| Electronics > Repair |
| Fluke 87-I repair |
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| retiredcaps:
Just a couple of other measurement suggestions? 1) What is the resistance between Z1 pin 1 and the left side of R29? Mine is 0.2 ohms. I'm curious if the pcb track is damaged? 2) What is the resistance of R2 out of circuit? |
| staze:
I got the back switch all clean... I don't see anything dirty anymore (there wasn't really before). I'll just have to dunk the whole thing again tomorrow (once I pick up another bottle of 99% IPA) and let it soak a bit. But from what I see in the description for the 83, it sounds like when the switch is off, it's just shorting Vss to ground... so shouldn't there be SOME draw when off (only 9uA, or about 1/100th of what it draws when on). That said, Vss and Vdd appear to be out of spec when the unit is on... which is probably due to whatever has failed. But I really don't know at this point. |
| retiredcaps:
--- Quote from: staze on February 20, 2014, 06:24:03 am ---I'll just have to dunk the whole thing again tomorrow (once I pick up another bottle of 99% IPA) and let it soak a bit. --- End quote --- A bit of a long shot, but I also take a sharp multimeter probe or dental pick and carefully drag it between the pins of the main IC during the IPA bath. The alternative is to use a stiff toothbrush and give the pins a good scrub. After it dries thoroughly, I then inspect it with a 10x jewelers loupe. Right now, I'm out of ideas, but if you are taking voltage readings, please post them so we can see. |
| staze:
--- Quote from: retiredcaps on February 20, 2014, 06:07:45 am ---Just a couple of other measurement suggestions? 1) What is the resistance between Z1 pin 1 and the left side of R29? Mine is 0.2 ohms. I'm curious if the pcb track is damaged? 2) What is the resistance of R2 out of circuit? --- End quote --- 1. 0.03R after zero'ing out the leads/probes. 2. 850K. Damn. Means I have to find a replacement. Gar. So just tested Vss and Vdd again. Vss is perfect at -3.20V. Vdd is at 2.99V. So, Those are dandy. So it's not power supply, seemingly. Vref checks out at 1.2324V. VBT+ is 3.5948, VBT- is -5.794V. So I think all the various PS measurements are right on. My leakage is somewhere else, it would seem. Doing the calculation, to get only 9.805uA of leakage (on a brand new, 9V battery at 9.473V) there's a good >1Mohm resistance the battery is being shorted through... |
| staze:
Scrubbed... nothing, no change. And all the pins look good. If you have the unit apart, could you tell me what R61 measures as (in circuit)? I ask because the reflow process for this meter and that resistor appears to have gone wonky, since it's at a diagonal. Probably not a real issue, but it has drawn my attention the whole time. It's supposed to be a 2.2M resistor (and that's what it's marked as (225), but in circuit, it measures only 7.2K, and it's the only SMT component that's crooked. Thanks! |
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