Fluke 85 Repair (Strange 10x voltage)

[Spekham2013]

Hi everyone,

I recently acquired a old broken fluke 85 with the service manual. All the ranges work perfectly fine except for the voltage ranges (mV works normal). When reading a voltage I quickly get a overflow and it takes a long time to go to zero. It is as if a capacitor is really slowly discharging. When I read a small voltage (0.3 volt) the multimeter shows a voltage of exactly 10x higher. When going up a range this becomes 100x. I know the multimeter IC will probably not be fault because the mV range still works like normal just like all the other ranges. Has anyone seen a problem like this before and if so can you point me in the right direction?

[dacman]

First, try cleaning the switch and use a lubricant on it.

[retiredcaps]

1. Clear focused pictures of the inside PCB helps us help you.

2. If you measure a 9V battery, what does the lcd do and show?

3. When you short the probes, what does it show on DCV?

4. Do you have another working meter to take measurements?

[mzacharias]

Also check the input impedance (resistance) using another multimeter.

These sometimes get bad input jack assemblies.

[Spekham2013]

1. Added pictures

2. The multimeter goes into Overload

3. Goes down to 0v not instant though it does go fast

4. Yes I have two more working multimeters. (one Prema 5000 and one crappy multimeter)

I have also tried to measure input impedance. Only for the mV range could I get a reasonable reading (10.8 MOhm). For the voltage ac/dc range the meter world overflow. I cleaned the input jacks with same kontakt cleaner.

[Pete66]

Its probably your rotary switch.
Remove it as described here and clean board underneath with IPA and toothbrush
http://mrmodemhead.com/blog/fluke-83-dmm-repair/

[Spekham2013]

Its probably your rotary switch.
Remove it as described here and clean board underneath with IPA and toothbrush
http://mrmodemhead.com/blog/fluke-83-dmm-repair/

I tried this but it doesn't change anything.

[coromonadalix]

hows the dial pins are, are they physically okay or they are worn out

I have 83 (first series) at my job who does pretty funny stuff, they even beep when off  loll,  a good cleaen up and i did add more tension on the dial contacts by bending them a little more to add some pressure ??

The 83 are heavily used at my job, and their life are about to end when were gonna buy new ones, im waiting for the eevblog 150$ meter  ...

[Spekham2013]

hows the dial pins are, are they physically okay or they are worn out

I have 83 (first series) at my job who does pretty funny stuff, they even beep when off  loll,  a good cleaen up and i did add more tension on the dial contacts by bending them a little more to add some pressure ??

The 83 are heavily used at my job, and their life are about to end when were gonna buy new ones, im waiting for the eevblog 150$ meter  ...

Took the dial out and cleaned it. Looks fine little bit of wear and tear. The problem still persists. Any more idea's?

[mzacharias]

This pretty much proves your input jack assembly is bad. Take the main board out, plug a known good set of test probes into the main AC/DC input jacks and simply use another meter to measure from each probe tip to the appropriate points on the underside of each input jack. You'll  find the bad one pretty quick.
Replacements are available on eBay and other sources as well; they run in the 20-30 US dollar range.



"I have also tried to measure input impedance. Only for the mV range could I get a reasonable reading (10.8 MOhm). For the voltage ac/dc range the meter world overflow. I cleaned the input jacks with same kontakt cleaner."

[coromonadalix]

Do they have a good pressure ?

[retiredcaps]

What does measuring a 1k ohm resistor show?  What does the meter show when you short the probes when it's on ohms setting?

[Lifeborne]

Check Z1 values, if they are good then it may be the internal MCU switches that are faulty. Check a voltage in all the manual ranges.