158 - What is wrong with this Fluke 25?

[@zoeyzhang9866]

Nice repair!

[@arnoldgrubbs2005]

Very nice video! I have a Fluke 25 of my own on my work bench, and I had a 27 at work before I retired. I think both of these are touted as being "intrinsically safe" for use in dangerous conditions ( explosive atmospheres ) as in some industrial plants working with solvents or in mines or the oil production industry.

[@cambridgemart2075]

Interestingly, that is an Australian NSN on the label, I wonder how it ended up half a world away?

[@TheHWcave]

That is interesting. I never checked the NSN. Things to valuable for being thrown away do get around apparently.

[@cambridgemart2075]

@@TheHWcave I think there is a sense of humour somewhere in the department that generates NSNs, UK is -99- and Australia is -66-, or -99- upside down!

[@TheHWcave]

@@cambridgemart2075 I love that!

[@kjamison5951]

What a fascinating video! Thank you for sharing! I saved my overtime and bought a Fluke 175, brand new, that was on offer from RS. I use a 175 at work and it is checked/calibrated annually by the company. I went into to eBay and could not find a Fluke 25 but I did find a Fluke 27 in an auction. It would seem that Flukes hold some value, whatever their age.

[@TheHWcave]

Yes, Flukes hold their value. I also bought a 27 which was broken and fixed it. Will be a future video, Besides the electrical issue, that one had glue residue on the display window which made it hard to read. I tried polishing (for the first time... nothing to lose...) and its like new. Very happy with that one.

[@andersvandegevel8355]

The reason for having two fuses in series is because the big HRC one is expensive to replace, so in most cases just the cheaper one blows. In the rare case of serious breaking capacity being needed, the bigger HRC will save your life.

[@TheHWcave]

Yes that is a possible explanation but call me cynical, I find it strange that Fluke would go to the expense of adding a cheap and an expensive fuse in series just to save the user some money. It may well have turned out that way but I wonder if the real reason behind it wasn't quite that altruistic. I note that in those days other manufacturers did the same with their multimeters. so it could be peer pressure - or a common technical reason?

[@andersvandegevel8355]

@@TheHWcave it's because low current range fuses are expected to die a lot. The low value one is a sacrificial one for common mistakes, the high value one is to save skin and (maybe) circuit when you have a (hopefully) rare large energy mistake. It was quite a common practice on older meters, especially bench ones, not just a Fluke thing. If it was just because they found the low value fuse wasn't sufficient, they'd just replace it with a link when they added the HRC. The reason you don't see it so much any more is to reduce complexity and to make even small mistakes expensively painful. Not sure how much it's used in the latest meters; the newest I have is an Agilent 34401A, which does indeed have a small, relatively low rupture capacity in a rear holder, and a proper HRC fuse in series that you can only get to by removing the cover.

[@josephcote6120]

I have an eBay Fluke 37, which is a 27 in a benchtop case. It worked when I got it although it was listed as parts/not working. A great everyday meter. I do wish the LCD had a backlight.

[@alexwade9921]

I have a Fluke 27 of late 1980’s vintage. It still works very well and I still use it. Probably my favourite meter to use on the bench. Mine has the stand. Regarding the changes you identified between your meter and the schematic for the 27 I think those might just be a matter of age (for either 25 or 27) rather than a difference between 25 and 27. They were probably always manufactured and sold alongside each other. My 27 has three fuses laid out exactly like those on your 25. They’re visible inside the battery bay. I have no need to take it apart so I don’t know about the fusible resistor.

[@TheHWcave]

Yes that makes sense, I guess the 27 I got for comparison is slightly newer and Fluke changed the schematic. Probably there are 25s out there that have only 2 fuses as well.

[@LawpickingLocksmith]

I would say: Do it again so we can see that it is not a Fluke.

[@kjamison5951]

I see what you did there! 😂

[@RBcymru]

Fluke multimeters are good but the newer meters can drift slightly. The older meters do suffer from aging components. Being a calibration engineer I would buy a Fluke 83/85 or 87 but these do suffer from badly designed input terminals. A Fluke 175/177 or 179 is a good meter and if the terminals do come loose you can re-solder them. Drift can be down to over loading the current ranges. Tenma do a multimeter that is 50000 count and similar spec to Fluke 80 series for half the price. DO NOT bother with Isotech, RS Pro or cheaper Tenma meters apart from the mentioned one. Your HP 34401A will drift over time and need a full re-calibration about every 5 tears as DC mV drift, high voltage DC and resistance common errors. You can calibrate a lot of your own equipment using a good 6.5 digit dmm and a TTI counter with annual cal cost about £200 total (£100 each for UKAS calibration). Always get your equipment adjusted if its readings are 50% of the spec this will ensure the meters accuracy.

[@125brat]

Interesting you mention Iso-Tech. I used to be responsible for the compliance testing of those products. Most meters were made by Appa in Taiwan and from the safety side were very good with proper fusing, layout etc for creepage and clearances. Mind you, that was 15 or more years ago when typically the 70 series and the like were new. Things have changed dramatically at RS and the compliance checking is virtually non-existant these days and purely a paperwork exercise. Fluke don't make all their own meters and some are made by Appa, Chung and a couple of others I can't remember now. They are badged by Fluke and many others.

[@cambridgemart2075]

I wonder if the original resistor would have been a Philips part, given that Philips owned Fluke back in the day.

[@arne9219]

Interestingly all my Fluke 27 and 27/FM from that age accept isolated bananas from usual test leads. I also was wondering why you bothered with the 1k value as the absolute value shouldn’t really matter 😅 Apart from that I really enjoyed the video 👍

[@TheHWcave]

Yes, my Fluke 27 (repair coming up soon) has shrouded sockets apart from other improvements like replacing the fusible resistor with a PTC. The resistor value does make a little difference. Say for 50W overload (to ensure it acts 100% as a fuse) the 1K resistor will need 224V but a 2K resistor already 316V. I wanted to stay as close as possible with the original. An alternative would have been upgrading the 25 to a 27 in that area, i.e. adding a PTC. But then I had never worked with fusible resistors before, so I was kind of curious.

[@jp040759]

Good job and repair. What makes a fusible resistor fusible?????

[@TheHWcave]

I think they have a defined (data sheet) and controlled way of failing

[@jp040759]

@@TheHWcave Thanx

[@ssalient]

There is no such thing as having too many multimeters.

[@excavatoree]

I agree.