Agilent 34401A Errors 612/613, 615 and 617-619

[Ole]

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 test

The Selftest gives the following Errors:
612: Ohms 500 nA source failed
613: Ohms 5 uA source failed
615: Ohms 10 uA source failed
617: Ohms 100 uA source failed
618: DC high voltage attenuator failed
619: Ohms 1 mA source failed

I have not yet desoldered any components

[strawberry]

Q202 Q211

[Kleinstein]

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.

[HighVoltage]

Also, use the search function, we have discussed these errors a few times and you can learn lots from these posts. Like this one

https://www.eevblog.com/forum/repair/agilent-34401a-error-606/msg934953/#msg934953
 

[Ole]

Q202 Q211

Luckily 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 block
Q211: [BF47  PN  4117A] not 100% sure might be a simple 2N4117A.

The big Elkos in mine are all:
a) good looking
b) non bulging
c) covered with a piece of kapton (?) tape on top

C752: 4700u 25V 105°C
C556: 2200u 25V 105°C
C553: 1000u 50V 105°C
C551: 1000u 50V 105°C

[HighVoltage]

The big capacitors on these instruments usually never go bad.
But make sure to test all rail voltages and ripple on them.

[Ole]

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?

[bdunham7]

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.

[Dr. Frank]

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

[Ole]

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.

[strawberry]

could check first with multimeter if it is blown or not