Fluke 8060A accidentally killed resistance function - need help

[EE-digger]

I have several 8060A DMMs.  One I bought new 34 years ago !  The other I bought new (NOS) last year.

The latter was being used to measure high voltage from an ESD simulator thru a high value, high voltage resistance.

Unfortunately, I accidentally set the ESD gun a bit too high and 12 to 15kV arc'ed across the HV Gohm resistor, to the + terminal on the meter.

The voltage ranges still work fine.  They work fine even through a resistance, indicating that the series VARs have not developed high, non-linear leakage.

Ohms are totally messed up and the readings have no relation to the resistance being measured, from 0 ohm shunt up to megohms.


What else I've found:

Voltage and currents present at the jacks across the resistance ranges are correct, matching the service pages and the good meter.
Conductance on the bad meter does go to zero, BUT will show a response if I wave a hand around the face of the meter.  My good meter does not do this.

I did not wrap my head around the entire design yet but my current thinking is that possibly D2, D3 were blown by the hundreds of volts which would have been developed across the VARS during clamp of the ESD discharge  .  Then, this current, through a 50k series resistance, may have taken out the "O REF -" on pin 12 of the MAC.

I welcome your thoughts on this.  I think the best clue may be the response to a hand wave on various ranges.  Some device has been taken out, leaving some node floating, but its not clear which ... and there aren't many active devices in the path to begin with.

[retiredcaps]

I have several 8060A DMMs.

How many if I may ask?  The reason I ask if you have any partially or non working 8060A, they may be useful in swapping parts for troubleshooting purposes.

Ohms are totally messed up and the readings have no relation to the resistance being measured, from 0 ohm shunt up to megohms.

What ohms readings do you get when measuring the following?

1. shorted probes
2. 1k resistor
3. 10k resistor
4. 100k resistor
5. no probes connected to meter

[TerraHertz]

A year ago I did something similar to a Fluke 77 multimeter. Applied voltage while it was on ohms range. Sigh. I think it was AC Mains, but can't recall for sure.
Everything else still works, but the ohms range acts bananas.
With open circuit, it correctly displays O.L Mohms.
Short circuit, display blinks a few times, then a value around 300, but this continually drifts down slowly. Around 150 after a minute, still going down but slowing. Like there's a large cap involved, being charged/discharged slowly.
1K resistor: Initial display about 1280, declining slowly towards around 1040.
100R  Momentarily displays around 340, then starts randomly flickering "OL." and "-OL." with the range bar also flickering wildly.

At the time I just accepted it's blown, probably not repairable, and I'm an idiot.
If anyone can suggest some approach for the meter I'd appreciate it. The idiocy I'll just have to live with forever.

[retiredcaps]

If anyone can suggest some approach for the meter I'd appreciate it. The idiocy I'll just have to live with forever.

I suggest deleting your post above and opening a new thread for your problem so we don't confuse everyone with two different meters and possibly two different problems in one thread.

Once you post in a new thread, I can make suggestions.

[EE-digger]

I have two but may pick up a cheap 3rd if I need the MAC chip.

Here's the behavior:

1. zero ohm shunt - roughly 11 ohms, touching or gently grabbing (no squeezing) the case changes +/- 3 ohms or so
    drifted up to 30 ohms after sitting a few minutes

2.  1k resistor - 0.574k
3.  10k resistor - 4.75k on 20k range,  974 on 2k range
4.  100k resistor - 48k on 200k range,  8.8k on 20k range

5.  open - drifts to overrange on any resistance range

After a few minutes, reapplied the 100k and it read 8k,  repeated a few minutes later, it read 11k.

Also, this meter has a screw in the battery cover and is a Fluke vs my old John Fluke.  (SN 68xxxxx vs old 42xxxxx)

[retiredcaps]

From your ohms readings, I suspect possibly one or more of the input protection components are bad.

Anytime you have an "oops" moment, I suggest testing all the input protection components as it's quick and simple.  It takes less time to test them than it takes me to write out the procedures below.

1. Measure the resistance of the MOVs (RJ1, RJ2, RJ3 and RJ4).  They should all read open circuit with a working 8060A.
2. Measure the resistance of the PTC (RT1).  It should read around 1kohm +/- 40%.

Report actual readings for above.

If the MOVs are not open circuit, you can remove them for test purposes.  If the PTC is out of spec, you can put in a normal 1k ohm resistor for test purposes.

PS. The 8060A service manual is available to show the locations of the above.

[EE-digger]

FIXED 

Thanks to you !  I never would have checked RT1 because I wouldn't have believed an ESD strike could take it out.  I do a lot of work with ESD and protection designs (mostly protection of high speed digital, analog I/O) but am not familiar with this fusible part.

The simulator delivers a normal IEC ESD waveform.  So we're talking a few nanoseconds for the major peak and possibly around 10 amps.  The secondary peak is about half the current but is about done by 200ns.  For its physical size, I don't understand how the part could respond but it did its job.

Thanks for your help !  All ranges are still spot on.

[retiredcaps]

I never would have checked RT1 because I wouldn't have believed an ESD strike could take it out.

I buy used and abused Flukes and checking the input protection is simple and easy to do.

For a replacement, I think YS4020 is suitable as its 1km 1000V PTC.  You can find it at mouser and digikey.

https://www.mouser.com/datasheet/2/18/amphenoladvancedsensors_YS4020-1157120.pdf

For its physical size, I don't understand how the part could respond but it did its job.

I'm not an expert in exactly how they work, but see

[EE-digger]

That's a PTC and you don't want it in your front end.  At overload, it will ramp to a high resistance and stay there until the overload is removed.  While in that state, it will still be delivering current at its high resistance (not spec'd for the YS series, it appears).

The fusible parts fuse and stay open.  On a typical (not engineer with new ESD gun) overload of ac or dc, it blows and keeps on protecting).

I'm still impressed that the original part blew with an ESD discharge.  Usually, I see this in physically small parts, like 0402 and smaller resistors and caps.

There's also this part, from a vintage radio discussion, also in stock at Mouser.  It has a fuse time curve in the datasheet.  Nothing in nanoseconds but still pretty fast with a huge voltage application.  It is the SPH series from IRC (now TT) which the original Fluke is claimed to be:

https://www.mouser.com/ProductDetail/IRC-TT-Electronics/SPH1001J/?qs=sGAEpiMZZMtbXrIkmrvidGHZvmjVF%2FpZVeMYPzYGJy8%3D

[retiredcaps]

Let's refer to the service manual at Fluke's website

http://assets.fluke.com/manuals/8060a_3vimeng0200.pdf

R1 and R2 according to the BOM and schematic are 1k ohm fusible resistors.

RT1, is a thermistor or PTC.

Your posts seems to indicate RT1 is/was bad.  If yes, then that should be a PTC, not a fusible resistor.

Screenshots of the relevant are posted.

[EE-digger]

I am so sorry and embarrassed.  Must be a senior moment or one too many ESD discharges.

It was R1 that was open.

[retiredcaps]

R1 = fusible resistor = open. Seen that before.  See

http://mrmodemhead.com/blog/fluke-87-fusible-resistor/

[retiredcaps]

I am so sorry and embarrassed.

No problem.  Of the 3,383 posts here, I'm 100% sure I have made my share of mistakes.

Going back to correct or update them with better information would be a lifetime project.

I'm glad you got it working.

BTW, if you haven't seen this 8060A thread, you might find several hours worth of entertainment.  See

https://www.eevblog.com/forum/testgear/old-fluke-multimeters/

That and modemhead's blog.

http://mrmodemhead.com/