Author Topic: Battered Fluke 87 IV - Repair advice needed. (Read 15041 times)

LEECH666 · « **on:** May 02, 2012, 10:17:35 am »

Hi,

earlier today I bought a rather beat up Fluke 87 IV for for 20 Euros at a HAM fleamarket. I thought it was okay and only the LCD was shattered, but after I took a closer look I noticed that none of the functions are really working. All ranges seem to do weird stuff. The Fuses are missing but the insides look okay (optically).

I made a video showing the condition it's in.

And here are a few pictures of the boards inside.

http://imgur.com/a/gnih7#0

Secretly I am hoping it's just the broken displays fault that the meter does weird stuff but it probably isn't just that. Any advice?

I would also like to ask if anyone has any experience with the Fluke repair or customer service. I heard they charge fixed rates for their repair and it also includes calibration. Any idea how much it would cost me to get the DMM repaired?

Cheers,
Florian

HackedFridgeMagnet · « **Reply #1 on:** May 02, 2012, 10:41:26 am »

I would ...

By the look of it I think it's worth fixing.
So I would fix what I know is broken, and then retest it to see if something else is broken.

I guess you could also double check for damage on the input circuitry, and on anything that may be prone to shock.
At a guess the rest of it is probably fine.

ModemHead · « **Reply #2 on:** May 02, 2012, 01:15:51 pm »

My guess is that one of the series-connected input protection elements has opened up. I don't have any experience with that particular model, but on most Fluke handhelds I've repaired, there is a fusible resistor very near the V+ input jack that is in series with that input. This would be my first suspect. If it is open, you can bridge it with a regular 1K resistor just for testing purposes, to see if you get a more sane display. An "OL" on ohms range would be a good thing to see. Fortunately, the LCD seems to be working well enough so that you don't have to replace it ($$$) before fixing the other problems.

LEECH666 · « **Reply #3 on:** May 02, 2012, 03:22:17 pm »

I wonder if this service manual also includes the 87-4 or if it's just for the original 87 (83/85).

I read somewhere that the Fluke 87-4 is more like the Fluke 89. Actually the PCB says Model 89 Printed on the circuit board. However I can't find any manuals containing a circuit diagrams for those meters.

Oh and thanks for the tip with the fusible resitor, I will take a lookt at it once I have a spare moment.

ModemHead · « **Reply #4 on:** May 02, 2012, 04:18:36 pm »

Yes the 87-4 is different from all the rest of the 80-series. I think this is the correct service manual. Unfortunately, as with most newer stuff, it does not contain a schematic.

LEECH666 · « **Reply #5 on:** May 02, 2012, 04:41:17 pm »

Yeah, I guess they aren't meant to be user servicable.

I did an in circuit test of all the resitors near the input jacks. They seem to read okay (ohms mode). I get an OL reading on the Varistors (those two red blobs and the yellow one next to them) but that migt be normal. I've never worked with varistors so I don't know much about them.

Cheers,
Florian

ModemHead · « **Reply #6 on:** May 02, 2012, 05:55:46 pm »

Yes the varistors and spark gaps should be parallel to the input terminals and open, and any PTCs and fusible resistors should be in series with the input with fairly low impedance. I have trouble identifying those colored blobs sometimes too.

Further troubleshooting is going to be difficult without a schematic...

pullin-gs · « **Reply #7 on:** May 03, 2012, 12:01:18 am »

stick a fork in it...its done

LEECH666 · « **Reply #8 on:** May 03, 2012, 08:01:58 am »

Too crunchy, guess I have to ~~fry~~ stew it some more ...

Back to topic:

I think I might call Fluke later today and see if they can repair it and what they want for it.
If the money they want for the repair is under 200€ I might consider it, if it is higher than that I might attempt to fix it myself, tho that is probably hopeless without a schematic. There isn't even any silkscreen print on the pcb. A third option would be to put it on eBay "for parts" $:-\$ .

Florian

sonicj · « **Reply #9 on:** May 03, 2012, 11:53:12 pm »

the 87iv is the same (almost) as the 187 i believe...

heres the 87iv "service manual"

LEECH666 · « **Reply #10 on:** May 04, 2012, 09:02:52 am »

Thanks,

ModemHead already linked to that "service manual". Sadly it doesn't contain a circuit diagram

.
The Display works well enough to not replace it for the moment.

I did some more basic testing with my limited lab. I don't really have a variable PSU at hand, only a fixed one for an old radio set. Anyway so I fed the 13.8V (DC) to the Fluke and found out that the the V (DC) range seem to be broken. However the mV (DC) range seems to meassure the 13.8V just fine ... well almost. It displayed smth round about 13.78V while my Uni-T UT-61E and my Metrix MX24B showed round about 13.92V. I didn't check the specs of the Fluke but I am a bit astonished that the mV range goes up that high.

I shall investigate some more ...

ModemHead · « **Reply #11 on:** May 04, 2012, 11:48:04 am »

Quote from: LEECH666 on May 04, 2012, 09:02:52 am

... I am a bit astonished that the mV range goes up that high.

It shouldn't. Check that range switch very carefully. The meter has obviously had a serious fall or some kind of shock, so maybe some part of the switch mechanism is broken. Also, given the shock damage possibility, use magnification to look for cracks on the pcb.

bilko · « **Reply #12 on:** May 04, 2012, 12:53:18 pm »

Quote from: ModemHead on May 04, 2012, 11:48:04 am

Also, given the shock damage possibility, use magnification to look for cracks on the pcb.

It may be worth checking the surface mount resistors and caps as they may be cracked too.

LEECH666 · « **Reply #13 on:** May 04, 2012, 02:09:56 pm »

I already checked a few resistors near the the input jacks. Only in circuit tho. Looked ok to me. But I guess you can never be sure unless you desolder them. Haven't checked any caps.

In other news I just sent Fluke an email (couldn't get a hold of them on the phone) asking for a circuit diagram (most likely futile) and repair prices and if they still repair this particular model.

I might probe around some more later ...

Cheers,
Florian

LEECH666 · « **Reply #14 on:** May 04, 2012, 02:41:29 pm »

Ok I can't really rule out micro fractures in the traces or ceramic components, but so far the PCB doesn't look to be in bad condition. I already did some inspection with my 10x magnifier.

The worst case I could think of really is that the bonded wires inside the custom fluke ICs came loose.

Who knows ...

Cheers,
Florian

LEECH666 · « **Reply #15 on:** May 05, 2012, 09:16:51 pm »

Notice how in one of the pictures the V DC rang doesn't work (OL) but shows correctly on the mV DC range in the next picute.

Ohms Range and V DC seem to be broken. Can't test the Ampere ranges.

Did I tell you something new here? Probably not, but everyone likes pictures.
Well I do!

Cheers,
Florian

ModemHead · « **Reply #16 on:** May 05, 2012, 10:01:38 pm »

Looks like it is actually registering VDC on the mVDC range. And the VDC is OL, which could mean the bottom end of the divider is open. That seems to point to a malfunction in/around the range switch. The good news it that it seems to be measuring something correctly, so it may yet be repairable with enough perserverance.

LEECH666 · « **Reply #17 on:** May 05, 2012, 11:26:18 pm »

I think it actually landed on the display and the range switch because it has some sort of impact dent on the switch bar.

My main problem is probably that I don't know jack .... about multimeters, except some basic components on the inside from watching Daves videos.

The devider you talked about, is that perhaps what is also called "thick film resistor network"?

I have attached some more pictures. One of the tabs of the range switch probably broke off due to the impact.

Oh and thanks for trying to help, I hope I don't bore any of you with my picture spam and well this thread.

Florian

alm · « **Reply #18 on:** May 06, 2012, 12:15:43 am »

I would also expect this to be related to the range switch, although I don't see anything obviously wrong on the pictures. Maybe one of the contacts on the range switch is misaligned or has insufficient? It sounds like the contacts are in the VDC configuration on the mV setting, and the contacts don't make contact in the VDC setting. I would also try cleaning all of the contacts with something non-abrasive like a Q-tip with isopropanol.

You could try to figure out the connections for each of the mode settings, and manually short these contacts on the PCB (I would not solder to the contacts) to see if this has the same effect. Be sure to only use < 50 V voltages when working with the covers off.

LEECH666 · « **Reply #19 on:** May 06, 2012, 01:01:03 am »

I used Isopropanol after I took the last pictures, didn't help much. Anyway reverse engineering the rotary switch sounds like a good idea. Let me see what I can do.

Florian

//Edit

Visual reverse engineering.

I have to bridge violet vias to activate the faulty V DC mode.

LEECH666 · « **Reply #20 on:** May 06, 2012, 09:42:31 pm »

Just bought this ...

LEECH666 · « **Reply #21 on:** May 09, 2012, 01:16:51 am »

Guess I am going totally insane now ... I bought another Fluke 87 IV. This one is working tho. Waiting for it to get delivered (bought it in the UK, because in Germany measurement gear is pretty expensive).

Guess I will be able to do some comparative measurements. I did do some random probing yesterday but I didn't find out much. Some of the SMD parts are pretty hard to identify. Like there is this SOT23-6 part that has the code AAAM written on it. Google didn't bring up any results on that and none of the usual SMD part marking resources knew of that part.

I am also working on reverse engineering the circuit diagram from the board surfaces, however it seems to be a 4-Layer board so getting a complete shematic might prove difficult. A lot of work.

*sigh*

Florian

TheReverend · « **Reply #22 on:** December 28, 2015, 02:04:22 am »

Howdy,

the faulty meter is now in my hands and i was able to identify two broken smd parts. One 100k ohm resistor near the dial and another unknown part that you can see in the picture. does anybody have an idea what the unknown part may be?

LEECH666 · « **Reply #23 on:** December 28, 2015, 04:57:29 am »

Very nice work! And you found that fault so quickly too. Something I couldn't do in several years. I gave up after a while and didn't think about checking resistors for fractures I guess, even though, apparently, I already was already following the correct clues, *sigh*.

That looks like a precision (~~maybe laser trimmed~~ I meant custom value, unlabled) resistor to me, but that's just a guess. The S shaped track on the ceramic substrate is probably the resistive material. Kinda like in this picutre (just more curved):

I think it's a good idea to ask the question again in this thread: What's this please? (Component Advice)

Cheers,
Florian

//Edit: I have a working 87 IV so I could meassure the value of the resistor for you, if it turns out to be a resistor. I don't really want to desolder that part though, unless absolutely necessary.

LEECH666 · « **Reply #24 on:** December 28, 2015, 05:12:46 am »

Getting closer wit my picture searches ...

http://www.riedon.com/blog/tag/non-magnetic-resistors/

//EDIT

Vishay thick film resistor.

http://www.directindustry.com/prod/vishay/product-11633-535884.html


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Author Topic: Battered Fluke 87 IV - Repair advice needed. (Read 15041 times)

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