If it's not too much of an inconvinance, I would appreciate more info regarding the mod you spoke of. I don't mind the wait as I'm also away for the holidays.
Hey, anyone have a spare LCD from one of these?
Modemhead,
If it's not too much of an inconvinance, I would appreciate more info regarding the mod you spoke of. I don't mind the wait as I'm also away for the holidays.
I should be able to make the mod just by looking at the datasheet of the lm317 and the schematic of the 8050A, but you can't go wrong with having more information.
Thank you,
Phil
This is not a bad alternative to sourcing a replacement LCD display for a Fluke 8050A DMM.
<snip>
http://lous.home.xs4all.nl/fluke/Fluke8050Asite.html
The 8050A LCD does suffer from low contrast.
Richard
ModemHead,
Great description. Thank you very much. I will do this mod soon.
But before I do, without knowing anything else, do you think the batteries is causing the DMM to not function properly? I had it plugged in for a couple of hours when I first got home and switched the thing on. It worked at that point, but the low battery indicator on the LCD was always on. Then I noticed last night that it worked for a bit and then when I switched it off and back on again, I would get the low battery indicator on the LCD again along with a "1" and then the LCD would fade out. After switching the thing on and off again several times and sweeping through different ranges and voltage/resistor setting, the same result would occur. All of this after the DMM has been plugged in for the past 48 hours.
Well thanks again and I really appreciation the tutorial you provided. Hopefully this will get my DMM running again and consistently this time.
You're welcome, happy modding/repairing.
Your problem sounds exactly like a dead battery pack. Bad cells will pull the voltage on this 5V nominal supply down far enough that the meter will not operate, or won't operate for long.
An alternate, even easier fix, is just to solder in any working sub-C NiCd cells that you have. If you're not concerned about actual battery operation, four 1.2V cells of just about any size will allow the meter to work fine on AC power. Until the cells go bad, as they all do. Smaller cells may get warm on the 140mA constant trickle...
This is not a bad alternative to sourcing a replacement LCD display for a Fluke 8050A DMM.
<snip>
http://lous.home.xs4all.nl/fluke/Fluke8050Asite.html
The 8050A LCD does suffer from low contrast.
RichardI've done that one too, but the back side of that LED display is a labor of love. Eh, some people climb rocks for the heck of it, I play with old gear.
I don't have any C NiCd cells so I'll just stick with the mod you provided. Thanks again for all your help. I'll post my results in a day or two.
Since the transformer and regulator are energized as soon as you plug the meter in, 5.5V or so should appear across U26P2 to C23-negative even before turning the power switch on. You can check your work this way without possibly damaging the rest of the meter if you make any mistakes.
I am having an issue with the mod. I performed the steps that you listed, although my PCB was slightly different than the picture provided. When cutting the trace that connects to U26.1, I had multiple traces (3) ending at U26.1 besides the battery pack. These multiple connections was the transformer, T3, C22, and C34. The cut disconnected those components from U26.1. I take it this is correct, no?
Also, after adding the 510 ohm resistor from C23 (negative pin) to U26.1 and plugged in the power cord (after all other steps were performed), I only got a voltage of 4.5V when probing U26.1 and C23 (negative pin), so I ended up upping the resistance to ~650ish ohms to get 5.5V. At this point, I turned it on and nothing appeared on the LCD.
I checked my work a few times and I'm fairly certain I did the steps correctly. When I checked the voltages at TP2, 3, 4, and 5, I don't get the voltages as described in the schematic. I was checking these voltages when having one probe placed on C23 (negative pin) and the other on the test points. The voltages observed were roughly 6V (6.5V on some). But then I thought that I may be placing my other probe, (that connects to C23 negative pin) incorrectly so I placed in on the front panel common plug and the voltages on the test points were in the mV range.