Author Topic: agilent HP 34401a insanely simple thoubleshooting and repair  (Read 1955 times)

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Offline ddavidebor

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agilent HP 34401a insanely simple thoubleshooting and repair
« on: February 17, 2013, 02:31:24 AM »
hello guys

it's my first post on this forum but i follow eevblog since 2 years ago.

my english is not good at all, expecially grammar. i think you should understand.

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so, let's speak about this meter

i thinks this is the most insanely simple throubleshooting i've ever ever made.

i've paid this meter about 150€ (200usd).

i've bought it broken with "err 621" "ac rms full scale failed" , but when i've done the auto-test this meter also wrote "err 622" "unable so sense frequency" or something like this, i don't remember.

receive 2 errors it's a great thigs! i've read the service manual and the only component used in all the two test is C301, the big white capacitor in the photos.

i've remove it and replaced it. none, now only err 621 again...

because the error are not the same, first 621, next 621-622 then 621 only again, i've thought "is a mechanical problem!"

so a bit on trouble later i've seen that the pcb trace that go to the cap has a very very very small damage. like a hair.

i've scaped the trace and placed a bit of solder.

and that's all, the most simple word repair! incredible...

now all test are "pass" yeahhhhhh
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and it has 35 calibration.... so about one every 4 months, amazing...


Offline MetraCollector

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Re: agilent HP 34401a insanely simple thoubleshooting and repair
« Reply #1 on: February 17, 2013, 03:38:17 AM »
Gratulation, you are lucky ! :)
I bought 34401A 3-4weeks ago and cost me 350€, but fully functional.

It seems to be a repairable machine except the ASICs used. :)

Regards Ondrej

Offline ddavidebor

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Re: agilent HP 34401a insanely simple thoubleshooting and repair
« Reply #2 on: February 17, 2013, 03:54:10 AM »
yes, it has 160+ pages of service manual, and a lots of schematics and layout

the internal quality is incredible. after 10+ years, all the components are in perfect condition and the solder attach it very well, it's a pleasure to repair this things....

i think now i will sell it at 350€  ;D and buy a fluke 87...

but the limit test is amazing  :scared:

Offline T4P

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Re: agilent HP 34401a insanely simple thoubleshooting and repair
« Reply #3 on: February 17, 2013, 04:34:42 AM »
Why would you trade up a 34401a for a 87V?  ;)
http://the4thpin.comeze.com <-- Rants and Reviews! sorry my english  :palm:

Offline AndyC_772

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Re: agilent HP 34401a insanely simple thoubleshooting and repair
« Reply #4 on: February 17, 2013, 04:45:47 AM »
I wouldn't. I use the Keithley 2000 on my bench a lot more than the Fluke 289 that usually sits unused in a cupboard. Usually the Fluke only comes out if I need to measure capacitance or data log something.

Offline ddavidebor

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Re: agilent HP 34401a insanely simple thoubleshooting and repair
« Reply #5 on: February 17, 2013, 06:12:10 AM »
Why would you trade up a 34401a for a 87V?  ;)

oh but there's a lot of money difference  O0

in fact, i don't need a 6.5 multimeter with datalog, 4 wire ohm... and all the function it has... i alredy "have" it in school so the 3-4 times in a year i need it i can use a school one.

i think 34401a will miss me...  :'(

i'm veri happy with my minipa et-997 cheap 30€, i only need faster continuity and better diode voltage drop. (et-997 stop to 2.5v, i need >3v )
in fact, also this agilent can't measure led voltage drop...


Offline chickenHeadKnob

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Re: agilent HP 34401a insanely simple thoubleshooting and repair
« Reply #6 on: February 17, 2013, 06:46:43 AM »

I am like andyC, I much prefer bench meters when sitting at the bench, only use handheld if forced. The real puzzle here is why or how did the trace go bad. Leaky electrolytics - that would be  common to anything and obvious.

Offline ddavidebor

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Re: agilent HP 34401a insanely simple thoubleshooting and repair
« Reply #7 on: February 17, 2013, 06:58:53 AM »
i think it was a very non-repeateable defect. it was tiny tiny tiny tiny...

maybe, when someone was repairing it for another things hurt the cap, or maybe someone scratch it with a screwdriver trying to doing something else. i don't think the cap was an electrolytic one... do you know what tipe is? i think plastic film maybe, i don't know...


someone found a tantalium cap shorted with the same error "err 621". i had check it is working.

i also like a lot bench meter. they are solid, no battery, you can insert banana jack with only one finger, bright scree... and because a bench meter is always in the same position, you can use it without watch where you push.
oh, and 4.5 digit mode is incredible fast!

but, in fact, i don't have space for it

Offline ddavidebor

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agilent HP 34401a insanely simple thoubleshooting and repair
« Reply #8 on: February 21, 2013, 12:07:46 AM »
I've check it against a 2 yo meter.

The difference is under the maximun day drift for  both ac and dc, half a month for 4w resistance and current, identical for diode. Spot on on frequency and period also.

in conclusion, spot on!


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