Fluke 117 problem with 6 and 60 MOhm scales - FIXED !

[Original]

Hello,

I have recently salvaged a badly abused fluke 117 multimeter. All scales seem to be working pretty well within spec except the 6 and 60MOhms.
The 6MOhms is off about 5% compared to my Fluke 189.
The 60Mohms range (and idle in autorange) stops at about 13.57MOhms (fluctuating).

The PCB is very clean and nothing appears blown.

The voltage on the terminals for 6MOhms is 0.6V and for 60Mohms is 0.375V.

In circuit, with the meter off the movs and thermistors etc measure:

RV1 7 MOhm
RV3 4.70 MOhm
RV2 3.77 MOhm

Fusible resistor 1045 Ohm
RT1       1103 Ohm
RT2        983  Ohm

Please be kind enough to help me repair this meter.
Thanks,

Chris

[retiredcaps]

In circuit, with the meter off the movs and thermistors etc measure:

RV1 7 MOhm
RV3 4.70 MOhm
RV2 3.77 MOhm

Fusible resistor 1045 Ohm
RT1       1103 Ohm
RT2        983  Ohm

All three MOVs, R1, R2, and R3 are bad.  You can remove them from the 117 for test purposes and the 6 and 60M ohm readings should be within spec.  All three MOVs, out of circuit, should read 0L resistance with another working meter.

The fusible resistor and two PTCs, RT1 and RT2, are fine.

Report your findings and if the removal of the MOVs fixes the problems, then we can suggest replacements from mouser/digikey.

[Original]

And of course you are absolutely right! the movs are blown...
Can you please suggest alternatives? Any source is good.

Thanks again

edit: I have just found https://www.eevblog.com/forum/testgear/fixing-a-fluke-87v/ are there any better alternatives?

[retiredcaps]

And of course you are absolutely right! the movs are blown...

In your original picture, I could see a bit of black on the MOV so I suspected they were bad and your in circuit measurements confirmed so.

edit: I have just found https://www.eevblog.com/forum/testgear/fixing-a-fluke-87v/ are there any better alternatives?

The above thread has the suggested one.

[retiredcaps]

Just curious, did you get this for free from a recycle bin?  Or from a colleague?

[Original]

It was used onboard a ship. The chief engineer no longer trusted it because of the above issue.
Also the faceplate has completely faded away.
Any ideas where i could find a replacement top cover?

[retiredcaps]

The chief engineer no longer trusted it because of the above issue.

That is reasonable.

Also the faceplate has completely faded away.
Any ideas where i could find a replacement top cover?

You can try Fluke.  The top cover is part number 2525553 as per Fluke 11x calibration manual page 18.

Alternatively, I have seen replacement top covers on ebay.com from time to time.

Keep in mind that it might be very expensive.  If this were my meter, a white sharpie or a label maker would suffice.