Fluke 77 Repair & Teardown - Page 1
Forum section: electronics / repair

author: voltlog
author_rank: Regular Contributor
timestamp: March 01, 2016, 07:53:45 pm
content: 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!

author: retiredcaps
author_rank: Super Contributor
timestamp: March 01, 2016, 11:50:15 pm
content: 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 athttp://www.testsell.co.uk/test_equipment_manuals/Fluke/Fluke%2070%20Series%20(PN731034%20January%201984%20Rev%201%2005-89)%20%20Service%20Manual.pdfI 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.

author: voltlog
author_rank: Regular Contributor
timestamp: March 02, 2016, 06:02:55 am
content: 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 02, 2016, 06:13:28 am
content: Quote from: voltlog on March 02, 2016, 06:02:55 amLet me look around for a replacement.QuoteA 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.

author: voltlog
author_rank: Regular Contributor
timestamp: March 02, 2016, 06:23:39 am
content: Quote from: retiredcaps on March 02, 2016, 06:13:28 amI 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 02, 2016, 06:31:28 am
content: Quote from: voltlog on March 02, 2016, 06:23:39 amYes, 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".

author: voltlog
author_rank: Regular Contributor
timestamp: March 02, 2016, 06:37:39 am
content: 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 02, 2016, 06:44:50 am
content: Quote from: voltlog on March 02, 2016, 06:37:39 amWithout 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.

author: voltlog
author_rank: Regular Contributor
timestamp: March 02, 2016, 06:51:58 am
content: 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!

author: Stinger
author_rank: Regular Contributor
timestamp: October 18, 2018, 06:48:01 am
content: 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.htmlThank's for your help

author: voltlog
author_rank: Regular Contributor
timestamp: October 18, 2018, 07:19:20 am
content: 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.

author: Stinger
author_rank: Regular Contributor
timestamp: October 18, 2018, 08:12:41 am
content: 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 ?

author: voltlog
author_rank: Regular Contributor
timestamp: October 18, 2018, 08:22:18 am
content: Quote from: Stinger on October 18, 2018, 08:12:41 amNo, they are not. Fusible resistors will be clearly marked as such.

author: retiredcaps
author_rank: Super Contributor
timestamp: October 19, 2018, 05:55:06 am
content: Quote from: Stinger on October 18, 2018, 06:48:01 amFor 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.

author: Stinger
author_rank: Regular Contributor
timestamp: October 20, 2018, 05:08:23 pm
content: Thank's for prompt response.It's possible to replace this fusible resistor by ceramic fuse ?

author: kkritsilas
author_rank: Contributor
timestamp: October 21, 2018, 01:45:44 am
content: 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.

author: lowimpedance
author_rank: Super Contributor
timestamp: October 21, 2018, 03:57:56 am
content: Quote from: Stinger on October 20, 2018, 05:08:23 pmNO , 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.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 21, 2018, 04:01:33 am
content: 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 thicknessIt hold pretty well and is strong too, re-threaded with an screw in forward and reverse motion going slowly down in the hole.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: October 21, 2018, 06:08:16 am
content: 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 posthttps://www.eevblog.com/forum/chat/classic-analog-moving-coil-multimeter-which-are-considered-best-ones/msg1449434/#msg1449434but, I loved the rugged boot and crisp characters.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 21, 2018, 10:10:31 am
content: 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.

author: Stinger
author_rank: Regular Contributor
timestamp: October 22, 2018, 09:03:43 am
content: Quote from: lowimpedance on October 21, 2018, 03:57:56 amThank you. I sended e-mail at Fluke for resistor.

author: Stinger
author_rank: Regular Contributor
timestamp: October 22, 2018, 07:31:56 pm
content: Quote from: tpowell1830 on October 21, 2018, 06:08:16 amWe can't measure capacitors with Fluke 77.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: October 22, 2018, 07:56:34 pm
content: Quote from: Stinger on October 22, 2018, 07:31:56 pmI 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: October 23, 2018, 04:19:56 am
content: 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.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 24, 2018, 12:18:26 am
content: 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 ufBut 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 displaysFor 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 problemsThe 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.

author: Stinger
author_rank: Regular Contributor
timestamp: October 29, 2018, 11:41:59 am
content: Hello,About dead R1 fusible resistor 1K ohm, 1%, 2W (RES, MF, 1K, +-1%, 100PPM, FLMPRF,FUSIBLE), can be replaced by this ?ROYAL OHM FRN02WK0102A10Résistance: metal film; protection; THT; 1kΩ; 2W; ±10%; Ø5x12mmhttps://www.tme.eu/fr/details/nfr2w-1k/resistances-de-fusibles/royal-ohm/frn02wk0102a10/

author: lowimpedance
author_rank: Super Contributor
timestamp: October 29, 2018, 11:02:56 pm
content: The temp co. is somewhat higher but otherwise should do the job. Certainly cheap enough to try.Just remember to do the cal trim as per the manual, pretty easy stuff but you will need a 'known DMM' to set up a power supply for the correct value, (3.00 V DC and adjust R8), to transfer the cal to the repaired 77.