FLUKE 8050A searching adjusting tip to set DC at 0000

[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 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

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

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!

[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...

[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

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

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.