Author Topic: Fluke 77 Repair & Teardown  (Read 15144 times)

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Offline voltlogTopic starter

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Fluke 77 Repair & Teardown
« on: March 01, 2016, 07:53:45 pm »
I recently did a repair of my Fluke 77 and wanted to share it. For the repair part all I did was replace a varistor that had some burn marks. I couldn't find the exact match so I replaced it with one of the same voltage but slightly bigger package. Luckily the Fluke 77 had plenty of space inside the case to accommodate the new varistor. It's amazing to see these meters still work after so many years of service. I think my particular unit was manufactured somewhere around 1987 and I got it at a recent auction. (data code on fluke marked chip). I hope you will enjoy this video. Thanks!

Offline retiredcaps

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Re: Fluke 77 Repair & Teardown
« Reply #1 on: March 01, 2016, 11:50:15 pm »
I downloaded your video a few days ago before your post, but now that I take a closer look and actually pay attention, the blown component in your video sure looks like spark gap (red component that is blackened looks like it has a cut in it).

At 3:37 of your video, it sure looks like a spark gap.

In addition, it looks like you may have the wrong schematic/service manual.  The original Fluke 70 series manual is at

http://www.testsell.co.uk/test_equipment_manuals/Fluke/Fluke%2070%20Series%20(PN731034%20January%201984%20Rev%201%2005-89)%20%20Service%20Manual.pdf

I cut and snip out the relevant portions for you.

The 70 series II uses slightly different components for input protection.

edit: PS. One other thing is that if one input component is blown, then I suggest all the other ones are possibly suspect.  I would test them.  Even if they are good, if the components available and cheap enough, I would replace them.
« Last Edit: March 01, 2016, 11:53:04 pm by retiredcaps »
 

Offline voltlogTopic starter

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Re: Fluke 77 Repair & Teardown
« Reply #2 on: March 02, 2016, 06:02:55 am »
You are right, thanks for the info. It seems I got the wrong service manual which lead me to a wrong repair being made. I replaced a 1.5KV spark gap with an MOV 910V. I initially though that was some kind of MOV with an integrated spark gap. The spark gap didn't look like it was blown, it probably just did its job and protected the input. I don't seem to find any replacements for this spark gap on any distributor though...

The only option is this thing on ebay(see screenshot bellow), but it looks like I would pay for shipping as much as I paid for the entire meter.
I measured the old spark gap and I'm getting 1kohm across it, now I'm thinking about putting it back inside if I don't find any replacement.
« Last Edit: March 02, 2016, 06:04:32 am by voltlog »
 

Offline retiredcaps

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Re: Fluke 77 Repair & Teardown
« Reply #3 on: March 02, 2016, 06:13:28 am »
The only option is this thing on ebay(see screenshot bellow), but it looks like I would pay for shipping as much as I paid for the entire meter.
Let me look around for a replacement.

Quote
I measured the old spark gap and I'm getting 1kohm across it, now I'm thinking about putting it back inside if I don't find any replacement.
A spark gap should measure infinite ohms.  At 1k ohms, it will definitely cause some funny readings.  You can measure E2 "in circuit" and verify that it is infinite ohms (with your Fluke 87).

The Fluke 77 will work with the spark gap removed, but you won't get the benefits of its input protection.
 

Offline voltlogTopic starter

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Re: Fluke 77 Repair & Teardown
« Reply #4 on: March 02, 2016, 06:23:39 am »
A spark gap should measure infinite ohms.  At 1k ohms, it will definitely cause some funny readings.  You can measure E2 "in circuit" and verify that it is infinite ohms (with your Fluke 87).

I cleaned the char marks on the spark gap with a small file and I am now reading infinite resistance on it's terminals. The one inside the unit is reading infinite ohms as well.
Now the spark gap probably doesn't have the same breakdown voltage but that was 20% tolerance anyway. If I don't find any alternatives, this goes back in.

Offline retiredcaps

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Re: Fluke 77 Repair & Teardown
« Reply #5 on: March 02, 2016, 06:31:28 am »
I cleaned the char marks on the spark gap with a small file and I am now reading infinite resistance on it's terminals.
Yes, that black residue/carbon can cause all sorts of havoc as per modemhead's blog entry below.

http://mrmodemhead.com/blog/ideal-carbon-footprint/

Seeing how the Fluke 70 series II went to a MOV/varistor in that position (E1 footprint), I wouldn't worry too much if E1 is a spark gap or varistor.

Some people here on this forum say that when they measure high voltage, they use their "cheaper" meters and save the "better" meters from potential abuse.  I'm somewhat the opposite.  If I'm measuring something high voltage, like 400V DC on a power supply, I'm grabbing my the meter that has the best input protection if I have an "oops" moment.  I care more about "me" than the "good meter".
 

Offline voltlogTopic starter

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Re: Fluke 77 Repair & Teardown
« Reply #6 on: March 02, 2016, 06:37:39 am »
Yes, that char residue was definitely conductive, after removing it the spark gap, got it's gap back.

Actually if you think about it, if they ditched the spark gap in a later model and kept only varistors they might of figured there is enough protection provided with just a varistor..
And I agree, I would also use a meter with good protection when working in any High Voltage/High Energy circuit.

Offline retiredcaps

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Re: Fluke 77 Repair & Teardown
« Reply #7 on: March 02, 2016, 06:44:50 am »
Actually if you think about it, if they ditched the spark gap in a later model and kept only varistors they might of figured there is enough protection provided with just a varistor..
Without an in depth comparison/analysis of the pcb layout, schematic, etc, the decision to switch may have not been that easy.   Other factors may have been considered.

I'm just saying for hobbyist's purposes, it is probably okay to have the varistor there in place of the spark gap given the  ebay price and shipping to your country.

Regardless, you got a good meter.  By today's standards, it is definitely weak in many areas, but still a good workhorse.
 

Offline voltlogTopic starter

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Re: Fluke 77 Repair & Teardown
« Reply #8 on: March 02, 2016, 06:51:58 am »
I like it because it looks like it can take some abuse inside a toolbox for example and survive just fine. I am not going to use it for electronics measurements on my bench, I have better meters for that job, but for general electrical work it should be fine.

Thanks!

Offline Stinger

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Re: Fluke 77 Repair & Teardown
« Reply #9 on: October 18, 2018, 06:48:01 am »
Hello friends,

I find an old Fluke 77.

Unfotunately, DMM mesure nothing.

After opening, R1 resistor is dead (infinite value).

Schematic show it's fusible resistor 1K ohm, 1%, 2W (RES, MF, 1K, +-1%, 100PPM, FLMPRF,FUSIBLE).

Can i replace R1 by this Metal film resistor ?

https://www.aliexpress.com/item/20pcs-2W-Metal-film-resistor-1-1R-1M-2-2R-4-7R-10R-22R-47R-100R/32847047012.html

Thank's for your help  :D
 

Offline voltlogTopic starter

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Re: Fluke 77 Repair & Teardown
« Reply #10 on: October 18, 2018, 07:19:20 am »
Fluke has chosen that resistor to be fusible so that it protects you and the meter in case of overload, you should be replacing it with the same type of resistor.

Offline Stinger

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Re: Fluke 77 Repair & Teardown
« Reply #11 on: October 18, 2018, 08:12:41 am »
Thank's for answer.
When you write about type, you mean classic metal film resistor with same value (1kohm, 1% 2w) ?
Are these resistors from link with metal films are used like fusible ?
 

Offline voltlogTopic starter

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Re: Fluke 77 Repair & Teardown
« Reply #12 on: October 18, 2018, 08:22:18 am »
Are these resistors from link with metal films are used like fusible ?
No, they are not. Fusible resistors will be clearly marked as such.

Offline retiredcaps

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Re: Fluke 77 Repair & Teardown
« Reply #13 on: October 19, 2018, 05:55:06 am »
Can i replace R1 by this Metal film resistor ?

https://www.aliexpress.com/item/20pcs-2W-Metal-film-resistor-1-1R-1M-2-2R-4-7R-10R-22R-47R-100R/32847047012.html
For a multimeter, the fusible resistor is part of the input protection.  I wouldn't trust anything from ebay, aliexpress, etc for some an important component.  You have no idea of the quality, if any, of these parts.

Get the proper resistor from a reputable company like digikey, mouser, etc.
 

Offline Stinger

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Re: Fluke 77 Repair & Teardown
« Reply #14 on: October 20, 2018, 05:08:23 pm »
Thank's for prompt response.

It's possible to replace this fusible resistor by ceramic fuse ?
 

Offline kkritsilas

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Re: Fluke 77 Repair & Teardown
« Reply #15 on: October 21, 2018, 01:45:44 am »
I just got a what appears to be a very old Fluke 77. It does’t have the 10A fuse, and the front panel of the meter does have “UNFUSED” below the 10A designatir near ttye 10A input.

Meter wotks fine, aside from some LCD ghosting (probably needs new Elastomeric strips, and maybe cleaning of the LCD contacts on the PCB). The other issue, and why I am posting, is that the top right hand screw is not clamping down properly. When I opened the meter to replace the battery and clean up the selector switch, I did not see any cracking of the screw post that this screw fits into. I can only conclude that whoever had this meter in the past must have repeatedly put in this self tapping screw in a way that has bascally enlarged the screw whole to the point that the screw isn’t getting much if a “bite” any more.

I have thought of trying to add a thin layer of epoxy glue to try to get more thread engagement, or getting a slightly bigger self tapping screw. Both have drawbacks. Has anybody attempted a repair like this before, and what worked?

P.S. i hate self tapping acrews into plastic, especially ones that need to be removed repeatedly (to reolace the battery).

P.P.S. I have enclosed a couple of pictures of my Fluke 77. Note the lack of a 10A/11A fuse, abd that thw Board says it is a Fluke 7X, Rev. D.
« Last Edit: October 22, 2018, 06:52:28 am by kkritsilas »
 

Offline lowimpedance

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Re: Fluke 77 Repair & Teardown
« Reply #16 on: October 21, 2018, 03:57:56 am »
Thank's for prompt response.

It's possible to replace this fusible resistor by ceramic fuse ?
NO , get the required 1 K FUSIBLE RESISTOR  and do a proper repair.
Your safety and anyone else that may use it may depend on it , don't cut corners here.
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline coromonadalix

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Re: Fluke 77 Repair & Teardown
« Reply #17 on: October 21, 2018, 04:01:33 am »
Repaired some case meters screws threads and screws posts with baking soda powder and crazy glue ....  tried some tests before to see how fast it cure and playing with baking soda layer thickness

It hold pretty well and is strong too, re-threaded with an screw in forward and reverse motion going slowly down in the hole.
 
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Offline tpowell1830

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Re: Fluke 77 Repair & Teardown
« Reply #18 on: October 21, 2018, 06:08:16 am »
I miss my old 77, the one that you got is a beauty, looks almost new.

I would love to get an old 87 or 77 again, what was the price for yours? Unfortunately, I lost my 77 a few years ago, as I mentioned in this post https://www.eevblog.com/forum/chat/classic-analog-moving-coil-multimeter-which-are-considered-best-ones/msg1449434/#msg1449434 but, I loved the rugged boot and crisp characters.
PEACE===>T
 

Offline coromonadalix

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Re: Fluke 77 Repair & Teardown
« Reply #19 on: October 21, 2018, 10:10:31 am »
A video teardown :

Had the chace of using one in my old job,  crisp display, loved the one range AC and DC, never used the 300mv range.
 

Offline Stinger

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Re: Fluke 77 Repair & Teardown
« Reply #20 on: October 22, 2018, 09:03:43 am »
Thank's for prompt response.

It's possible to replace this fusible resistor by ceramic fuse ?
NO , get the required 1 K FUSIBLE RESISTOR  and do a proper repair.
Your safety and anyone else that may use it may depend on it , don't cut corners here.

Thank you. I sended e-mail at Fluke for resistor. :-+
 

Offline Stinger

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Re: Fluke 77 Repair & Teardown
« Reply #21 on: October 22, 2018, 07:31:56 pm »
I miss my old 77, the one that you got is a beauty, looks almost new.

I would love to get an old 87 or 77 again, what was the price for yours? Unfortunately, I lost my 77 a few years ago, as I mentioned in this post https://www.eevblog.com/forum/chat/classic-analog-moving-coil-multimeter-which-are-considered-best-ones/msg1449434/#msg1449434 but, I loved the rugged boot and crisp characters.
We can't measure capacitors with Fluke 77. :(
 

Offline tpowell1830

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Re: Fluke 77 Repair & Teardown
« Reply #22 on: October 22, 2018, 07:56:34 pm »
I miss my old 77, the one that you got is a beauty, looks almost new.

I would love to get an old 87 or 77 again, what was the price for yours? Unfortunately, I lost my 77 a few years ago, as I mentioned in this post https://www.eevblog.com/forum/chat/classic-analog-moving-coil-multimeter-which-are-considered-best-ones/msg1449434/#msg1449434 but, I loved the rugged boot and crisp characters.
We can't measure capacitors with Fluke 77. :(

I didn't really say that I wanted to measure capacitance. Yes, true, limited measurements, but that is not why I want to get one, or an old 87. I just want to know what a good used one costs, so I can replace mine.
PEACE===>T
 

Offline retiredcaps

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Re: Fluke 77 Repair & Teardown
« Reply #23 on: October 23, 2018, 04:19:56 am »
An used Fluke 87 series 1 should cost around $100 USD on ebay.  An used Fluke 77 should be around $50 USD.

Pawn shops might yield some bargains.
 
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Offline coromonadalix

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Re: Fluke 77 Repair & Teardown
« Reply #24 on: October 24, 2018, 12:18:26 am »
Fluke 87 have capacitance but not high values, first series was around 5 uf  up to the 87 serie V who goes at 10,000 uf

But it is not an true capacitance meter with esr    etc ...

And the most annoying functions "87V"  are they start in AC mode  you have to toggle it in DC    a big no no for me.

Used and working Fluke 187 189 are selling pretty high  200-250$ usd range they go up to 50,000 uf, and they are 50,000 counts displays

For an serie 87,  goes for the 87 (no roman letters means the first serie) or the serie 87 III (serie 3)  at 20,000 count display it will be good enough for you.
The 87 IV  is like an fluke 187, but i heard they had some ranges lags problems ???   The 187 had not this problem ?

You have Brymen, Fluke, Agilent, old Wavetek or Beckman Industrial  ... any good reputable brands. Skip low end Uni-T meters, i think they are somewhat good starting with the UT-131 UT-181 ?? 

Personally, i avoid any oled based display meters.


Take you time to find an good reputation used clean meter and add an Deer De-5000 in your collection.
 


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