Author Topic: Fluke 89 IV - powers up, measures nothing  (Read 9288 times)

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Offline asdqwerty

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Fluke 89 IV - powers up, measures nothing
« on: June 05, 2016, 05:53:17 pm »
Fluke 89 IV:
Last time it was successfully used, it was used to check 3~ capacitors and voltage.
Some days later it was to be used to measure some resistance.
But it shows 0.00 ohm, it beeps when switching to beep mode. It should read OL, before start.
Switching to voltage gves 0.00.
Althoug at times, it might rush around displaying any number, both it resistance and voltage mode. But for the most 0.00 and it does not matter what the test leads do. Open, connected to something or shorted.

Fuses are checked, batteries changed. Still the same.
So it seems like something in the input stage might have a break / gap.

Tested with a different ohm-meter, by setting one test lead in the input-socket, and followed the pcb. I got a reading in front or after all the components it seems. Nowhere there was OL, it varied from few ohm to a lot of ohms. Don't know if its a lead... :-//

Anyone have any idea of which component to investigate more or try to change??
There are pictures of the 89 PCB on google and this site.
 

Online Monkeh

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #1 on: June 05, 2016, 05:56:57 pm »
Take the MOVs out and see what you get.
 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #2 on: June 05, 2016, 06:13:42 pm »
I'm having a hard time following what works and doesn't.  As such, let's get a baseline.

Q1. If you measure a 1.5V AA cell, do you get 1.5V or 0.0V?
Q2. If you short the probes with meter set to DCV, do you get 0.0V?
Q3. If you short the probes with meter set to resistance, do you get roughly 0.2 ohms?
Q4. If you remove the leads with meter set to resistance, do you get 0L?
Q5. If you measure a 1k ohm resistor, do you get 1k ohm?
 

Offline asdqwerty

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #3 on: June 05, 2016, 07:03:31 pm »
Q1: 0.0V
Q2: ~0.0V  -> no change with probes shorted or not
Q3: 0.00 - same with probes open or removed
Q4: No, it says 0.00
Q5: No, it says 0.00

Resistance reads 0.0 , while  VAC and VDC may have the last digits run up or down.
Holding "hold" while power up shows the lcd-dispay test.

I think the meter is working, but there is a gap in the signal path..

Also tried the mA and A, with the current in a ledflashlight.
No readings.
So it seems all 4 inputs are out of order, or the one thats common for all...
« Last Edit: June 05, 2016, 07:08:20 pm by asdqwerty »
 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #4 on: June 05, 2016, 07:50:07 pm »
Well, if we use this picture from

https://www.eevblog.com/forum/repair/fluke-89-iv-repair-after-input-overload/

as a reference, check the following components all "in-circuit".

Q6. The 1k fusible resistor (circled in green) should read 1k ohm using another working multimeter.
Q7. The three green resistors (circled in blue) marked 100k ohm should read 100k.
Q8. The yellow component (circled in yellow) with a cut through it is a spark gap.  It should read 0L or open with another working meter.
Q9. The two red components (circled in red) are MOVs.  They should read 0L or open with another working meter.
Q10. The brown/grey component (circled in brown) between the fusible resistor and 100k ohm resistor is a PTC.  It should read around 1k ohm.

Report your readings for Q6-Q10.
« Last Edit: June 06, 2016, 08:08:04 pm by retiredcaps »
 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #5 on: June 05, 2016, 07:58:36 pm »
@asdqwerty, please post clear focused pictures of YOUR board so we can see if there are differences.  Please provide pictures of both sides of the pcb and one close picture of the COM jack solder area (i.e. 3 pictures in total).
 

Offline asdqwerty

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #6 on: June 05, 2016, 08:53:18 pm »
Q6: Reads 3.5 Kohm - it is marked 3.5Kohm also
Q7: They read 100K
Q8: Says OL
Q9: The one closes to the yellow with a gap read 11.6Mohm and 11.9Mohm when changing polarity. The other one is OL.
Q10: Reads 1.15Kohm

All measured with a Fluke 189.

Its a slightly different PCB it seems.

BTW thanks for taking your time. :)
 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #7 on: June 05, 2016, 09:01:40 pm »
Q9: The one closes to the yellow with a gap read 11.6Mohm and 11.9Mohm when changing polarity. The other one is OL.
Looks like Monkeh has the right idea.  The MOV reading 11.6M ohm might be bad.  Remove it has Monkeh suggests and retest Q1-5.  Also measure the removed MOV out of circuit just in case something in-circuit is affecting the resistance measurement.  If the MOV still reads 11.6M ohm, it is definitely bad.
« Last Edit: June 05, 2016, 09:13:19 pm by retiredcaps »
 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #8 on: June 05, 2016, 09:04:27 pm »
BTW, the contacts on the rotary switch could use a good cleaning with IPA (unless it is light photography trick?).  Another reason to see pictures of YOUR pcb and not one already posted here or on the Internet.
 

Offline asdqwerty

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #9 on: June 05, 2016, 09:09:55 pm »
One more picture
 

Offline asdqwerty

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #10 on: June 05, 2016, 09:18:12 pm »
Another one
 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #11 on: June 05, 2016, 11:41:46 pm »
Also tried the mA and A, with the current in a ledflashlight.
No readings.
Hmm, I missed your edited statement above.  Let's see if removing the suspect MOV first fixes V/ohm.  Then you can retest the current measurements.   One problem at a time.
 

Offline asdqwerty

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #12 on: June 06, 2016, 09:16:07 am »
I removed the actual MOV. It gives a readout OL when tested.
Placing the test-probes on the soldering points of the MOV gives 11,4Mohm, so thats where it came from.
I then put back the MOV. No change.

When putting the multimeter on VAC, it says OL for a short while, then displaying results in the range of 450-500 V, when test-probes are not connected.
VDC = 0.00
Ohm = 0.00

 

Online Monkeh

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #13 on: June 06, 2016, 09:18:59 am »
11Mohm sounds familiar.

Put it in VDC and manually change the range, see if you get sensible readings.
 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #14 on: June 06, 2016, 09:24:13 am »
Regarding the dirt on the your 89IV rotary switch as per your pictures, see

http://mrmodemhead.com/blog/fluke-83-iii-rotary-switch/

Give them a clean.
« Last Edit: June 06, 2016, 09:34:08 am by retiredcaps »
 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #15 on: June 06, 2016, 09:35:17 am »
Placing the test-probes on the soldering points of the MOV gives 11,4Mohm, so thats where it came from.
Those two soldering points should definitely read open circuit.
 

Online Monkeh

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #16 on: June 06, 2016, 10:33:57 am »
Placing the test-probes on the soldering points of the MOV gives 11,4Mohm, so thats where it came from.
Those two soldering points should definitely read open circuit.

If the meter is switched on at the time, you should read across the input impedance - 11.4Mohm is not far off the mark. Assuming it's a single MOV design, not the series arrangement some Fluke models use. I'm not familiar with the specific circuit here, but that figure is.. rather close to what I expect to see across the input.
 

Offline asdqwerty

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #17 on: June 06, 2016, 11:00:27 am »
Maybe worth mentioning... the multimeter was exposed to rain late last summer. It was forgotten outdoor, and quite wet. But after drying, it has worked flawlessly since. At least 8-9 months..
--

So I tested more, cleaned the rotary-switch circuit, and put on a tiny solderingtip on the switch itself, in case the pressure isn't sufficient to make a steady contact. But no difference.
 
It doesn't behave 100%the  same every time:

Either VDC started working, or I tested too few times.
But now, VDC is working 9 of 10 times. My bench-powersupply gives 2-15VDC and it reads as expected. (auto and manually)
mVDC however is steady 0.00. - It shoud read like 2900mV @2.9v - The 189 does that.
Ohm-setting 99.99% of the time shows, steady 0.00 Ohm  - the beeper mode beeps all the time.
VAC is totally wrong. Often peaks at OL and the bar indicates >1000V
Or it is around -0- , and when I try the wall-outlet it says 40-50 or 65-75 or doesn't react.
Or it displays approx 450VAC with no probes, and runs up and down.

Amps gives nothing. 0,0A 0,0mA -Lightbulb/led in the flashlight is lit.

The measuring done with the MOV out of the pcb was done with no power attached.
 
« Last Edit: June 06, 2016, 11:03:20 am by asdqwerty »
 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #18 on: June 06, 2016, 02:14:18 pm »
Maybe worth mentioning... the multimeter was exposed to rain late last summer.
Can you remove the LCD from the pcb and post clear focused pictures of the front and back pcb?  After I see pictures, I have more test/measurement suggestions.
 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #19 on: June 06, 2016, 03:14:36 pm »
Can you also replicate my 4 measurements using just 1 set of probes shown in the pictures?  Assume my 187 = non working 89IV and my 77 III is the "good" meter.
 

Offline asdqwerty

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #20 on: June 06, 2016, 04:03:57 pm »
Here are more pcb pictures  - part 1
 

Offline asdqwerty

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #21 on: June 06, 2016, 04:06:20 pm »
part 2
 

Offline asdqwerty

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #22 on: June 06, 2016, 04:10:31 pm »
Measurements
 

Offline asdqwerty

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #23 on: June 06, 2016, 04:23:14 pm »
Additional comment:

Measurement picture 2:
If I on the faulty 89IV press "range" and cycle through the manual ranges, it affects the readout on both meters.
Like:
519K - 1.13Vdc
0,12M - 0.38Vdc
2.44K - 4.83Vdc
37.5K - 2.83Vdc
Auto - as picture

It also had a small impact of the current measurement, leading to decreasig current to almost zero.

 

Offline retiredcaps

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Re: Fluke 89 IV - powers up, measures nothing
« Reply #24 on: June 06, 2016, 04:30:28 pm »
I need a break to digest all this.  I'm participating on your 89IV, defective BM-235 and now Velleman 9912 all at the same time.  It is all starting to blur together.

I'm also gone for a few hours later this afternoon.
 


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