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122 - Is this Thurlby 1905a 5 1/2 digit multimeter worth repairing? Part 1

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I found this not quite working Thurlby 1905a multimeter on eBay. Its basic functions work but none of the advanced functions because the keyboard is completely dead. To make a replacement keyboard would be a major piece of work and I am not sure if this meter is worth the effort. For now, I constructed a temporary keyboard with the intention that in part 2 this will allow me to get an idea if these advanced functions even work and whether the meter is worth spending any further effort.
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0:00 First test
0:32 The problem
2:29 Repair?
2:56 Fail
3:30 Plan B,C ..
5:48 Temp keyboard build
9:03 Success

Опубликовано:

6 авг 2024

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Комментарии : 30

@colydeane Год назад

A nice bit of ingenuity here, looking forward to part 2.

@cLxJaggy Год назад

I had been having problems with that kind of cable too. I managed to kludge a connection on it by piercing thru it with tiny tin-plated copper wires, heated with soldering iron. That was more a McGyver solution, but worked.

@johncoops6897 Год назад

That smaller keypad layout on the meter looks similar to the size used on Point Of Sale equipment like scales. I think it would be fairly easy to find a smaller membrane assembly to retrofit the existing one. Remember, you don't need anything except the sheets that make up the switches, and you can hack the rest. Also watch EEVblog #1282

@TheHWcave Год назад

Forgot about that episode. Yes that sounds easy but the prices $254 for 5????

@johncoops6897 Год назад

@@TheHWcave - I think that's the whole thing, not just the membrane assembly that you need.

@artursmihelsons415 Год назад

As option there are metal dome switches available. If everything works in that multimeter, maybe, it's worth to create new flex board, using dome switches and order it from PCBWAY, as example.. 😉

@CXensation Год назад

Now you have figured out rows and columns of the switch matrix, you have lots of possibilities to rebuild the front. Forget about any solution incorporating same style of flexible pcb. Instead use a universal pcb layout with a sturdy connection. Try study the services offered by JLCpcb and PCBway for a possible solution.

@plainedgedsaw1694 Год назад

Shielding in that area may not be so important considering the huge hole for display right next to it. What about making a circuit board (printed or just scratched out considering it ain't complex) for smd mount buttons and unsticking keyboard cover, drilling holes and resticking the panel back? How else would you even mount the normal buttons behind it anyway?

@TheHWcave Год назад

I like the idea of a "sandwich" PCB+original panel but the PCB + switches would have to be extremely thin. First there is a groove around the housing, but even if I trim the original front down, the other problem is the mechanical buttons at the bottom. If the sandwich is too thick they can't be pressed in to release. While most are radio-type, i.e. press one in make the other pop out, there are special ones that work differently. But I'll think about it ..

@Wilson84KS Год назад

The first thing I thought of are TTP223 touch modules, you could repeat the keypad matrix on a small pcb and connect the touch modules to it which you place behind the original buttons. I think this is a very cool solution and very easy to do, the hardest part is to find out how the matrix is wired and the result is that you keep the original look but add some modern technology to it, the buttons must not be pressed anymore and will last for much longer, obviously the material it is all made from is not very good, the plastics is drying out and cracking. Another option is to order flex PCB in China, but you never can order only one and it isn't that cheap, to solve this problem again you would have to look for other people who have the same problem and would buy the leftover PCB's, but I'm not sure about the result and how easy or hard it is to do, definitely very time consuming.

@TheHWcave Год назад

Sadly the TTP223 output can't be used in a matrix used by the without additional electronics / microcontroller) to convert the signal. That seems to be true for just about any touch sensor solution. Given the efforts on design and making such a thing or a flex PCB etc, one has to consider whether the meter is worth it.

@Wilson84KS Год назад

@@TheHWcave It can be setup as momentary and toggle switch, is it really not possible to set single modules as momentary NO switches and just use them instead of push buttons, just connecting and disconnecting contacts by using optocouplers or something like that?

@reedreamer9518 Год назад

I remember the era of membrane buttons - what were they thinking? ; )

@TheHWcave Год назад

I think even Thurlby recognised that quickly. I have a few of their only slightly newer kit and none use this kind of keyboard anymore.

@FISHERMAN33RUS Год назад

Good job! Is it mostly a collection thing for you or it is a useful tool at the bench? Investigation process of finding fault and fixing it is really interesting, but what will follow afterwards? For me the tendency of buying such of old equipment is to put it on the shelf for a background, maybe use it 1 or 2 times per year, maybe i am wrong? Didn't mean to offend, just curious.

@TheHWcave Год назад

I do not collect, I want the things to work in my lab. I can't justify the expense of buying new test equipment (exception was my Rigol scope, Brymen 869S and OWON XDM1041). Everything else is used stuff. However, as happens with these things, I now have a (temporary) collection of sorts, in that some are sitting on a shelf / garage waiting for repair & calibration and some have been replaced with other used stuff and I am trying to work out which one to keep and which to sell...

@erikr007 Год назад

If you haven't seen it already this teardown video by Scullcom Hobby Electronics is very good: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-OiKEYsjxbMs.html In the last chapter it briefly discusses the keypad issue and a common approach to fixing it.

@TheHWcave Год назад

Yes, I know Scullcom, watched that video (and most of Louis' other stuff, what a brilliant channel that was. Incidentally my first RU-vid video was inspired by his GPS frequency standard...). Louis also points out that the keyboard cable is indeed the weak point of the 1905a.

@Wilson84KS Год назад

Ouh and about the questions if it is worth it to repair the multimeter, I say it definitely is, I want a desktop multimeter so much, but for me as a hobbyist it isn't worth it to buy one, even the cheapest are extremely expensive just because they have a different shape than usual multimeters, was thinking about to buy a handheld one and build it in a different casing but this thought moved further to an own arduino based multimeter, but for my brain it wasn't enough so it wants to add the transistor tester, a basic function generator and a very basic oscilloscope to it and now a couple of the some others of me are arguing for months about all of this, while my main me says that he doesn't have the programming skills, but they don't care much and say I will have to learn it 😆 Does it look like I am nuts 🤪?

@TheHWcave Год назад

Not nuts but my advise is to start small. Its great to design your own gear and I definitely learned a lot in doing so (including what doesn't work!). On multimeters, the key problem is not so much making one but how to make sure it reads the correct value and how to make it survive the occasional mistake (i.e. wrong range, AC vs DC, volts when Ohm is selected...) we all do these errors occasionally. Calibration of a self-built without a meter to compare to that you can trust is the other problem.

@Wilson84KS Год назад

@@TheHWcave The loudest voice in my head got the Me who asks about the sense and necessity, that is blocking me, I want one but don't really need one. The hardware part is not that hard to make, I got almost everything needed, it is just my brain that refuses to learn the C language properly finally, everything is available as open-source and the adjustment can be put in a settings menu and saved in EEPROM, as I did designing my soldering station with every single variable, also putting it all together is not that hard, but the Transistor Tester code is very complex and I am too bad in programming to implement it.

@asintonic Год назад

Why not try and see if a used or old new stock of the ribbin cable can be found!? 🤷‍♂️

@TheHWcave Год назад

There is no ribbon cable that can be replaced. The cable you see is part of the keyboard itself. I would need to find a 1905a with intact keyboard and swap the whole front panel. I looked but the one I found, the seller would not confirm the state of the keyboard (cue alarm bells going off) and it was too expensive to gamble.

@TheDefpom Год назад

There are places that make custom membrane keyboards, you just design it and they make it for you, at a cost of course.

@TheHWcave Год назад

Yes I agree, but as with all these solutions, is this meter really worth the time / expense? That is essentially the question here. I like a challenge but at the end, the thing must have a good use case. I have many other projects and little time (family and full-time job).

@TheDefpom Год назад

@@TheHWcave yes it isn’t cheap, most of it is setup cost, but someone could do it and get a quantity of them made, and sell replacement’s to those that need them

@TheHWcave Год назад

@@TheDefpom Yes, I agree this is certainly something to consider. I wonder how many 1905As are out there with this problem.

@johncoops6897 Год назад

@@TheHWcave - look at Dave's EEVblog #1282. Remember, you don't need the buttons/front panel, which is the expensive part of the job.