Repair Hacks

634 Articles

Eico Signal Generator Gets A Repair

June 23, 2020 by 5 Comments

The Eico model 377 was a pretty common audio signal generator. [The Radio Mechanic] picked one up from 1956 that was in reasonably good shape, and shares a teardown and repair of the unit that you can see in the video below. The device could produce sine and square waves using a few tubes.

The unit was a bit different inside than expected because there were several versions made that shared the same model number. The bottom of the case had some goo in it, which is never a good sign. Unsurprisingly, the culprit was an old capacitor.

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Repairing A Workhorse Bench Meter

June 18, 2020 by 23 Comments

In today’s market, and expensive high-precision bench meter will have a host of features: graphs, alarms, averaging, and more. It will probably even use an operating system. However, old meters can still get the job done at a price that you can actually afford. A case in point is the Fluke 8842A, solid meters with 5.5 digits of resolution and the ability to do two or four wire resistance measurements.  They are built like tanks and are surprisingly affordable, especially if you consider what they went for when new. [Illya Tsemenko] recently updated a log about repairing such a meter, and there is a lot of good information about them if you own one or are thinking about one.

The biggest problem with repairing these meters is that there are several custom parts including the display that are essentially unavailable. For that reason, [Illya] took a meter with a broken display and used it to source parts for another meter.

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Time Enough At Last: Reviving An Heirloom Typewriter

May 4, 2020 by 28 Comments

You may find yourself living in interesting times. The world we knew two months ago is gone, and there is time enough at last, to finally go through those projects we’ve been putting off for one reason or another. Today, I wanted to explore and possibly repair an old unidentified typewriter that belonged to my late aunt for many decades.

A small disclaimer though, I am not an avid typewriter collector or connoisseur. I enjoy looking at them and using them, but by no stretch of the imagination I want to claim to be an expert in their history or inner workings — I’m a hacker after all. What follows is a layman’s adventure into her first typewriter repair, an exciting tale that explores typewriter anatomy and troubleshooting. Let’s dig in.

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Fixing An Agilent Oscilloscope Power Supply

April 18, 2020 by 22 Comments

We should all be so lucky as [Salvaged circuitry], who scored a cheap Agilent oscilloscope from an online auction. Of course, its low price had a reason behind it, the ‘scope didn’t work. At fault was its power supply, the repair of which was documented in the video below.

These ‘scopes have relatively straightforward 12 V power supplies, extremely similar to off-the-shelf parts. The video is an interesting primer in switch-mode power supply repair, as the obvious failure of the filter capacitor and a MOSFET is traced further to the PSU controller chip. We see a new capacitor mounted proud of the board to reduce the risk of heat damage, and then some careful solder rework to save some lifted pads.

The result, a working oscilloscope. Maybe we’d have hacked in another 12 V supply, but given that this is a piece of test equipment perhaps it’s best to stay as close to the original spec as possible. As a parting shot he shows us an equivalent power supply, and promises us a side-by-side test in a future video.

These ‘scopes aren’t as popular in our circles as the cheaper Rigol range, but it’s worth remembering that they also have a budget model.

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3.2 GHz Vector Signal Generator Tear Down

March 17, 2020 by 15 Comments

[The Signal Path] snagged a fancy Rohde & Schwarz vector signal generator that can go up to 3.2 GHz, but sadly it wasn’t in working order. It powered up and even put out a 1 GHz signal, but the amplitude output was very wrong. Interestingly relative changes to the output were correct, it was just that the absolute output amplitude was off by quite a bit and changed with frequency. That started a detective job which you can follow along in the video below.

The instrument is pretty high-end, and did not report any problems even during self-check. This implied that all the internals were probably good and whatever was wrong probably lay close to the output. The service manual’s block diagram wasn’t terribly useful, especially given that all the processing portions appear to work well.

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Dissecting China-Sourced Vintage HP 1970s ICs: Genuine Or Not?

March 16, 2020 by 10 Comments

While repairing a real-time clock module for a 1970s HP computer that had been damaged by its leaky internal battery, [CuriousMarc] began to suspect that maybe the replacement clock chips which he had sourced from a seller in China were the reason why the module still wasn’t working after the repairs. This led him down the only obvious path: to decap and inspect both the failed original Ti chip and the replacement chip.

The IC in question is the Texas Instruments AC5948N (along with the AC5954N on other boards), which originally saw use in LED watches in the 1970s. HP used this IC in its RTC module, despite it never having been sold publicly. This makes it even more remarkable that a Chinese seller had the parts in stock. As some comments on the YouTube video mention, back then there wasn’t as much secrecy around designs, and it’s possible someone walked out of the factory with one of the masks for this chip.

Whether true or not, as the video (also included after the break) shows, both the original 1970s chip and the China-sourced one look identical. Are they original stock, or later produced from masks that made their way to Asia? We’ll probably never know for sure, but it does provide an exciting opportunity for folk who try to repair vintage equipment.

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Plastic Cleanup Via Retrobrighting

March 13, 2020 by 31 Comments

If you work on old radios, electronics is only one of the skills you need. The other is wood or metal working to restore the cabinets and chassis. However, more recent electronics have plastic and old plastic tends to turn yellow. [Odd Experiments] shows how to whiten plastic using a UV light source, aluminum foil, and hydrogen peroxide. Generally, ABS is the plastic at fault, especially those mixed with bromine as a fire retardant. You can see the results in the video below.

Note the peroxide in use was 12% — much stronger than what’s probably in your medicine cabinet. That’s usually only 3% solution, although you can get different strengths including some over 30% if you shop. However, if you search you’ll find that people have used 12%, 6%, and even 3% successfully, although we’d imagine it takes more time with 3%.

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