FLUKE 8050A searching adjusting tip to set DC at 0000

[Kiriakos GR]

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

I am glad too with these good news, and I do smoke two packages of cigarets daily.

The problem is not the smell of the cigaret but it could be the type of business which this meter was working before you get it (environmental pollution by fumes coming from dangerous chemicals).

Either way the PCB decontamination it is suggested by Fluke too, especially when new soldering could cause an excessive amount on soldering paste over the bare PCB.

I have a small (hard) copper brush which I use in combination with Isopropyl alcohol so to remove any sign of soldering paste (baked & dry) with 100% success.

[Totoro]

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

Hello Kiriakos,
You're right, it doesn't make much sense. So, I thought I would find the temperature sensitive part. I heated up a metal rod and went around touching stuff. Some little changes but what I would expect. You suggested cleaning the board. Yeah, right, I thought. That's going to make a difference. The board looks really clean.
Anyway, I grabbed the isopropyl, a brush and some paper towels and started cleaning the underside of the board. Immediately, I smelled the stink of old cigarettes. I hadn't noticed anything before. And...
It works now! OK, not yet perfectly but crap on the board is definitely the problem. I will do a more thorough cleaning, component side, switches etc., but I wanted to reply and thank you for pointing me in that direction. (My guess is that it was the moisture in my breath and not the temperature that made it change so much. I saw in the service manual a mention about cleaning but kind of ignored it. It must be there for a reason.)
So, a warning to all you smokers out there, it kills equipment, too.
And thanks again Kiriakos!

[Kiriakos GR]

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

You last report does not make sense, but you better wash the entire PCB with Isopropyl alcohol, if there is any contamination this will cure it.

[Totoro]

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

Well, I had a chance to look more into this and I found that the 20V range is VERY temp sensitive. Even blowing on the circuit board will change the offset from -30mV to -100 or even more. I am really confused by this.
What is different with the 20V range? I will try to add more as I try to investigate further...

[Totoro]

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

The resistor divider network is OK. I have gone over that very carefully. I have even measured higher voltages and accounting for the offset they are accurate.
Your idea about the switches is a good one. I will definitely check that! (I will be busy with other things for the next couple of days and will not be able to do very soon. :-( )
I really like keeping this old equipment alive. I am determined to find what is the problem here.
Thanks for your help and interest!

[Kiriakos GR]

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

Well if this does not cure it, there is other two issues that I can think.
a) range switch problem in the specific range.
b) resistors network needs re soldering or it is damaged.

[Totoro]

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

Hello Kiriakos,
Thanks for the reply. I think you mean C8 and C33. I thought about these, too, since in the documentation it says they store offset voltages to the integrator and comparator. The thing is, the A/D circuitry obviously works because the 200mV and 2V ranges are fine. But, if I can't find anything else I may have to swap these out and see if anything changes.
Thanks again!

[Kiriakos GR]

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

Responsible for fluctuation I have read that is possible to be two tantalum capacitors that they are located at about the end of the range switches near to the center area of the PCB.

[Totoro]

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

Hello all,
I found this thread (and site) because a search led me here. The problem here is not exactly what I have but kinda close. Maybe someone can help lead me to a solution. Thanks!
I also have a Fluke 8050A-01 and it works fine except that the 20V and higher ranges have a negative voltage offset. I got this off eBay and expected to have to put new batteries in. I swapped out the dead Panasonic NiCDs (already a replacement) and used NiMH units. (I know that constant trickle charging can kill NiMH so I simply won't do that.) I let the batteries charge and was pleasantly surprised by a working meter with a nice contrasty display. But...
The 200mV and 2V ranges are fine (and so then the ohm and current ranges). But the 20V range sits at about -30mV (30 counts) with shorted input. And it can vary, sometimes as low as -10mV and sometimes much higher, even -100mV! The 200V range tracks with a 3 count offset and so on. Again, the 200mV and 2V ranges are fine and give correct values for test voltages, +, -, AC. So, I assume the A/D is OK.

I've probed all around and cannot figure out where the voltage is coming from. The voltage is zero right up to the A/D (R8).
A bit more info in case it helps. The +13V rail is rather low at about 9.8V. Other voltages are in line. I have replaced all of the power supply caps (Frolyt ERF series) but the voltages and symptoms are unchanged.

If anyone has any ideas, I would really appreciate it. Thanks to all in advance.

[budm]

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

Glad you found the cause of the failure.

[Kiriakos GR]

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

just a broken pin.

At the point where the pin was broken it was in a totally blind spot, and impossible to see with out extraction.

Always with a bit of motivation I am getting more productive.
Thanks mate.


Even Fluke have seen that on me.
http://www.ittsb.eu/forum/index.php?topic=518.0

[budm]

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

Base on you voltage reading, the Vin-Vout = 9.1 - 3.8 = 5.3V (Notes: right now your batteries voltage do not reach the full charge yet since you are only seeing 3.8V), so the power dissipation is about 5.3 x 0.14 = 0.74 Watt which is not too bad, it should get cooler as the batteries are at full charge, but when the power switch is on, then it will draw more current and heat up more.

It looks like the metal tab dissipates better heat than the plastic tab. I think you will be OK with the old one, it did not get damaged, just a broken pin.
At 50~60c. I do not believe the Jct of the LM will be @150c.

[Kiriakos GR]

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

I did play my last card on this game and soldered the old back.
Volts 2.65V / 3.9V / 10.13 temp 51C it runs far cooler than with the other one.
I am going to measure charging mA and be back.

98 / 136mA

It looks that today 9 June, this meter restored back 100% after all this research, thanks budm !! .

[budm]

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

The LM317 has Thermal protection, 64C with that heatsink? At worst, the LM317 will shutdown, I think it will get even hotter when the case is put back together, you may have to get the TO-220 with metal tab instead. It also makes sense why the resistor get hot since if the ADJ pin is not connected, the LM317 will just let the current flow right through (with slight voltage drop across the LM IN/OUT) and the current is only limited by that 9.1 Ohms resistor.

[Kiriakos GR]

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

Temperature by K-Type thermocouple gets high up to 64C

There is heatsink on it.
About the old one I do not know if it works.

[budm]

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

Per your picture, measure at the Middle pin (Out) and the Right pin (output pin). At least you are getting the correct current reading now. Can you fix the broken pin by extending it with wire?

[budm]

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

I believe the input voltage to the LM317 is about 18VDC, that means if the batteries is at 4.8V, the voltage across the LM317 will be about 13.2V, so at 140ma, the powe dissipation will be about 13.2 x0.140 = 1.85 Watts, which will be quite hot, and will be hotter when power switch is turns on. I put heatsink on my LM317 for the 125mA current source for charging my 4.8V NiCad using 19Vdc power source.

[Kiriakos GR]

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

As is the LM in the picture from left to right 2.6V / 3.8V / 9.1V as negative point I used the batteries negative.

[budm]

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

What voltage do you get if you put meter at the input pin and the output pin, then we can determine the power dissipation of the LM? Just multiply the voltage reading by 140mA to get the power. LM317P is the plastic tab without the metal tab for heat dissipation?

[Kiriakos GR]

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

Unbelievable ... the LM which the meter was have on it, found to have one lead broken.

But now those resistors does not get hot any more and the charging current is at 100mA and 140mA with the switch off, but the LM317 runs hot 45C

The old one was LM317MP (attachment) and the New one LM317P+.