[volt-nuts] Fluke 5205a Repair

Chuck Harris cfharris at erols.com
Mon Sep 28 16:41:40 EDT 2015

Hi David,

Do be careful inside of that 5205A, it has lots of gotcha
points that would be quite happy to light you up like a
Christmas tree.

Mine has some issues with the fault circuitry from time-to-time,
particularly after it has sat for a while.  I believe that most of
the problem is related to intermittent short circuits on some
circuit, or other, tripping the fault circuitry.  I have made no
attempt, as yet, to hunt them down.

Try giving your unit a hard thump on the bench, and blowing it out
with compressed air.  I found that mine got over its problems for
quite awhile that way.  How long?  I don't guess I will know until
the next time it faults.

I think it is probably either a stray spider building a web in the
wrong place, or tin whiskers.

-Chuck Harris

David Garrido wrote:
> 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,
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