Repair and Calibration of Valhalla Programmable Precision Standard

Precision standards are the pinnacle of test and measuring instrumentation. Well engineered, sure, but also beautifully built and a feast to look at, no matter how old they are. [Shahriar] at “The Signal Path” often gives us the skinny on such equipment. In the latest episode, we get a look inside a Valhalla 2701C Programmable Precision DC Voltage Standard.

Even by 1990 standards, it is a fairly basic instrument, capable of producing just DC Voltages from 100nV up to 1200V. But it is a reference standard, so the output is highly stable, accurate and precise.  He snagged it from eBay on the cheap but transport seemed to have caused some damage. It would switch on and relays would click when he pressed buttons, but the 7-segment LED display was blank. Luckily, opening the top cover fixes that problem – just a loose connection between the front display and the main board. Examination also shows that adding a 120mA DC current range would require adding additional components on the main board so his hope of doing a quick firmware upgrade is short lived.

[Shahriar] takes the opportunity to walk us through the various sections of the well built unit. It’s apparently seen some repairs during it’s life. A few capacitors look changed, and a relay housing has seen damage from a soldering iron. The digital section is mainly the 6800 micro controller, an EPROM and a NVRAM, and it generates the PWM signals needed for producing the output voltages. A highly precise reference signal is essential for such equipment, and this one uses the LM299 with a “custom” suffix meaning it was specially screened and binned. He does a quick calibration run, but it’s obviously rushed and doesn’t produce stable results. But that could also be due to the low quality cables he used, or a number of other factors. Calibrating such equipment is a job demanding both time and patience.

While this may not knock your socks off. For that, check out this post where [Shahriar] does a tear down of the one million dollar Labmaster 10-100zi Oscilloscope, or this other one where he plays around with a half a million dollar oscilloscope you’ll probably never use, much less own.

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Fixing Broken Monitors By Shining A Flashlight

[dyril] over on the EEVblog has a broken LED TV. It’s a fairly standard Samsung TV from 2012 that unfortunately had a little bit of corrosion on the flexible circuit boards thanks to excessive humidity. One day, [dyril] turned on his TV and found about one-third of the screen was glitchy. After [dyril] took the TV apart, an extremely strange fix was found: shining a light on the corroded flexible circuit board fixed the TV.

The fix, obviously, was to solder a USB light to a power rail on the TV and hot glue the light so it shines on the offending circuit. Solving a problem is one thing, though, understanding why you’ve solved the problem is another thing entirely. [dyril] has no idea why this fix works, and it’s doubtful anyone can give him a complete explanation.

The TV is fixed, and although you can’t argue with results, there is a burning question: how on Earth does shining a light on a broken circuit board fix a TV? Speculation on the EEVblog thread seems to have settled on something similar to the photonic reset of the Raspberry Pi 2. In the Raspberry Pi 2, a small chip scale package (CSP) used in the power supply section would fail when exposed to light. This reset the Pi, and turned out to be a very educational introduction to photons and energy levels for thousands of people with a Pi.

The best guess from the EEVblog is that a chip on the offending board handles a differential signal going to the flex circuit. This chip is sensitive to light, and shutting it down with photons allows the other half of the differential signal to take over. It’s a hand-wavy explanation, but then again this is a very, very weird problem.

You can check out [dyril]’s video demonstration of the problem and solution below. Thanks [Rasz] for sending this one in.

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Continuing Education via Wheel Balancing

There’s an old saying that you should make things twice. Once to figure out how to build the thing, and again to build it the right way. [Pmbrunelle] must agree. His senior project in college was a machine to balance wheels. It was good enough for him to graduate, but he wanted it to be even better.

The original machine required observation of measurements on an oscilloscope and manual calculations. [Pmbrunelle] added an AVR micro, a better motor drive, and made a host of other improvements. As you can see in the video below, the machine works, but [Pmbrunelle] still wasn’t happy.

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Rehabbing an Historic Tool from Champion Blower and Forge Co.

Here’s a tale that warms our hearts. [Gord] is helping out the local living-history museum by rehabbing a historic woodworking tool that they want to add to their live demo woodshop. It’s a hundred-year-old manual drill press that has seen a ton of use.

acme-rod-tig-repairThere are three things that [Gord] has going for him. First off, the Champion Blower and Forge Co. built them to last. Second, he’s not really working on a deadline; the museum doesn’t need it back until May. And third, [Gord] has the tools he needs to do this right.

After cleaning and blasting [Gord] gets down to the really interesting repairs. First off, it wouldn’t be a drill press if someone hadn’t tried to drill through the table at some point. TIG welding filled it up and some milling brought it back. This same method was used again to make a beautiful custom replacement ACME rod. Throwing in a custom bushing replacement, turned wooden handle, and a several other fabricated parts, and [Gord] had the press working again. Check out the mechanism in the video below that shows the crank action turns the bit and a cam advances it through the work piece.

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Desoldering Doesn’t Necessarily Suck

What’s your favorite way to fix soldering mistakes or get usable components off that board you found in a Dumpster? I’ve always been partial to desoldering braid, though I’ve started to come around on the vacuum pump depending on the situation. [Proto G] sent in an Instructable that outlines nine different ways to desolder components that take varying amounts of time and skill.

He starts with one that is often overlooked if you don’t have a solder pot. [Proto G] recommends this method only when you don’t want to keep the board. Cover the solder joints of the components you want to keep with flux and hold it over the solder pot while pulling out the components with pliers. The flux isn’t critical, but it makes removal faster and easier.

For boards in need of repair, [Proto G] uses a manual pump or copper desoldering braid that comes coated with flux. If you can afford one, a desoldering machine seems like the way to go—it combines the heat of a soldering iron with the vacuum of a manual pump. Desoldering tweezers and hot air rework stations look like great ways to remove surface mount components.

If you enjoyed this, check out [Bil Herd’s] guide on component desoldering. There are also few ways that [Proto G] doesn’t mention, like holding the board over an alcohol flame. Let us know your favorite desoldering method in the comments.

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Fail of the Week – Steam Cleaner fix goes bad

[Sven337] was gifted a steam cleaner, and seemed pretty happy because it helped clean the floor better than a regular mop. Until it fell one day, and promptly stopped working. It would produce steam for a short while and then start spitting out cold water, flooding the floor.

Like any self-respecting hacker, he rolled up his sleeves and set about trying to fix it. The most-likely suspect looked like the thermostat — it would switch off and then wouldn’t switch on again until the water temperature fell way below the target, letting out liquid water instead of steam after the first switching cycle. A replacement thermostat was ordered out via eBay.

Meanwhile, he decided to try out his hypothesis by shorting out the thermostat contacts. That’s when things went south. The heater worked, and got over-heated due to the missing thermostat. The over-temperature fuse in the heater coil blew, so [Sven337] avoided burning down his house. But now, he had to replace the fuse as well as the thermostat.

[Sven337] bundled up all the parts and put them in cold storage. The thermostat arrived after almost 2 months. When it was time to put it all together, a piece of fibreglass tubing that slides over the heater coil was missing. Without the protective sleeve, the heater coil was shorting out with the grounded heater body, blowing out the fuses in his apartment.

That’s when [Sven337] called it a day and threw out the darn steam mop — a few dollars down the drain, a few hours lost, but at least he learnt a few things. Murphy’s Law being what it is, he found the missing insulation sleeve right after he’d thrown it away.

Listen Up: iPhone Hack Diagnoses HVAC

We all know that guy (or, in some cases, we are that guy) that can listen to a car running and say something like, “Yep. Needs a lifter adjustment.” A startup company named Augury aims to replace that skill with an iPhone app.

Aimed at commercial installations, a technician places a magnetic sensor to the body of the machine in question. The sensor connects to a custom box called an Auguscope that collects vibration and ultrasonic data and forwards it via the iPhone to a back end server for analysis. Moving the sensor can even allow the back end to determine the location of the fault in some cases. The comparison data the back end uses includes reference data on similar machines as well as historical data about the machine in question.

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