pins are made of a material that is not easy solderable, that's why they have a method  to tin them and that's why it looks like it was soldered before but as you said, the results suggest brand new. We'll see how long it lasts. I kept the old one, just in case.

Miti

If you have difficult to solder on a metal that create  problems of oxidation you can use the chloridric acid saturated with zinc, a little bit on the pins and the solderability increase immediatly,
Gerry

[Miti]

I also notice the color has more yellow in it, but the fact it fits well and evenly lit is what really matters.

Nope, it's my phone camera or probably different lighting. I compare it to another meter with genuine Itron VFD and I cannot see any difference in color, but the new one is brighter.

[Swainster]

Yeah thanks for the tip Miti, I assume it appeared brand new as claimed? Results suggest so!

Yes, it does look brand new but the pins are tinned a bit sloppy. I assume the pins are made of a material that is not easy solderable, that's why they have a method  to tin them and that's why it looks like it was soldered before but as you said, the results suggest brand new. We'll see how long it lasts. I kept the old one, just in case.

Miti

If you have difficult to solder on a metal that create  problems of oxidation you can use the chloridric acid saturated with zinc, a little bit on the pins and the solderability increase immediatly,
Gerry

In the UK, you can find this solution, or something similar, under the name "Bakers No 3 Soldering fluid". It's pretty strong stuff, so after tinning the leads, I'd make sure the new panel was very well washed/rinsed before bringing anywhere near the 34401A display PCB.

[GigaJoe]

bought ver 03-01-01 ,   LM399 on socket, VFD almost dead, green screen missed, quite scratched, but all work ... should i solder LM ? ...  I think so ...

[razvan784]

The LM399 is socketed on all revisions. It is not a plain LM399 but it is aged and selected. I wouldn't touch it with a soldering iron, the heat might throw off the calibration and affect long-term stability.

[coromonadalix]

MMM  i would say  on the 3  34401a meter i have / had, the lm399 where not socketed  ... all of them have been opened

they where the series with all red input plugs  .... but not having the unobtanium display driver  rev  7 ......

[razvan784]

It's right there in the service manual parts list.
U403 is the voltage reference.
US403 is the socket, hp p/n 1200-1672, mfg p/n SBL-041-SP122-TG30.
Please don't put a hot soldering iron near a precision reference!

[Swainster]

I've got two of the later version (agilent branded), and both have socketed references. In fact, someone had nicked the reference out of one of them before they got to me. I've also have an earlier HP branded all red jack version. I've not had it open yet, as it's never shown a problem, but maybe I'll take a peak inside and report back.

[GigaJoe]

the heat might throw off the calibration and affect long-term stability.

and possibly exorcised Agilent soul that usually adjust temperature and Sebeck effect  
frankly, in such current state of device, worried about Vref jump to a few microvolts.... naaa
i do adjustment when 6 digit running constantly at least 6-9 month.  and that particular unit need a board clean up , it has some current leakage. when Gohm mode on

[Miti]

I keep seeing Service Note 34401A-06 mentioned in various posts but I can’t find it anywhere. Do you have a link or can you attach it here?

Cheers,
Miti

[coromonadalix]

took 3 seconds to find it loll


34401A-06
SUPERSEDES: None
Continued
DATE: January 1996
34401A Multimeter
Serial Numbers: 0000A00000 / 9999Z99999
Display assembly replacement requires compatible firmware.
To Be Performed By: Agilent-Qualified Personnel
Parts Required: See below
Situation:
Display segments may degrade with time. Service action is appropriate if it becomes diffi-
cult to read the display from a distance of two meters. Either replace the display assembly
or replace the display itself.



Page 2 
Service
Solution/Action:
Replace the display assembly with a compatible assembly or replace the display. The
display, P/N 2090-0296, is a vacuum fluorescent display and is a through-hole part with
34 leads.
Compatibility between display assemblies and the main assembly is determined by the
version of firmware installed in the product (firmware version for a 34401A determined
by entering the SYSTEM MENU and on the COMMAND level moving across to
8:REVISION and down to display the Version).
Assembly/part 34401-66502 34401-66512 2090-0296
(description) (Front Panel pc (Front Panel pc (Display, Vacuum-
Assembly) Assembly) Fluorescent)
CompatibleFirmware Version: 06-04-01 Version: 06-04-02 Version: all
and lower and higher

[Miti]

I tried Google and DuckDuckGo and no one can find any of these service notes. 

[Hydron]

First link on Google (to a PDF hosted on eevbog) for me

[Miti]

First link on Google (to a PDF hosted on eevbog) for me

I think Google is playing funky with me. I tried again, it finds this one posted by coromonadalix yesterday and nothing else. DuckDuckGo doesn’t even find this one. They find service and user manuals galore but no service notes. I think we see different results based on the region? Can you find other service notes, 34401A-08 for example?

[coromonadalix]

loll this one just popped this text   with notes in it ??

11-05-02
Agilent
Gray Shift button
Black and red terminals
Serial MY4xxxxxxx
Manufactured 2005
Main board 34401-66511 REV 003
Blue Meder Reed relay

10-05-02
HP
Gray Shift button
Red terminals
Serial US3xxxxxxx
Manufactured 1998
Main board 34401-66501 REV D
Red Coto Reed relay

07-05-02
HP
Blue Shift button
Red terminals
Serial 3xxxAxxxxx
Manufactured 1995
Main board 88809F 34401-66501 REV B
Red Coto Reed relay

05-01-01
HP
Blue Shift button
Red terminals
Serial unknown
Manufactured 1995
Main board 88809F 34401-66501 REV B
Red Coto Reed relay

Fuses (not specified in the service or user manual):
F7A Littelfuse 314
F3A Littelfuse 235
T250mA Schurter FSD (early units might be installed with T125mA for line
voltages >=220V AC (as are Keithley 20x0 units for these voltages))

The 34401a CPU FW can be written to the same FLASH EEPROMs that also work for
Keithley 2000 and 2010: SST39SF020A-70. An upgrade generally requires
desoldering of the CPU FW ROM and (if you are a risk-averter) mounting of
a 32-pin PLCC socket. Some FW upgrades benefit from an EEPROM content
upgrade as well (or it might be necessary) - see below.

According to HP Service Note 34401A-06, the front panel assembly
34401-66502 works with firmware 06-04-01 and lower. 34401-66512 works with
06-04-02 and higher.

The latest code AFAIK is 11-05-03. XX-ZZ-03 is for the third generation of
front panel assembly that is a direct replacement to -02. It is unclear if
it also is compatible to units that were using -01 (but at least from
05-01-01 it can be upgraded to XX-05-YY).

As main board 88809F 34401-66501 REV B is used for both 05-01-01 and
07-05-02, the communications processor can be upgraded to version
XX-01/02/03/04-YY to XX-05-YY. (This code can AFAIK not be downloaded.)

The EEPROM structure looks the same from 07-05-02 to 11-05-02, so no
calibration seems to be necessary when upgrading FW from 07-05-02 to
11-05-02.

The EEPROM structure of 05-01-01 is different from 07-05-02, but it seems
that overwriting EEPROM of 05-01-01 with EEPROM of 07+-05-02 works
(although calibration is definitely needed afterwards).

Service note 34401A-07 says that communications processor XX-03-YY and
XX-04-YY suffer from RS232 error and an upgrade to XX-05-YY is
recommended.

Service note 34401A-08 says that communication processor XX-02-YY,
XX-03-YY, and XX-04-YY suffer from a GPIB error and an upgrade to XX-05-YY
is recommended.

Service note 34401A-09 says that CPU FW 06-AA-BB in some units suffers
from an "erroneous overload" error and an upgrade is recommended in this
case.

[coromonadalix]

and found theses