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

• Agilent 34401A Errors 612/613, 615 and 617-619
  Posted by Ole on 09 Jun, 2022 10:05
• 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
• #1 Reply
  Posted by strawberry on 09 Jun, 2022 10:22
• Q202 Q211
• #2 Reply
  Posted by Kleinstein on 09 Jun, 2022 10:26
• 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.
• #3 Reply
  Posted by HighVoltage on 09 Jun, 2022 10:26
• 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
   
• #4 Reply
  Posted by Ole on 09 Jun, 2022 11:31
• Quote

  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
  
• #5 Reply
  Posted by HighVoltage on 09 Jun, 2022 12:10
• The big capacitors on these instruments usually never go bad.
  But make sure to test all rail voltages and ripple on them.
  
• #6 Reply
  Posted by Ole on 09 Jun, 2022 13:05
• 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?
• #7 Reply
  Posted by bdunham7 on 09 Jun, 2022 13:39
• 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.
• #8 Reply
  Posted by Dr. Frank on 09 Jun, 2022 15:02
• 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
• #9 Reply
  Posted by Ole on 09 Jun, 2022 15:32
• 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.
• #10 Reply
  Posted by strawberry on 09 Jun, 2022 17:58
• could check first with multimeter if it is blown or not