[volt-nuts] Fluke 5205a Repair

[David Garrido]

Hello All,

I know this is not specifically discussing precise voltage, but it is about producing it.  We should consider starting a FLUKE calibration equipment repair forum.

Anyhoo………I have been scratching my head over this 5205a issue for a couple weeks now.  It presents with a OVERLOAD light after the warm-up period of about 30 seconds. If I try to apply a voltage from the 5200a I get a FAULT light and I have to reboot the power in order to clear the FAULT led, but the OVERLOAD led still comes back on after the warm-up period.

Going through the TS procedures on page 4-24 in the manual tell me to check for an issue “…….in the disabling circuit between the Warm-Up Delay circuit and U8-11 on the logic assy.”

The first place I looked was at both of the bases of Q104 for a difference of more than 125mV. Pin 2 reads -5.83v and pin 5 reads -5.19v, so obviously it sends it into OVERLOAD mode.

Knowing this, I continued deeper into the circuit.  I am currently working in the Neg HV Sensor circuit on pg. 3-7 and it tells me “If the output (HV) becomes less negative than -2225a, a high output results at the coupler U52, setting the instrument to standby.”  Pin 3 of U167 is +4.97v, Pin 2 is +6.25v, Pin 7 is +21.1v and so is Pin 5 of U52.

Now, there are two adjustments in the cal procedure, 4-82 & 4-85, that adjust the POS and NEG Current Trip Level, but I am not certain I want to disable the OVERLOAD circuit to make this adjustment without knowing what may be wrong for fear of doing more harm than good.  But on the other hand, this may very well be exactly what is causing the tripping in the first place.

I could use any help one would offer and the manual is located here:

http://assets.fluke.com/manuals/5205A___imeng0000.pdf <http://assets.fluke.com/manuals/5205A___imeng0000.pdf>

Cheers,

David