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

September 25, 2022 by Arya Voronova 17 Comments

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!

TRS-80 Model II Lives Again

September 17, 2022 by Al Williams 15 Comments

A lot of people had a Radio Shack TRS-80 Model I. This was a “home computer” built into a keyboard that needed an external monitor or TV set. Later, Radio Shack would update the computer to a model III which was a popular “all in one” option with a monitor and even space for — gasp — floppy disks. But the Model II was not nearly as common. The reason? It was aimed at businesses and priced accordingly. [Adrian] got a Model II that was in terrible shape and has been bringing it back to life. You can see the video of how he’s done with it, below.

The Model II was similar to the older “Trash 80” which had been used — to Radio Shack’s surprise — quite often by businesses. But it had more sophisticated features including a 4MHz CPU — blistering speed for those days. It also had an 80×25 text display and a 500K 8-inch floppy drive. There were also serial and printer ports standard.

There were a few interesting features. The floppy drive’s spindle ran on AC power and if the computer was on, the disk was spinning. In addition, there was bank switching so you could go beyond 64K and also you didn’t have to share your running memory with the video display. In theory, the machine could go beyond 64K since half the memory was bank switchable. In practice, the early models didn’t have enough expansion space to handle more than 64K physically.

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Troubleshooting Barcodes: A Lesson In Critical Thinking

September 8, 2022 by Al Williams 26 Comments

We’ve all been there. Something that is known to work doesn’t work out in the field. But back at home base, it works fine. How do you fix it? Of course, there’s no one right answer to that question, but [Benji York] had a particularly satisfying round of troubleshooting some errant barcodes and even came up with a very creative solution.

Here’s the setup: a customer couldn’t read some barcodes sent from [Benji’s] company. Yet when the bad barcodes returned, they were fine. They looked fine, too. In a Twitter post, [Benji] challenges you to see if you can tell what’s wrong.

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Small Engine Failure Leads To Impromptu Teardown

September 1, 2022 by Tom Nardi 20 Comments

When the 6.5 HP (212 cc) Harbor Freight Predator engine in his kid’s go-kart gave up the ghost after some particularly hard driving, [HowToLou] figured it would be a good time to poke around inside the low-cost powerplant for our viewing pleasure. As a bonus, he even got it up and running again.

For an engine that has a retail price of just $160 USD, we’ve got to admit, the inside of the Predator doesn’t look too shabby. Admittedly, [HowToLou] determined that the cause of the failure was a blown connecting rod, but he also mentions that somebody had previously removed the engine’s governor, allowing it to rev up far beyond the nominal maximum of 3,600 RPM. No word on who snuck in there and yanked the governor out, but we’re betting it wasn’t the 7-year old driver…

Replacing the connecting rod meant taking most of the engine apart, but for our education, [HowToLou] decided to take it a bit further and remove everything from the engine. After stripping it down to the block, he re-installs each piece while explaining its function. If you’ve ever wanted to see what makes one of these little engines tick, or perhaps you’ve got a Predator 212 cc in need of a repair or rebuild, the presentation is a fantastic resource.

Incidentally, this isn’t the first time we’ve seen the go-kart in question — back in June, we covered the unique electric reverse that [HowToLou] came up with for it.

A multimeter connected to the EEPROM chip with crocodile clips, showing that there's a 0.652V diode drop between GND and one of the IO pins

Dead EPROM Dumped With Help Of Body Diodes

August 26, 2022 by Arya Voronova 10 Comments

[Jason P], evidently an enjoyer of old reliable laser printing tech, spilled a drink (nitter) onto his Panasonic KX-P5400 SideWriter. After cleanup, everything worked fine — except that the PSU’s 5 V became 6.5 V during the accident, and the EPROM with LocalTalk interface firmware died, connection between VCC and GND seemingly interrupted inside the chip. Understandably, [Jason] went on Twitter, admitted the error of his ways, and sheepishly asked around for EPROM dumps.

Instead, [Manawyrm] wondered — would the chip have anti-ESD body diodes from GND to IO pins, by any chance? A diode mode multimeter check confirmed, yes! It was time for an outlandish attempt to recover the firmware. [Manawyrm] proposed that [Jason] connect all output pins but one to 5 V, powering the EPROM through the internal VCC-connected body diodes – reading the contents one bit at a time and then, combining eight dumps into a single image.

After preparing a TL866 setup, one hour of work and some PHP scripting later, the operation was a success. Apparently, in certain kinds of cases, dead ROM chips might still tell their tales! It’s not quite clear what happened here. The bond wires looked fine, so who knows where the connection got interrupted – but we can’t deny the success of the recovery operation! Need a primer on dumping EPROMs that are not dead? Here you go.

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Frequency Counter Restoration Impeded By Kittens

August 24, 2022 by Al Williams 12 Comments

We think of digital displays as something you see on relatively modern gear. But some old gear had things like nixies or numitrons to get cool-looking retro digital displays. The HP 521A frequency counter, though, uses four columns of ten discrete neon bulbs to make a decidedly low-tech but effective digital display. [Usagi Electric] has been restoring one of these for some time, but there was a gap between the second and third videos as his workshop became a kitten nursery. You can see the last video below.

In previous videos, he had most of the device working, but there were still some odd behavior. This video shows the final steps to success. One thing that was interesting is that since each of the four columns are identical, it was possible to compare readings from one decade to another.

However, in the end, it turned out that the neon bulbs were highly corroded, and replacing all the neon bulbs made things work better. However, the self-check that should read the 60 Hz line frequency was reading 72 Hz, so it needed a realignment. But that was relatively easy with a pot accessible from the back panel. If you want to see more details about the repair, be sure to check out the earlier videos.

We love this old gear and how clever designers did so much with what we consider so little. We hate to encourage your potential addiction, but we’ve given advice on how to acquire old gear before. If you want to see what was possible before WS2812 panels, you could build this neon bulb contraption.

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Drastic Plastic: Enclosure Rebuild Uses Donor Material

August 21, 2022 by Kristina Panos 10 Comments

Although 3D printers are great, people tend to use them as a universal hammer wherein almost everything becomes a nail that’s just begging to be struck. So as hacker appetites become finicky with the same old fare, it’s refreshing to see an enclosure restoration done in such an old-school fashion. To wit: [Doidão Santos]’ classic repair of the crumbling side fairings on a vintage amplifier.

Yes, instead of designing replacement pieces, printing them, and hiding the layered evidence with paint or an acetone blur, [Doidão] called upon a broken sound system whose chassis bore a relief in the corners similar to that of the amplifier.

After cutting out two matched pieces of donated plastic, [Doidão] taped them together and welded ’em with a soldering iron outfitted with a curved-but-flattened spade tip that looks ideal for this purpose. Although the donor enclosure provided much-needed relief, one corner was lacking in this aesthetic, so [Doidão] cast a little bit of molten plastic using the relief as a mold.

Once the pieces were tacked together, [Doidão] filed them down, sanded them, polished them to a nice shine, and installed them on the amplifier. They look great, and no one will be the wiser. But if we were in [Doidão]’s shoes, we’d tell everyone what we’d done. Be sure to check it out after the break.

Ready for more fantastic plastic resto-hacks? Let us introduce you to [drygol].

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