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Electronics => Repair => Topic started by: lionelkjh on November 23, 2018, 06:52:08 pm

Title: AGILENT 34401A
Post by: lionelkjh on November 23, 2018, 06:52:08 pm
Good evening everyone! I am having a problem with my multimeter AGILENT 34401A. Here are the symptoms of the failure: it starts to light up, all the digits are displayed during the initialization; then suddenly everything goes off. Nothing remains in the display, however we can not select anything on the keyboard; except the SHIFT function that lights up, but accesses the menu. This failure happened suddenly. Does somebody have an idea?? What are the tensions to check? Can the failure come from the front panel? I attach photos and a short video of the failure. Thank you for you precious help! :palm:
Title: Re: AGILENT 34401A
Post by: lionelkjh on November 23, 2018, 07:12:55 pm
a video of 13s is not supported on the site: I can not put it !!! |O
Title: Re: AGILENT 34401A
Post by: lionelkjh on November 23, 2018, 07:29:34 pm
I found the same case similar to the failure: I copied the link: https: //www.youtube.com/watch? V = 8ybhONvIP0Q
Title: Re: AGILENT 34401A
Post by: Mr. Scram on November 23, 2018, 07:33:40 pm
Reposted with corrected link. :)

https://www.youtube.com/watch?v=8ybhONvIP0Q (https://www.youtube.com/watch?v=8ybhONvIP0Q)
Title: Re: AGILENT 34401A
Post by: chekhov on November 23, 2018, 08:00:29 pm
Reminds me this topic https://www.eevblog.com/forum/repair/agilenthp-e3646a-repair/ (https://www.eevblog.com/forum/repair/agilenthp-e3646a-repair/).

There might be a connection problem between display module and the rest of the unit, and shift lights up only because this action is directly controlled by the IC that is on display module.

Have you tried to communicate with unit through RS-232 (if enabled of course) ?
Title: Re: AGILENT 34401A
Post by: vidi on November 23, 2018, 10:53:16 pm
Hi

0.) Schematics/service manual and lot of useful info can be found here https://xdevs.com/fix/hp34401a/
1) Does it beep when you turn it on ? (hint: The buzzer is driven by separate MCU (U700) that is responsible for GPIB/RS232 communication, opto-coupled from main board. It should work / beep as soon as it has a stable power supply and valid data over optocoupled UART with the main processor).
2) Check with an oscilloscope a voltage input and voltage output of U553. The U553 is a voltage regulator that also drives main MCU reset signal. If the output voltage drops below threshold, it forces a reset. It also means that one of  electrolytic caps (C556?) is probably half dead.
3) In general, check with the scope a power supply on each main digital component, then move to trace digital communication between the components.
Title: Re: AGILENT 34401A
Post by: lionelkjh on November 24, 2018, 08:53:51 am
Hello, thank you for your help! The multimeter beep twice at startup, and display nothing, suaf when you press SHIFT (exactly as in the video). The exact version is in the photos that I posted yesterday, the video could not be put because it is in mp4 format. I'll be getting my RT809H soon, maybe I can see more clearly? I'm already going to look at these elements to check ..... Cdt
Title: Re: AGILENT 34401A
Post by: lionelkjh on November 24, 2018, 11:41:56 am
I just downloaded the service manual, and the fault corresponds to error code 601 ......
Title: Re: AGILENT 34401A
Post by: Samogon on November 24, 2018, 05:07:37 pm
Try to reset front panel cable in the molex connector
Title: Re: AGILENT 34401A
Post by: SrS on November 26, 2018, 11:34:19 am
Press Shift then directly Menu (On/Off).
Your display is probably set to off state.

try System menu -> Display -> On
Title: Re: AGILENT 34401A
Post by: chekhov on November 26, 2018, 12:07:12 pm
Quote
Your display is probably set to off state.
Manual says that this state is stored in volatile memory. If I understand correctly, it does not survive power-cycle.

Also, it was not mentioned whether relays are clicking or not.
Title: Re: AGILENT 34401A
Post by: Mr. Scram on November 26, 2018, 12:48:45 pm
I just tested to make sure. A power cycle through resets the display to on, so that doesn't appear to be the problem. It's a fair suggestion though.
Title: Re: AGILENT 34401A
Post by: lionelkjh on November 26, 2018, 01:42:02 pm
Hello everyone! I tried while pressing SHIFT at startup, but the digits all light up and go off, the multimeter emits 2 beeps, then the display remains off. I have raised tensions, and they are good; I strongly suspect U500 to be dead. Here are the voltages: U552 = -18V, U551 = 18V, U553 (pin2) = 5V, CR306 / CR305 (cathode) = 18V, CR304 / CR307 = -18V, CR402 (anode) = -15V; CR401 (anode) = 15V. The 80C196 must be dead, but how to test it to be certain? Is it programmed? or the content of the program is it contained in flash memory ??? Thank you for you precious help :palm:
Title: Re: AGILENT 34401A
Post by: Zucca on November 26, 2018, 06:07:28 pm
Are GPIB and/or serial working? You could get some diagnostic out of there.
Title: Re: AGILENT 34401A
Post by: lionelkjh on November 26, 2018, 06:30:31 pm
I do not have the programmer, I am waiting for his arrival, I will be able to know more after ..... >:D
Title: Re: AGILENT 34401A
Post by: lionelkjh on November 27, 2018, 12:37:37 pm
Hello; could someone have solved this problem on this multimeter ??? :=\
Title: Re: AGILENT 34401A
Post by: corn11 on November 27, 2018, 01:26:15 pm
Hi,

your problem description sounds like the SRAM issue I've had with my 34401A back then:
https://www.eevblog.com/forum/repair/hp-34401a-repair/msg612109/#msg612109 (https://www.eevblog.com/forum/repair/hp-34401a-repair/msg612109/#msg612109)

There is a special error code for that issue mentioned in the service manual which can only be read via GPIB if I recap that correctly.
The 80C196 can also drive the reset line if it hits a reset vector which is the case when the SRAM check fails. It could also be a faulty EPROM or the 80C196 but I doubt it.
If you haven't got a GPIB adapter and checked the usual errors like the regulator I would swap the SRAM to be sure and if this isn't the case I would socket the EPROM and get a new EPROM chip.
The firmware is available on the net in various revisions.


Title: Re: AGILENT 34401A
Post by: lionelkjh on November 27, 2018, 04:55:26 pm
Good evening; the model I have is more recent (2008) and does not have the GPIB but the RS232 ..... :-//
Title: Re: AGILENT 34401A
Post by: HighVoltage on November 27, 2018, 06:15:30 pm
Good evening; the model I have is more recent (2008) and does not have the GPIB but the RS232 ..... :-//

All 34401A have the GPIB and the RS232 interface, this was standard from the beginning to the last model.
I have never seen a 34401A without GPIB, since this is part of the main PCB

Like Zucca said, I would hook up a remote control and see is the instrument reacts to remote commands

 
Title: Re: AGILENT 34401A
Post by: corn11 on November 27, 2018, 06:33:06 pm
Good evening; the model I have is more recent (2008) and does not have the GPIB but the RS232 ..... :-//

All 34401A have the GPIB and the RS232 interface, this was standard from the beginning to the last model.
I have never seen a 34401A without GPIB, since this is part of the main PCB

Like Zucca said, I would hook up a remote control and see is the instrument reacts to remote commands

The change between the rectangular and the round button units was just a facelift. There is a service note which contains the numbers of the housing parts to convert an unit from the old design to the new design. All interior parts stayed the same.
So as HighVoltage pointed out your unit should have a GPIB connector (maybe covered by a dust cap) ;)
Title: Re: AGILENT 34401A
Post by: macboy on November 27, 2018, 06:33:34 pm
GPIB or RS232 both use the same command set. It's just a different connection.
Title: Re: AGILENT 34401A
Post by: lionelkjh on December 16, 2018, 01:14:05 pm
Bonjour; si le microprocesseur en face avant est mort (N80C51BH) est t'il possible d'y mettre un equivalent comme le AT89S51 (plus facile a programmer et reprogrammer que celui d'origine, et non doté d'un mask rom)????
Title: Re: AGILENT 34401A
Post by: lionelkjh on December 16, 2018, 01:15:23 pm
Hello; if the microprocessor on the front panel is dead (N80C51BH) is it possible to put an equivalent like the AT89S51 (easier to program and reprogram than the original one, and not with a ROM mask) ??? ?
Title: Re: AGILENT 34401A
Post by: coromonadalix on December 16, 2018, 02:27:31 pm
Original chip: Intel N80C51BH, package PLCC44

Other text on chip: 34401-88813 REV 2.0

AT89C51 is suitable replacement.

Here's an cpu dump attached i have found,  Taken from here : https://www.eevblog.com/forum/repair/hp-34401a-repair/ (https://www.eevblog.com/forum/repair/hp-34401a-repair/)


In French : le cpu est remplacable par un AT89C51
Voici un dump du cpu que j'ai trouver venant de ce thread:  https://www.eevblog.com/forum/repair/hp-34401a-repair/ (https://www.eevblog.com/forum/repair/hp-34401a-repair/)



Title: Re: AGILENT 34401A
Post by: lionelkjh on March 05, 2019, 04:36:30 pm
Hello everyone! I did not advance much on the failure of my multimeter. I was able to desolder the lcd display on the front panel, to perform some tests using the manual. All voltages are correct. I did not find anything abnormal. The different signals should be used with the oscilloscope around the microprocessor. But how to go back to the breakdown ??? Thank you for your advice (here is the front panel removed) |O
Title: Re: AGILENT 34401A
Post by: EE-digger on March 06, 2019, 04:06:17 am
I had a VERY similar problem on a 33120A function generator.  I have no idea if the two have any similarity but your symptoms give me deja-vu.

On the 33120A, a small reset chip was not coming up to full logic high output.  It was stuck midway up, hence resets were not clean for both the main and display processors.

I don't know if the 34401A actually has a separate display processor or not.
Title: Re: AGILENT 34401A
Post by: wictor on March 06, 2019, 11:15:29 am
There is separate processor in front panel. It's getting all display data from main board cpu. If there is no data arriving to front panel, there is nothing displayed.
Title: Re: AGILENT 34401A
Post by: coromonadalix on March 06, 2019, 11:26:19 am
the best course would be to have another display to do some tests,  or a logic sniffer  ...... to be sure

I wont argue with all voltages, but do a recheck, theres many of them

Its an old meter,  in mine i have done the recapping  to be sure, they where all working before, but the tantalums where ginving me frills, in one they where slightly brown"ish"
Title: Re: AGILENT 34401A
Post by: SpencerTC on March 06, 2019, 04:34:52 pm
Have you tried to get any response through GPIB (or other external communications)?
Title: Re: AGILENT 34401A
Post by: coromonadalix on March 06, 2019, 05:53:45 pm
With no screen   how can we know the gpib adress ?  unless you see it briefly ???
Title: Re: AGILENT 34401A
Post by: HighVoltage on March 06, 2019, 06:21:33 pm
With no screen   how can we know the gpib adress ?  unless you see it briefly ???
You just try them all, there are not too many possibilities.
Title: Re: AGILENT 34401A
Post by: picburner on March 06, 2019, 06:56:13 pm
With NI MAX you can do an automatic scan and it tells you which instruments are connected and their address.
I think you can do the same with Agilent's software.
Title: Re: AGILENT 34401A
Post by: HighVoltage on March 06, 2019, 07:56:21 pm
Yes, the Keysight software scans automatically for what is hooked up to any of the GPIB ports.
Title: Re: AGILENT 34401A
Post by: lionelkjh on March 10, 2019, 05:31:47 pm
Good evening; I made no attempt with the GPIB (because I do not have this big connector, nor software, nor interface!): in summary; I'm a little lost! I specify that this version and 2008 it is more recent than the first models released in the 90s. How to ??? :palm: :palm: :palm:
Title: Re: AGILENT 34401A
Post by: SpencerTC on March 11, 2019, 02:33:08 am
Well, the first thing I generally check with nonfunctional equipment is the easiest things...external communication (GPIB, serial), ensuring voltages are correct (that 3.3VDC test point is close to 3.3V, same with any other voltages noted on silkscreen/in service manual), unseat and reseat any socketed IC's, see if there are any unpopulated {or populated} footprints that could be looked at (ex. JTAG, serial), sniff around with logic analyzer.

I own a 34401A, although I've never had an issue with it and have not had a reason to become familar with the troubleshooting process of it. If  you happen to have a second instrument that you can compare voltages, signals, and responses to, then it can make the whole process much easier/quicker.

Try what you can and let us know what you find and I'm sure some more people will try to help (either I or some of the much more knowledgeable people on this site)

Good luck!
Title: Re: AGILENT 34401A
Post by: coromonadalix on March 11, 2019, 02:47:14 am
just had a small problem with my second  34401  the white display connector would not "get up"  or stuck at "pressed position" not closing on the flex cable center pins  when i pushed it to do a verification  ???

Worth to check



@Lionelkjh  you can surely build the project  ar488 usb to gpib adapter for almost nothing, you can communicate thru serial console,   or even try with the rs232 if there is somthing going out of the meter
https://www.eevblog.com/forum/projects/ar488-arduino-based-gpib-adapter/ (https://www.eevblog.com/forum/projects/ar488-arduino-based-gpib-adapter/)



But for the rs232 normally you set the communication type with the meter menu .....  the talkback (you only read / see the meter readings / no interaction is possible, is done at adress 37 if i recall