FLUKE 8050A searching adjusting tip to set DC at 0000

[modemhead]

Re: FLUKE 8050A searching adjusting tip to set DC at 0000

It is a very simple charging scheme. With the power switch off, the LM317 provides about 140mA of charging current via R26. This is a reasonable trickle-charge rate for basic 1300mAH NiCd cells, and should bring up a flat pack overnight.

With the power switch on, the current is increased by another 100mA via R25, to power the meter and continue charging the battery at a slightly reduced rate. If I recall correctly, the meter uses about 150mA.

The charging LED is always illuminated when the power switch is off. It's basically just an indicator of mains power, it is not related to the charge state of the battery pack at all.

If you plan to get some new cells to put in your meter, resist the urge to use NiMH. I'm not a battery expert, but I understand that they do not tolerate the constant trickle-charge as well as NiCd.

[Kiriakos GR]

Re: FLUKE 8050A searching adjusting tip to set DC at 0000

You did send me a travel to the moon with out ticket.

The meter came with out batteries and clips, just the plastic covers of the batteries was attached.

The 8012A was not power up with low batteries, and assumed that the 8050A it can power up because is not a true (option 01).

Nor the Fluke schematic was helping, in my understanding the schematic was indicating that if there is an active mini inverter instead of the transformer, it would act to charge the batteries.

Any way, thanks for pushing my curiosity so to retest and find the truth,
regarding batteries I had to improvise with what ever I have available,
but it did worked.

Now as new owner of the (option 01) may I ask if the CHG LED turns off at a certain point ?

[modemhead]

Re: FLUKE 8050A searching adjusting tip to set DC at 0000

From your pictures, it appears that you do have the battery-powered version (option 01), except that the batteries have been removed. The small toroidal transformer, and also R26, do not exist in the AC-only model.

It is not good to run this meter without the batteries. The power supply consists of an LM317 configured as a constant-current source. The design depends on the batteries being there to regulate the voltage to near, or just above, the nominal 4.8V. Without the batteries, the voltage will rise much higher, and may cause problems.

[Kiriakos GR]

Re: FLUKE 8050A searching adjusting tip to set DC at 0000

Well I have just one 8050A but I have its one from every flavor .. LOL
I was had order the 8050A with the battery option, but this one came instead.
It turned as seller error, and I got back one small compensation, as it was expensive to ship it back.

On this design there is a 9 Ohm resistor which came burned out and I had to replace it with two in parallel due the fact that there is no such value available at the stores.

Since this first repair the meter was good for some time.
Well I would feel much better if I had a spare PCB for the LCD.
If you keep spares, drop me one PM regarding an cost estimation.

[modemhead]

Re: FLUKE 8050A searching adjusting tip to set DC at 0000

I have several 8050As, and that looks perfectly normal to me. The one I use on a regular basis stays powered up 24/7, usually on the 20V range, and it bobbles constantly between 0.000 and 0.001, even with the input shorted. I have found it to be very trustworthy in terms of accuracy.

[Kiriakos GR]

Re: FLUKE 8050A searching adjusting tip to set DC at 0000

Thanks for the tip modemhead.
Crossing the leads it does has an effect and I recorded the details.

200mV = -00.01
2V = + .0000
20V = - 0.001
200V = + 00.00
1000V = + 000.0

Now it looks that the differences are not significant to be called as damage,
but the 20V range definably differentiates it behavior in contrast with the other ranges.

[modemhead]

Re: FLUKE 8050A searching adjusting tip to set DC at 0000

If you short the input and it reads zero within about 1 count, I wouldn't worry about it. I also would not use the Rel function to attempt to null a residual reading, because there is no guarantee that any small offset is constant once a low-impedance voltage source has been applied to the inputs.

There is no zeroing adjustment that I know of in an 8050A. The A/D converter includes an auto-zeroing phase that stores any non-zero error offsets in the system on tantalum capacitors C8 and C33, and subtracts them from the reading during the de-integration phase. You can check those caps to be thorough.

[Kiriakos GR]

Recently I did a repair on my FLUKE 8050A bench top DMM.
I have all the available documentation and I did an complete calibration & adjustments.

Funny enough there is no info about zeroing out the display at DCV.
I get 2-3 additional counts at the last digit depending the range.

I can use REL if I need the most of it accuracy, but I was hopping for a repair tip, as it looks that this adjustment is totally undocumented.