URGENT! My Fluke 187 multimeter stopped reading voltages (ac and dc)

[The Guy]

Hi there,

Pretty much it. I was checking some high DC voltages in an amp I'm building (around 450V) and suddenly it stopped reading, went to test a 1,5v battery and nothing, changed the selector to mV and it gave me the correct reading.

What is happening? how can I fix this? I really need this multimeter working right now.

I'll appreciate any help.

Thank you

Guy.

[retiredcaps]

1. Post clear focused pictures of both sides of the pcb.

2. With no probes attached and rotary dial set to DCV, what does the lcd display?

3. With probes attached and shorted and rotary dial set to DCV, what does the lcd display?

4. With probes attached, what does the lcd show when you measure a 1.5V cell (in your description, nothing means nothing to us - that is, what does the lcd show)?

5. Do you have another meter to make measurements?

[The Guy]

1. Post clear focused pictures of both sides of the pcb.

2. With no probes attached and rotary dial set to DCV, what does the lcd display?

3. With probes attached and shorted and rotary dial set to DCV, what does the lcd display?

4. With probes attached, what does the lcd show when you measure a 1.5V cell (in your description, nothing means nothing to us - that is, what does the lcd show)?

5. Do you have another meter to make measurements?

Hi Retiredcaps,

Here are the answers:

1-  Pictures attached

2- 0.0000 VDC and the +/- sign changes very fast back and forth from + to -

3- Same as before

4- If I move the probes the numbers jump around from say 0.0020 VDC to 0.0200 VDC and when I measure the cell it goes to 0.0001 VDC stays there for a while and then drops to 0.0000 VDC +/- sign same as before

5- This is the only meter I have but tomorrow I might borrow one from a friend.

Just found out that if I measure a cell with the mV DC setting it actually measures the cell correctly but then once the probes are off the value keeps being displayed and then it drops VERY slowly.

Let me know if you need anything else.

Thanks a bunch.

[The Guy]

More pictures

[Twoflower]

Can you also post a picture of the rotary switch (the side that goes tot he PCB) please. The slow 'decay' might indicate a problem with the contacts.

The tracks on the contact fields looks reasonably worn. Can you also check if they are still intact. As of not worn through the metal to the FR4.

[alm]

Some of the switch contacts look very worn to me. To the point that I am wondering of there was sufficient lubrication on those contacts. Based on the symptoms (something seems open near the voltage divider), and the conditions (measuring a fairly high voltage), I would also look for open fusible resistors. If you have access to another DMM, I would also measure the resistance across the input terminals while the 187 is in various ranges. Should be 10 MOhm, but it would not surprise me if it was much higher, if not open circuit, on most ranges.

[coromonadalix]

check all the power resistors, the bridge rectifier, and the gray smt near the input plugs, i dont know if its a bead / ferrite / inductor  

Maybe search for a 83 87 series dmm schematics, easily found on the web, it should give you some ideas or hints ??

For the 187 189, you have a calibration manual on the web, it gives input impedances  and current on different inputs ...

[oldway]

More pictures

I am not a specialist and I have no service manual, nor schematics of this multimeter.....But the 1K resistance at the right side of the PCB seems to be a fuse resistor....did you check it ? How much is his resistance ?

If you don't have another multimeter, you could solder a 1K resistor in = only to check if it works again or not.
If it works, replace the fuse resistor by another one from Fluke for safety.

[oldway]

Be very carefull with this....
9V is too high voltage to play testing circuits of a multimeter...you can "kill" an IC and destroy your multimeter....

[alm]

Fine, I've removed it.

[oldway]

Fine, I've removed it.

Removing your post, you turn my message impossible to understand.....that's an unfair practice on a forum. 

Now i am obliged to quote all your posts, what will use a lot of space on the forum. This is nonsense....

[JFJ]

I'll appreciate any help.

You may find this blog helpful:
http://mrmodemhead.com/blog/fluke-87-fusible-resistor/

[The Guy]

I'll appreciate any help.

You may find this blog helpful:
http://mrmodemhead.com/blog/fluke-87-fusible-resistor/

Phew!! ...yup, that seems to be the problem. Pretty much the symptoms my fluke has. Will check that resistor in a while, gotta go to my friend's shop to borrow another dmm.

I was so scared that the chip was fried!

Thank you. Will report back.

(Btw, the connections in the rotary switch are perfect. Those like "grooves" that appear in the picture are a visual effect caused by the polished surface.) thanks everyone!

[ModemHead]

... Based on the symptoms (something seems open near the voltage divider), and the conditions (measuring a fairly high voltage), I would also look for open fusible resistors. If you have access to another DMM, I would also measure the resistance across the input terminals while the 187 is in various ranges. Should be 10 MOhm, but it would not surprise me if it was much higher, if not open circuit, on most ranges.

Seems like a good observation to me, esp. the bolded part.  Usually for a Fluke meter, the first section of the voltage divider resistor network is the 10 Meg "top" part of the divider.  In millivolts configuration, the downstream side of the 10 Meg is grounded by the analog processor, providing the expected 10 Meg input impedance, while the ADC input is taken from the ohms/diode sense path.  If something is open in this 10 Meg-to-ground path, it might explain the "decay" response, and the lack of response in Volts mode. This path would include switch contacts, the resistor network, and the analog processor itself.

Edit: changed my mind about the fusible resistor, it still might be open.

[Ian.M]

So you suspect the 1K 2W fusible resistor next to the board edge, but don't have another multimeter to check it with.   Patch in an ordinary 1K resistor directly across it and see if the meter reads correctly.  If so, order a suitable replacement, if not remove the extra resistor and look elsewhere for the fault.

However *DO* *NOT* *USE* it on any *VOLTAGE* *ABOVE* *50V* until you have replaced it with the proper resistor or an appropriately rated equivalent. 

[retiredcaps]

5- This is the only meter I have but tomorrow I might borrow one from a friend.

Here is where having another meter, even a free Harbor Freight one, helps.  The HF should be able to measure if the fusible resistor is open or not or close to 1k ohm. I wouldn't use the HF on the 450V amp as it might fail in more unpredictable ways, but for unpowered resistance measurements, it works fine.

BTW, you should also check the blue MOVs which should measure 0L (infinite) resistance.  The black PTC, just above the fusible resistor, should measure around 1.1k ohm.  All measurements can be done in-circuit.  If the MOVs or PTC don't measure as expected, then remove them and verify out of circuit.

edit: The 187 is one of my favourite meters.

[EHT]

With all due respect The Guy, it seems like you are a beginner? Fine for fixing the meter, but your main project has lethal voltages in it. I suggest you gain more experience on some low voltage circuits first - under 50V, nothing connected to AC line supply.

If you proceed with your high-voltage project my advice is get some insulated croc-clips, say like these (rated 600V or more):
http://www.fluke.com/fluke/uken/accessories/Test-Leads-Probes-and-Clips/AC175-Alligator-Clip-Set.htm?PID=76067

Then, when testing the voltages on your amp, clip the meter to the circuit you want to measure with the AC power unplugged, then turn it on safely away from the circuit. Make sure the case/isolated side of the PSU of the amp is earthed. Also note that the PSU Caps may hold charge for a while, especially if the amp isn't working and thus not drawing any current. You may wish to measure that so you know how long you need to leave it to discharge before touching it.

Once you proceed beyond testing the power you will really need a scope too.

Best of luck!

[Ian.M]

+1.

In addition to EHT's advice above, if there isn't a good, secure place to clip the + lead to for the measurement you need to make, and a good ground point for the - lead, solder a little loop of tinned copper wire to ther track, pad or terminal to provide a reliable secure connection point.

If there are any nicks or other damage to your meter's leads, replace them.  When ordering meter accessories, ONLY buy from the manufacturer or a major authorised distributor - its critically important for your safety to avoid buying possible fakes from EBAY.

If you end up having to do any signal tracing in your amp, not only will you need a scope, you will also need a scope probe with an adequate voltage rating - at least Cat II 600V.   Most switchable x1/x10 and many x10 probes will be unsafe to use on a valve project with a 450V supply rail.

[The Guy]

With all due respect The Guy, it seems like you are a beginner? Fine for fixing the meter, but your main project has lethal voltages in it. I suggest you gain more experience on some low voltage circuits first - under 50V, nothing connected to AC line supply.

If you proceed with your high-voltage project my advice is get some insulated croc-clips, say like these (rated 600V or more):
http://www.fluke.com/fluke/uken/accessories/Test-Leads-Probes-and-Clips/AC175-Alligator-Clip-Set.htm?PID=76067

Then, when testing the voltages on your amp, clip the meter to the circuit you want to measure with the AC power unplugged, then turn it on safely away from the circuit. Make sure the case/isolated side of the PSU of the amp is earthed. Also note that the PSU Caps may hold charge for a while, especially if the amp isn't working and thus not drawing any current. You may wish to measure that so you know how long you need to leave it to discharge before touching it.

Once you proceed beyond testing the power you will really need a scope too.

Best of luck!

Thanks EHT,

I am in fact a beginner, but I've been studying tube amp related electronics AND safety measures for almost a year now, and I think I am getting the hang of this. Recently I built my first guitar amp and it is playing like a charm. No hum at all and AWESOME sound! The only problem I have right know is a crackling noise in one of the channels.

This meter circuit and some of the components are new to me though.

I still need to borrow or buy me another DMM, today couldn't get one because caught the flu. Sucks.

[The Guy]

+1.

In addition to EHT's advice above, if there isn't a good, secure place to clip the + lead to for the measurement you need to make, and a good ground point for the - lead, solder a little loop of tinned copper wire to ther track, pad or terminal to provide a reliable secure connection point.

If there are any nicks or other damage to your meter's leads, replace them.  When ordering meter accessories, ONLY buy from the manufacturer or a major authorised distributor - its critically important for your safety to avoid buying possible fakes from EBAY.

If you end up having to do any signal tracing in your amp, not only will you need a scope, you will also need a scope probe with an adequate voltage rating - at least Cat II 600V.   Most switchable x1/x10 and many x10 probes will be unsafe to use on a valve project with a 450V supply rail.

Hey there, thanks for the tips. A scope is definitely on my list

That copper ground loop is installed, I already  figured that out when I was looking for a good and secure anchor for my ground lead

[The Guy]

5- This is the only meter I have but tomorrow I might borrow one from a friend.

Here is where having another meter, even a free Harbor Freight one, helps.  The HF should be able to measure if the fusible resistor is open or not or close to 1k ohm. I wouldn't use the HF on the 450V amp as it might fail in more unpredictable ways, but for unpowered resistance measurements, it works fine.

BTW, you should also check the blue MOVs which should measure 0L (infinite) resistance.  The black PTC, just above the fusible resistor, should measure around 1.1k ohm.  All measurements can be done in-circuit.  If the MOVs or PTC don't measure as expected, then remove them and verify out of circuit.

edit: The 187 is one of my favourite meters.

Hi Retiredcaps,

The 187 is a great meter! Has everything I need.

I already installed a 1.5K resistor over the 1k fuse resistor (didn't have a 1k) and nothing happened. Will test what you suggest as soon as i get another DMM

Cheers

[retiredcaps]

While you are waiting to get another meter and recovering from being sick, does resistance mode work at all?

Does the meter show 0L with no probes attached when set to resistance mode?

Does the meter show 0.2 ohms with probes attached and shorted when set to resistance mode?

[The Guy]

While you are waiting to get another meter and recovering from being sick, does resistance mode work at all?

Does the meter show 0L with no probes attached when set to resistance mode?

Does the meter show 0.2 ohms with probes attached and shorted when set to resistance mode?

Yep, yep and yep.... With probes attached and shorted it displays 0.13ohm

I just performed some fuether tests and it reads current, temperature, diodes and capacitance, it didn't read an 0047uf cap though it only displayed a flashing OL. But it did read an 047uf no problem.

[joeqsmith]

Hard to believe that sub 500VDC would do anything to your meter assuming it was in the DCV mode.   

Did you manual range the meter to make sure you did not take out an attenuator stage and the meter is just hunting now?  You may need to try a few different ranges.   

It would be funny if it was one or more attenuator stages and you had the meter in something other than DCV mode when the HV was applied.   I damaged my TPI meter this way and took out two attenuator stages. 

I understand they have a life time warranty.  Personally, I would have just sent it in to service.

[The Guy]

Hard to believe that sub 500VDC would do anything to your meter assuming it was in the DCV mode.   

Did you manual range the meter to make sure you did not take out an attenuator stage and the meter is just hunting now?  You may need to try a few different ranges.   

It would be funny if it was one or more attenuator stages and you had the meter in something other than DCV mode when the HV was applied.   I damaged my TPI meter this way and took out two attenuator stages. 

I understand they have a life time warranty.  Personally, I would have just sent it in to service.

I am possitive it was on VDC auto range.  In manual range it doesn't read anything right now. It just displays 0,0000

Will call to the service tomorrow and see if there is some kind of warranty.