Agilent 34401A Errors 612/613, 615 and 617-619 - Page 1
Forum section: electronics / repair

author: Olivia
author_rank: Regular Contributor
timestamp: June 09, 2022, 10:05:14 am
content: I have bought a used 34401A.The Basic Rundown:-Voltage Measurements via Input is working-Current Measurement is Working-Front Connectors have been used-Ohms Measurement does not work-Meter is from 2006 with 0609 on LM399-Big Electrolytics seemed fine for a smoke testThe Selftest gives the following Errors:612: Ohms 500 nA source failed613: Ohms 5 uA source failed615: Ohms 10 uA source failed617: Ohms 100 uA source failed618: DC high voltage attenuator failed619: Ohms 1 mA source failedI have not yet desoldered any components

author: strawberry
author_rank: Super Contributor
timestamp: June 09, 2022, 10:22:34 am
content: Q202 Q211

author: Kleinstein
author_rank: Super Contributor
timestamp: June 09, 2022, 10:26:09 am
content: The 2 JFETs from the ohms part are prime canditates to check.The error 618 about the divider may also be caused by the ohms current source not working. So I would fix the ohms part first and this may also fix this error.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 09, 2022, 10:26:46 am
content: Also, use the search function, we have discussed these errors a few times and you can learn lots from these posts. Like this onehttps://www.eevblog.com/forum/repair/agilent-34401a-error-606/msg934953/#msg934953

author: Olivia
author_rank: Regular Contributor
timestamp: June 09, 2022, 11:31:32 am
content: QuoteLuckily those are TO-92s so I can desolder them easily.I dont have the full parts list on hand, so I might need some help for finding the replacement parts.Q202: [1671 (8)08] is written on that one. Not sure about the first eight in the second blockQ211: [BF47 PN 4117A] not 100% sure might be a simple 2N4117A.The big Elkos in mine are all:a) good lookingb) non bulgingc) covered with a piece of kapton (?) tape on topC752: 4700u 25V 105°CC556: 2200u 25V 105°CC553: 1000u 50V 105°CC551: 1000u 50V 105°C

author: HighVoltage
author_rank: Super Contributor
timestamp: June 09, 2022, 12:10:47 pm
content: The big capacitors on these instruments usually never go bad.But make sure to test all rail voltages and ripple on them.

author: Olivia
author_rank: Regular Contributor
timestamp: June 09, 2022, 01:05:03 pm
content: Well, if those Caps didnt look like freshly soldered in I would have switched them for fresh ones before giving the instrument a smoke test. Now only one question remains: What kind of JFET´s are Q202 and Q211?

author: bdunham7
author_rank: Super Contributor
timestamp: June 09, 2022, 01:39:57 pm
content: These are TO-92? According to the Agilent manual and my recollection, I thought they were SMD. In any case, if they are TO-92:Q211 is a PN4117A and is generally in stock at places like Mouser.Q202 is a selected 2N5461. I do not know the selection criteria, but the basic 2N5461 is still available from Jameco, although it is listed as obsolete/unavailable elsewhere.

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 09, 2022, 03:02:14 pm
content: Hello Ole,that's a common problem, better see this link:https://www.eevblog.com/forum/repair/hp-34401a-error-612-613-615-617-618-619-621/75/In most cases it's U201, an AD706, or it's a relay.First, check the values of driving currents when in 4W Ohm.Frank

author: Olivia
author_rank: Regular Contributor
timestamp: June 09, 2022, 03:32:33 pm
content: Q211 i will order a few replacement PN4117A from Mouser and as for the Q202, the 2N5461 is availible for cheap at a online shop, alternatively I thought about purchasing a few J176/J177 P-Channel-JFETs and replacing the Q202 with one of those.

author: strawberry
author_rank: Super Contributor
timestamp: June 09, 2022, 05:58:35 pm
content: could check first with multimeter if it is blown or not