Fluke 73 Series I (?) missing fuse but working fine? - Page 1
Forum section: electronics / testgear

author: brandonpaterno
author_rank: Newbie
timestamp: July 16, 2022, 11:39:17 pm
content: Hi, I'm new to the forum. I do a lot of audio stuff and don't really do too many personal projects but sometimes I like to put little electronic things together. Anyways,I came across a Fluke 73 for a dollar at a flea market amidst a bin of assorted things. I decided to get it because before I had a cheapo multimeter which didn't work too well, but did what it needed to do. I opened the fluke to see that there was no fuse present, in fact it looks like some sort of mod has been done by the prior owner. I'm not too familiar with electronics like these multimeters but it seems like there was some sort of trace damage at some point, and that a capacitor (may) have been pulled. The board revision, 7x-3001, was last referenced here:https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/3750/It seems like there should be a red film cap near the metal bar in between the resistors. It also seems like there should be at least one fuse holder/fuse, but I see no evidence of there ever being a fuse in the first place. Attached below is a picture.The funny thing is that the thing works... as far as I know. I'm sure it needs to be calibrated but it gets the same measurements my cheap multimeter gets but this one is *instant!* The only strange thing is that when the meter turns on the display goes grey for a second, turns off for another, and then works fine.Should I just keep using this as is until something frys the thing or should I just use my cheap multimeter? I've never blown a fuse before in my two years of elkectronics work, frankly I didn't know that multimeters had fuses (shows how much I know)Any tips or ideas as to what's going on? Can I add a fuse or is it possible the thing is far too damaged?

author: Martin72
author_rank: Super Contributor
timestamp: July 17, 2022, 12:16:34 am
content: Hi,It looks like the fuses never existed there.And yes, something is missed plus a layer is broken.My hint : Forget about it...

author: retiredcaps
author_rank: Super Contributor
timestamp: July 17, 2022, 02:13:30 am
content: Quote from: brandonpaterno on July 16, 2022, 11:39:17 pmGreat buy for $1. If I found that, I buy that all day long.QuoteJoe has a Fluke 77 which you cannot compare to a Fluke 73. The last digit represents more functionality between the various 70 series models.QuoteYou shouldn't be surprised that the Fluke still works after 35+ years and is probably still within it's calibration parameters. The meter coming on, then going off briefly and then working is normal operation.QuoteHave a look at the yellow circled marks. Those joints look a bit suspicious and may need touching up with a soldering iron?If you show a picture of the front of the Fluke 73, does it say "UNFUSED" (see picture)? If yes, that would explain why there's no fuse holder.Fuses in multimeter are there to protect the meter and user from measuring too much current/amps.edit: UNFUSED pic fromhttps://www.cottandco.com/en/lots/fluke-115-multimeter-fluke-73-multimeter-fluke-77-multimeter

author: mqsaharan
author_rank: Regular Contributor
timestamp: July 17, 2022, 06:31:57 am
content: Nice find.It is zapped but looks very clean. The missing components are spark gaps.The fuse place holders are for 75 and 77 models. Both the fuses are for mA jack.I am attaching here its service manual so you can check, repair and upgrade your meter if you so desire.

author: Fungus
author_rank: Super Contributor
timestamp: July 17, 2022, 08:55:21 am
content: Quote from: retiredcaps on July 17, 2022, 02:13:30 amnb. The PCB trace that's all burnt and blown to hell is on the current shunt. Looks like somebody seriously overloaded it on that ranbe, this is the type of damage that fuses are there to prevent.Does it work on the other ranges?

author: mqsaharan
author_rank: Regular Contributor
timestamp: July 19, 2022, 03:16:35 am
content: The overheated track is not for current measurement function. It is for voltage/resistance functions.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 19, 2022, 09:49:07 am
content: I don't have the 73 but with all the Fluke meters I have the fuse (or fuses) only needed when measuring current.