Fluke 77 service - Page 3

figge77 · 29th June 2009, 05:18 PM

yes i got the servicemanual, it includes a schematic.

when i was at it i changed the one electrolytic cap, but that didnt do anything any better. tought since its probably 20-25 years old.

gmphadte · 8th July 2009, 05:28 AM

I have this problem regularly, and normally I don't need that Meg range. This problem occurs because of the moisture in the pcb due to humid climate. Just heat the pcb under a 40-60watt bulb taking care not to heat the display.

Flange_UK · 10th July 2009, 08:58 PM

I repair a lot of Fluke meters at work but there have been a few of the old 77's and 23's with this MOhm fault that I just couldnt repair.

I put it down to a fault with the processor but didn't have any replacements to try.

anatech · 10th July 2009, 10:00 PM

Hi Flange_UK,
It must be leakage. It could develop in the PCB or divider, or some other component. There may even be moisture under the chip possibly. There is leakage somewhere, and the meter is only indicating what it "sees".

I wonder if sticking the meter in a warm, low humidity environment might work? It might be a week, but that is your best bet right now. If it wasn't such a good meter, you would probably never see this problem as it would be above the range of many others.

Have you cleaned out the function switch? You might want to try carefully removing it and clean it carefully. Hit it with some kind of moisture displacing fluid, then a zero residue cleaner. Lubricate the moving parts and contacts with some "barrier grease" Lithium might work. I've never tried that. Normally, I would have installed a new switch after cleaning the PCB underneath where the switch was.

I have a '77 I still use. It's great as an auxiliary meter on the bench. Heck, it's good enough as a main meter if that's all you've got.

-Chris

figge77 · 13th July 2009, 02:03 PM

well thanks for the info.

i´ll take a closer look at the switch.

btw are the 77 and 23 the same?

Flange_UK · 14th July 2009, 12:14 AM

The 77 and 23 are very similar but the 23 has a slightly better specification.

10th July 2009, 10:00 PM	#24
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Flange_UK, It must be leakage. It could develop in the PCB or divider, or some other component. There may even be moisture under the chip possibly. There is leakage somewhere, and the meter is only indicating what it "sees". I wonder if sticking the meter in a warm, low humidity environment might work? It might be a week, but that is your best bet right now. If it wasn't such a good meter, you would probably never see this problem as it would be above the range of many others. Have you cleaned out the function switch? You might want to try carefully removing it and clean it carefully. Hit it with some kind of moisture displacing fluid, then a zero residue cleaner. Lubricate the moving parts and contacts with some "barrier grease" Lithium might work. I've never tried that. Normally, I would have installed a new switch after cleaning the PCB underneath where the switch was. I have a '77 I still use. It's great as an auxiliary meter on the bench. Heck, it's good enough as a main meter if that's all you've got. -Chris __________________ "Just because you can, doesn't mean you should" © my Wife

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29th June 2009, 05:18 PM	#21
figge77 diyAudio Member Join Date: Apr 2009	yes i got the servicemanual, it includes a schematic. when i was at it i changed the one electrolytic cap, but that didnt do anything any better. tought since its probably 20-25 years old.

8th July 2009, 05:28 AM	#22
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	I have this problem regularly, and normally I don't need that Meg range. This problem occurs because of the moisture in the pcb due to humid climate. Just heat the pcb under a 40-60watt bulb taking care not to heat the display.

10th July 2009, 08:58 PM	#23
Flange_UK diyAudio Member Join Date: Jul 2009	I repair a lot of Fluke meters at work but there have been a few of the old 77's and 23's with this MOhm fault that I just couldnt repair. I put it down to a fault with the processor but didn't have any replacements to try.

13th July 2009, 02:03 PM	#25
figge77 diyAudio Member Join Date: Apr 2009	well thanks for the info. i´ll take a closer look at the switch. btw are the 77 and 23 the same?

14th July 2009, 12:14 AM	#26
Flange_UK diyAudio Member Join Date: Jul 2009	The 77 and 23 are very similar but the 23 has a slightly better specification.

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