Fluke 8808A Question

[timb]

I have a Tek DMM4020, which is literally a rebadged Fluke 8808A. It's an absolutely fantastic meter and is my bench workhorse.

The behavior you're describing is absolutely not correct. When you power it up, it should default to DCV Auto. In that mode it should auto-range 100% of the time without you having to do anything. (The only exception to this I've ever encountered is when I tried to measure 1000V when it was in auto mode. It caused the meter to lock up, which is the only time I've ever seen that happen.)

If I were you I'd return the unit. It sounds like there's an issue with the main MCU (an off the shelf MSP430) or the ADC.

If you do go this route, keep an eye out for the Tektronix 4020 when looking for a replacement. These sometimes go cheaper than the 8808A because people don't realize it's the same meter

[Lucky22]

Hi All,
This is Irish seller of this Fluke Multimeter.
I'm trying to find a solution for GAD.
Re: Manual - it was on the CD that was included with this meter
Re: 14-Days return policy. I'm a honest seller- Please now worries about that
You can test it even longer.
eBay and PayPal protect You for at least 3 months anyway.
I will cover all the return costs so there would be no cost for You at all.
I can offer partial refund too - to cover the repair cost - but let's find the problem first.
I had 6 these meters up for sale - Buyer from Germany and GAD reported simillar problems.
I invited German's buyer to join this forum to find a solution.

History of these meters.
They came from a company liquidation, from  a test room (working environment)
Company Profile: "Word class end-to-end wireless coverage & capacity solutions, manufacturing and repair services"
All the meters were set to 220V (including meter that I sent to GAD) but there is a switch at the back to change the voltage to 110V.
I bought many instruments from this company. Many instruments were customised especially for this company.
For example I had customised version of Kikusui TOS9201S Resistance Testers.
I'm checking other forums too, in another languages.
Will be back later...
Regards

[GAD]

I suggest the following tests.

1) Put the 8808A in the DC mV range.  Using the Fluke 175, measure the input impedance of the 8808A.
2) Put the 8808A in the DC 2V range.  Using the Fluke 175, measure the input impedance of the 8808A.
3) Repeat for the 20V, 200V and 750V range.
4) Report all 5 readings.

Your readings/results should match what is in the 8808A manual below with the Fluke 175 reporting 0L for the mV and 2V range (unless note 1).

Thanks for all of your input. It is appreciated.

Readings of input resistance:

1: 0L
2: 0L
3: 10.10M
4: 10.10M
5: 10.10M

[GAD]

Hi All,
This is Irish seller of this Fluke Multimeter.
I'm trying to find a solution for GAD.
Re: Manual - it was on the CD that was included with this meter
Re: 14-Days return policy. I'm a honest seller- Please now worries about that
You can test it even longer.
eBay and PayPal protect You for at least 3 months anyway.
I will cover all the return costs so there would be no cost for You at all.
I can offer partial refund too - to cover the repair cost - but let's find the problem first.
I had 6 these meters up for sale - Buyer from Germany and GAD reported simillar problems.
I invited German's buyer to join this forum to find a solution.

History of these meters.
They came from a company liquidation, from  a test room (working environment)
Company Profile: "Word class end-to-end wireless coverage & capacity solutions, manufacturing and repair services"
All the meters were set to 220V (including meter that I sent to GAD) but there is a switch at the back to change the voltage to 110V.
I bought many instruments from this company. Many instruments were customised especially for this company.
For example I had customised version of Kikusui TOS9201S Resistance Testers.
I'm checking other forums too, in another languages.
Will be back later...
Regards

Thanks for posting!

[GAD]

I have a Tek DMM4020, which is literally a rebadged Fluke 8808A. It's an absolutely fantastic meter and is my bench workhorse.

The behavior you're describing is absolutely not correct. When you power it up, it should default to DCV Auto. In that mode it should auto-range 100% of the time without you having to do anything. (The only exception to this I've ever encountered is when I tried to measure 1000V when it was in auto mode. It caused the meter to lock up, which is the only time I've ever seen that happen.)

If I were you I'd return the unit. It sounds like there's an issue with the main MCU (an off the shelf MSP430) or the ADC.

If you do go this route, keep an eye out for the Tektronix 4020 when looking for a replacement. These sometimes go cheaper than the 8808A because people don't realize it's the same meter

Thanks for posting. I have to say that I really do like the layout, functionality, and feel of this meter. I'd love to get it working right.

[ModemHead]

Sticky relays?  Give the board a few taps and see what happens.

[GAD]

Sticky relays?  Give the board a few taps and see what happens.

No change

[ManateeMafia]

 I used a DMMCheck Plus + handheld dmm and probed different components using the 10V range to see where the test signal went. It appears the signals go under the aluminum shields and I haven't been able to see where it pops back up. It would require me to remove the front panel and pcb to get them out of the way.

I attached a few photos with measurements of 5V at the inputs. I also included a couple photos of my bodge wire. If you get time, would you verify which of the two bridge rectifiers it should connect to?

[GAD]

I used a DMMCheck Plus + handheld dmm and probed different components using the 10V range to see where the test signal went. It appears the signals go under the aluminum shields and I haven't been able to see where it pops back up. It would require me to remove the front panel and pcb to get them out of the way.

I attached a few photos with measurements of 5V at the inputs. I also included a couple photos of my bodge wire. If you get time, would you verify which of the two bridge rectifiers it should connect to?

Thanks for the pics!

Re: your wire - as with all things in life that have a 50/50 chance, the right choice was the other one.   There is continuity on my meter between the linear voltage rectifier you have wired and the closer bridge rectifier on the closest pin (as you'd expect given the orientation, which is opposite).

FWIW I had the entire board out and could not figure out how to get the larger shield off.

Here are my voltage readings while measuring a 9V battery (9.17 at the terminals):

[ManateeMafia]

It looks like the 4.6V is normal, it isn't related to the input (tested w and w/o 5V).

I will poke around the board tomorrow and Sunday to see if we can get to the other side of the relays. I will also check and see if I can find any control signals for the them.

Thanks for the help with the wire.

[GAD]

I posted a thread in the Repair forum: https://www.eevblog.com/forum/repair/fluke-8808a-won't-auto-range/

[Towger]

Since the original owner was in the 'wireless' business.  Am I correct in thinking that feeding a reasonably powerful high frequency signal into a meter, even if the voltage is well below the rated maximum cause would damage the front end? Ie the max rated voltage drops as the frequency increases.

[retiredcaps]

Readings of input resistance:

1: 0L
2: 0L
3: 10.10M
4: 10.10M
5: 10.10M

Those readings are correct.