Author Topic: Fluke 8800a - Ohm PCB fault?  (Read 895 times)

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Offline SimoSTopic starter

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Fluke 8800a - Ohm PCB fault?
« on: August 16, 2018, 09:49:49 pm »
Hello everybody. My first time in this forum, I appreciate the level of discussion and the competence of many people.
I recently started to work around tube amplifier and set-up a small laboratory, really as a beginner.
I found a Fluke 8800a in a local website of old stuff and bought it for few euros.
It worked good for AC/DC measurments, but not for Ohms.

I open it, cleaned, substituted batteries on the Ohm PCB (2xAA - the previous ones had a leakage so it was a dirty job).
All the ohm measures are now greater than real. In example a 1.2MOhn resistor is 6MOhm if measured with 20MOhm scale, or 1.6MOhm if measured with the 2000kOhm scale. During time (hours) the measures on the display decrease gradually.
I tested all the power levels indicated in the manual on the main board and they are correct.
I tested the Ohm PCB with 1Ohm resistor, and the voltage drop 1mV as indicated in the manual.
I check the power supply by the batteries all around the Ohm PCB and it's a nice 3.2Vdc.

Any suggestion? Iknow it's an old device, but quite accurate on the VAC/VDC part and an opportunity for me to learn something new.
Thanks in advance for your help.
 

Offline lowimpedance

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Re: Fluke 8800a - Ohm PCB fault?
« Reply #1 on: August 16, 2018, 11:23:28 pm »
Make sure you have 'really ' cleaned the ohms assembly and carefully the main PCB where the ohms assembly plugs in,  as any residue from the leaking batteries could easily upset the very high impedance's  in these areas, (who ever thought batteries in a bench meter was a good idea should be  :horse:) . Also as well as a good cleaning check for any corrosion damage to tracks and bad solder joints, does gentle flexing of the PCB change the reading in any way.
 
Incidentally the 8810a  model revised the ohms to a proper isolated supply to eliminate the dumb battery idea. But it was an optional extra as was the other plug is cards (AC, and I/O) so the basic meter was only DC volts until you coughed up more cash  :(. So be careful if you find an 8810 for a good price that you check what options if any have been installed.
« Last Edit: August 16, 2018, 11:28:17 pm by lowimpedance »
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 


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