CRT Cataract Surgery

Back in the good old days, people got their information by staring into particle accelerators that could implode at any moment, and we liked it that way, by gum! To protect against disaster, CRT monitors were equipped with a safety screen laminated to the front of the tube. Decades of use often resulted in degradation of the glue used to hold the safety glass on, leading to the dread disease of “CRT cataracts.”

Luckily for aficionados of vintage terminals, [John Sutley] has come up with a cure for CRT cataracts. The video below shows the straightforward but still somewhat fussy process from start to finish. You’ll want to follow [John]’s advice on discharging the high-voltage flyback section of any stored charge; we speak from painful experience on this. With the CRT removed from the case, removing the safety screen is as simple as melting the glue with a hot air gun and applying gentle leverage with a putty knife. We’d think a plastic tool would be less likely to scratch the glass, but [John] managed to get them apart without incident. Acetone and elbow grease cleaned off the old glue, and the restored CRT looks great when reassembled.

With its cataracts cured, [John] says his next step is to restore the wonky keyboard on his Lear Siegler ADM-3A terminal. Perhaps he should look over this VT220 keyboard repair for ideas.

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Eye Tube Tests Capacitors

Most component testers require removal of a component to test it. [Mr Carlson] recently restored an old Paco C-25 in-circuit capacitor tester. He does a very complete video tearing it down and showing how it works and why.

The tester uses an eye tube (sometimes called a magic eye tube) as an indicator. A 40 MHz oscillator produces a signal that finds open and shorted capacitors. You can also measure resistance, although you have to wonder how accurate it would be in circuit. If you want to read the original manual, there are a few copies online.

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Dual Trace Scope 1939 Style

If you buy a serious scope these days, it is a good bet it will have at least two channels. There is a lot of value to being able to see two signals in relation to one another at one time. Even though the dual-trace oscilloscope goes back to 1938, they were uncommon and expensive for many years. [Mr. Carlson] found a device from 1939 that would turn a single channel scope into a dual trace scope. In 1939, that was quite the engineering feat.

Today, a dual trace scope is very likely to be digital. But some analog scopes used CRTs with multiple beams to actually draw two traces on the same screen. Most, however, would draw either one trace followed by the other (alternate mode) or rapidly switch between channels (chopper mode). This Sylvania type 104 electronic switch looks like it takes the alternate approach, switching between signals on each sweep using vacuum tubes. You can see the device in action in the video, below.

The inputs and outputs of the device are just simple binding posts, but the unit looked to be in good shape except for the power cord. [Mr. Carlson] does a teardown and he even traced out a hand-drawn schematic. Fair warning. The video is pretty long. If you want to get right to the switch actually driving a scope, that’s at about one hour and seven minutes in.

We doubt we’ll see a tube-based Quake game anytime soon. If you want to get into restoring old tube-based gear yourself, you could do worse than read about radio restoration.

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Retro-Styled Raspberry Pi Radio

Ok, so you want a radio — but not just any radio. It has to be wireless, access a variety of music services, and must have a vintage aesthetic that belies its modern innards. Oh, and a tiny screen that displays album art, because that’s always awesome. This 1938 Emerson AX212-inspired radio delivers.

Building on the backbone of a Raspberry Pi Zero W and an Adafruit MAX 98357 mono amp chip, the crux of this single-speaker radio is the program Mopidy. Mopidy is a music player that enables streaming from multiple services, with the stipulation that you have a premium Spotify account. Once signed up, [Tinkernut] helpfully outlines how to set up Mopidy to run automatically once the Pi boots up. The addition of a screen to display album art adds flair to the design,  and Adafruit’s 1.8″ TFT LCD screen is small enough to fit the bill.

But wait — there’s more!

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Adding Character To The C64

The venerable Commodore 64, is there anything it can’t do? Like many 1980s computer platforms, direct access to memory and peripherals makes hacking easy and fun. In particular, you’ll find serial & parallel ports are ripe for experimentation, but the Commodore has its expansion/cartridge port, too, and [Frank Buss] decided to hook it up to a two-line character LCD.

Using the expansion port for this duty is a little unconventional. Unlike the parallel port, the expansion port doesn’t have a stable output, as such. The port contains the data lines of the 6510 CPU and thus updates whenever RAM is read or written to, rather then updating in a controlled fashion like a parallel port does. However, [Frank] found a way around this – the IO1 and IO2 lines go low when certain areas of memory are written to. By combining these with latch circuitry, it’s possible to gain up to 16 parallel output lines – more than enough to drive a simple HD44780 display! It’s a testament to the flexibility of 74-series logic.
It’s all built on a C64 cartridge proto-board of [Frank]’s own design, and effort was made to ensure the LCD works with BASIC for easy experimentation. It’s a tidy mod that could easily be built into a nice enclosure and perhaps used as the basis for an 8-bit automation project. Someone’s gotta top that Amiga 2000 running the school district HVAC, after all!

Restoring a Japanese Oscilloscope

Oscilloscopes have come a long way. Today’s scope is more likely to look like a tablet than an old tube-based instrument. Still, there’s something about looking into a glowing green tube, especially if you’ve done the work to resurrect that old hollow state device. [NFM] picked up a Kikusui OP-31C–a vintage Japanese scope at a second-hand store. He made a video of his restoration efforts that you can see below.

The scope actually powered up and worked the first time. Of course, unlike a modern scope, the OP-31C has to warm up before it will show up. However, the pots needed cleaning and as a precaution, he replaced the old oil and electrolytic capacitors.

The big transformer and the coarse-looking single sided circuit board certainly will bring back memories if you are old enough. [NFM] had a schematic of the scope and takes you on a tour of the innards, although his schematic had some subtle differences from the actual unit, possibly due to some repair work.

He was going to rebuild one of the large electrolytic “can” capacitors to keep the outer shell with newer (and smaller) modern capacitors. However, he found a very similar modern capacitor and used that, instead.

We think it would have been more fun if the scope didn’t work. However, it was still a great tear down of the old tube-based device. This is a bigger device than the last old scope tear down we looked at. Not that we haven’t seen smaller ones (although, the link in the post has moved).

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Command Alexa With a Completely Mechanical Vintage Remote Control

Anyone with grandparents already knows that in ye olden days, televisions did not have remote control. Your parents probably still complain about how, as children, they were forced to physically walk over to the TV in order to switch between the three available channels. In these modern times of technological wonder, we have voice control, programmable touch screen remotes, and streaming services that will automatically play an entire season of the show you’re binge watching. However, before these, and before the ubiquitous infrared remote, television manufacturers were experimenting with ways to keep kids from having to run across the living room every time the channel needed to be changed.

Early remote controls were simply wired affairs — nothing too surprising there. But, it wasn’t long before methods of wireless control were being introduced. One early effort called the Flashmatic would shine light onto a photoelectric cell on the television set to control it. Of course, it might also be controlled by unintended light sources, and users had to have good aim to hit the sensor. These issues soon led to the introduction of the Zenith Space Command remote control, which used ultrasonic frequencies to control the TV.

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