Fixing A Malfunctioning Keithley Model 179 Digital Multimeter

Inspired by electronics repair videos on YouTube, [Steven Leibson] recently found himself hunting down something to fix on eBay. This ‘something’ ended up being a  certified classic: a Keithley Model 179 digital multimeter from 1978. Listed as non-functional, the unit arrived at his door for less than $50. There weren’t any exciting pops or smoke when he powered it on, but the display seemed to be showing nothing but random nonsense.

The Keithley Model 179 multimeter has a convenient calibration sequence printed on its electrostatic shield cover and a deadly exposed ac line fuse in the upper left part of the photo. (Image credit: Steven Leibson)
The meter has a convenient calibration sequence printed on its electrostatic shield cover and a deadly exposed AC line fuse in the upper left part of the photo.

Ultimately reviving this little piece of history was quite simple, with the main issue turning out to be a dodgy inter-board connector between the main and display boards. After admiring an old repair attempt made on the component, he removed both the male and female connectors, replacing them with new ones.

This uncovered issues with the PCB, as the FR4 material and the traces on it had begun to delaminate, probably due to the old adhesive giving up due to age. With pretty low trace density this wasn’t anything that a bit of care couldn’t work around, fortunately.

Before finding this dodgy connector, [Steven] first tried to clean the front mechanical connectors, which took multiple sessions. This was followed up by oiling the mechanism. With the connector fixed and some cleaning, the meter’s display now read correctly. It still has some issues with starting up though, which [Steven] reckons are due to the old capacitors in the device.

Presumably some recapping will round off this fun device revival experience, but for the time being a Keithley Model 179 has been saved from e-waste, to inspire generations to come.

Digital Microscope With An On-Screen Multimeter

Some things go together, like chocolate and peanut butter. Others are more odd pairings, like bananas and bacon. We aren’t sure which category to put [IMSAI Guy]’s latest find in. He has a microscope with a built-in digital multimeter. You can see the video of the device in operation below.

The microscope itself is one of those unremarkable ten-inch LCD screens with some lights and a USB camera. But it also has jacks for test probes, and the display shows up in the corner of the screen. It is a normal enough digital meter except for the fact that its display is on the screen.

If you had to document test results, this might be just the ticket. If you are probing tiny little SMD parts under the scope, you may find it useful, too, so you don’t have to look away from what you are working on when you want to take a measurement. Although for that, you could probably just have a normal display in the bezel, and it would be just as useful.

At about $180 USD, it’s not exactly an impulse buy. We wonder if we’ll someday see an oscilloscope microscope. That might be something. These cheap microscopes are often just webcams with additional optics. You can do the same thing with your phone. If you don’t need the microscope, but you like the idea, can we interest you in a heads-up meter?

Continue reading “Digital Microscope With An On-Screen Multimeter”

Your Multimeter Might Be Lying To You

Multimeters are indispensable tools when working on electronics. It’s almost impossible to build any but the most basic of circuits without one to test and troubleshoot potential issues, and they make possible a large array of measurement capabilities that are not easily performed otherwise. But when things start getting a little more complex it’s important to know their limitations, specifically around what they will tell you about circuits designed for high frequency. [watersstanton] explains in this video while troubleshooting an antenna circuit for ham radio.

The issue that often confuses people new to radio or other high-frequency projects revolves around the continuity testing function found on most multimeters. While useful for testing wiring and making sure connections are solid, they typically only test using DC. When applying AC to the same circuits, inductors start to offer higher impedance and capacitors lower impedance, up to the point that they become open and short circuits respectively. The same happens to transformers, but can also most antennas which often look like short circuits to ground at DC but can offer just enough impedance at their designed frequency to efficiently resonate and send out radio waves.

This can give some confusing readings, such as when testing to make sure that a RF connector isn’t shorted out after soldering it to a coaxial cable for example. If an antenna is connected to the other side, it’s possible a meter will show a short at DC which might indicate a flaw in the soldering of the connector if the user isn’t mindful of this high-frequency impedance. We actually featured a unique antenna design recently that’s built entirely on a PCB that would show this DC short but behaves surprisingly well when sending out WiFi signals.

Continue reading “Your Multimeter Might Be Lying To You”

On the left, an image of a COB on the multimeter's PCB. On the right, a QFP IC soldered to the spot where a COB used to be, with pieces of magnet wire making connections from the QFP's pins to the PCB tracks.

Epoxy Blob Excised Out Of Broken Multimeter, Replaced With A QFP

The black blobs on cheap PCBs haunt those of us with a habit of taking things apart when they fail. There’s no part number to look up, no pinout to probe, and if magic smoke is released from the epoxy-buried silicon, the entire PCB is toast. That’s why it matters that [Throbscottle] shared his journey of repairing a vintage multimeter whose epoxy-covered single-chip-multimeter ICL7106 heart developed an internal reference fault. When a multimeter’s internal voltage reference goes, the meter naturally becomes useless. Cheaper multimeters, we bin, but this one arguably was worth reviving.

[Throbscottle] doesn’t just show what he accomplished, he also demonstrates exactly how he went through the process, in a way that we can learn to repeat it if ever needed. Instructions on removing the epoxy coating, isolating IC pins from shorting to newly uncovered tracks, matching pinouts between the COB (Chip On Board, the epoxy-covered silicon) and the QFP packages, carefully attaching wires to the board from the QFP’s legs, then checking the connections – he went out of his way to make the trick of this repair accessible to us. The Instructables UI doesn’t make it obvious, but there’s a large number of high-quality pictures for each step, too.

The multimeter measures once again and is back in [Throbscottle]’s arsenal. He’s got a prolific history of sharing his methods with hackers – as far back as 2011, we’ve covered his guide on reverse-engineering PCBs, a skillset that no doubt made this repair possible. This hack, in turn proves to us that, even when facing the void of an epoxy blob, we have a shot at repairing the thing. If you wonder why these black blobs plague all the cheap devices, here’s an intro.

We thank [electronoob] for sharing this with us!

Hacking A New Display Into A Fluke 8050A Multimeter

Old lab equipment was often built to last, and can give decades of service when treated properly. It’s often so loved that when one part fails, it’s considered well worth repairing rather than replacing with something newer. [Michael] did just that, putting in the work to give his Fluke 8050A multimeter a shiny new display.

The Fluke 8050A is a versatile device, capable of measuring voltage, current, and resistance in addition to decibels at various impedences and conductance, too. The original display doesn’t show some of the finer details so well, so [Michael] elected to improve on that when he installed a new 2.2″ graphical LCD to replace the basic 7-segment LCD that originally came with the hardware.

To achieve the install, the original LCD display module was removed from the chassis. A piggyback device that sits under the Fluke’s microcontroller was then used to break out signals for the new graphical LCD without requiring modification to the meter’s PCB itself. An Atmega32u4 microcontroller then takes in these signals, and then drives the graphical LCD accordingly.

It’s a great hack that makes the old multimeter easier to use, and the new white-on-green display is far kinder on the eyes, too. We’ve seen other multimeters get screen transplants before, too. Of course, if you’re new to the world of segmented LCDs and want to learn more about how they work, [Joey Castillo]’s talk from last year’s Remoticon will get you up to speed!

Detailed Big Screen Multimeter Review

It seems like large-screen cheap meters are really catching on. [TheHWcave] does a very detailed review of a KAIWEETS KM601, which is exactly the same as a few dozen other Chinese brands you can get from the usual sources. You can see the review in the video below.

If we learned nothing else from this video, we did learn that you can identify unmarked fuses with a scale. The fuses inside were not marked, so he wanted to know if they appeared to be the right values. We would have been tempted to just blow them under controlled conditions, but we get he didn’t want to destroy the stock fuses until after testing.

Continue reading “Detailed Big Screen Multimeter Review”

Vintage Multimeter Gets An LCD Transplant

Hackers are often of the sentimental type, falling in love with the look and feel of quality old hardware. Of course, sometimes that older hardware needs a little TLC to keep it running in the modern world. [Lex] had a beautiful vintage multimeter that sadly had a broken screen, and set about a nifty repair to restore it to working condition. 

It’s a handsome thing.

The HSN Avometer DA116 is a handsome thing, controlled with two dials and featuring a clean two-tone aesthetic. Even the font on the PCB’s silkscreen is gloriously pretty (can anyone ID that?). However, the original LCD was non-functional. A direct replacement part was sadly unavailable. Instead, to rectify this, [Lex] first hunted down another segmented LCD screen that had the same segment layout.

However, the new screen had a completely different pinout to the original part. Thus, after taking some notes and figuring out what all the pins did, [Lex] whipped up an adapter board to carry the new screen. With some protoboard, some pin headers, and a bunch of point-to-point wiring, the new screen worked just fine, and [Lex] had a functioning vintage meter once again!

The story actually came to us on Twitter, where we invited discussion about the best bodge wiring jobs out there. Feel free to contribute your own stories to the conversation! If you’re in the market for more LCD hacking, be sure to check out the excellent talk [Joey Castillo] gave at the 2021 Remoticon.