24 May 2018

Dot matrix LED driver chips

While searching for something else, I came across a forum where a bunch of TIL305 dot-matrix vintage LED displays would be driven by a HT1632C chip. Neat, because it would avoid the abuse of bunch of ATtiny's and allow greater flexibility. Unfortunately the usual Far East sources don't stock a breakout board with the HT1632C already soldered and without a modern LED matrix.

DIY? HT1632C comes in 48/52-pin LQFP package that is too small for my soldering tools.

Well, digging a little further I found that Holtek produces also three versions of the HT16K33 driver, and it is commonly found on breakout boards on eBay, without LEDs attached. It is controlled via I2C and it features a matrix keyboard input too, just in case. Last but not least, its made in 20-28SOP that is manageable with a fine tip soldering iron if I ever want to make a PCB (not a bad idea since wiring is going to be a mess).

I ordered a few, so that all those TIL305 can finally spring to life.

06 May 2018

Industria Macchine Elettroniche IME-141 - power up

A fuse holder inside IME-141
Industria Macchine Elettroniche IME-141 calculator was the one in the lot of four that wouldn't power up, so it was necessary to have a look inside. The first step was to remove three screws and I got a bit worried when I found all of them to be loose. At the first peek inside I noticed the dust (meaning not much has been done inside), the date code on a capacitor telling me (19)73 and a fuse holder: that's a synonym of hope!

Hidden into the fuse holder was this transparent component, showing to the world its inner workings and an obvious gap: the fuse had blown.

Blown old fuse

Its markings suggest it was 125V 1/16A: so large and so sensitive? Perhaps it wasn't even the original one, since there is no marking on the expected value. The closest I could find at home with the same size was 5A, borrowed from another appliance. Well, better 5A and a finger on the power switch than a fully bypassed fuse, isn't it?!

"Hello 2018 World" from IME-141.
All set: calculator switch in "ON" position, finger on the external switch ("OFF"), eyes closed in case something blows up. Click! No alarming sounds, no smells. So I did open my eyes to see the squared 0 staring at me. It works!! Fun is over. HA!

Actually I need to find a safer way to power up the beast without replacing the AC socket. Or forget the historical thingie and fit a standard one.

30 April 2018

A lot of four calculators

This acquisition has been a very lucky find: four devices in the same lot, and three of them from early 1970's! I've had to wait a couple of months before getting my hands on them, but I think it was worth it! Let me briefly introduce them and their display technology (let's not forget I got into calculators because of their displays!):
  • Casio CL-200 co-branded Lagomarsino (Nixie)
  • Industria Macchine Elettroniche IME-141 (Single-digit VFDs)
  • Industria Macchine Elettroniche IME-401 (Panaplex)
  • Canon P34-D (VFD tube)
These devices should provide me with some entertainment, beginning with finding a way to power them up! Only IME-401 has a now-standard AC socket, while larger and older machines need a plug probably called "oval". Nevertheless I have been able to power up three of them with mixed results.

Three 1970's and one 1980's desktop calculators.
The real bounty of this acquisition could be the bunch of apparently unrelated power cords, plugs and sockets that came in the box.

27 April 2018

RD-160: lower part of the tuning range

Before returning the chassis into the Radiomarelli RD-160 case I had to fix the lower tuning range. If it mutes then something stops oscillating. So I probed the variable capacitor with an ohmmeter and found out that the plates shorted in the first third of the range.

A closer look revealed that the outermost plate, that is made of three petals, was bent. And the middle petal was bent inwards, shorting the capacitor.

Last I cleaned up the plates blowing a bit of air and passing a strip of plain paper through all blades.

24 April 2018

RD-160: capacitors replaced

Just a quick visual update now that I have replaced the 5 capacitors. I read an advice of buying axial capacitors as replacements and now I see why.

"All American 5" circuit of RD-160, with new capacitors.

Next step is powering it up!

22 April 2018

Inside the Radiomarelli RD-160

My journey into the wornderful world of valves (tubes) has taken me in front of a 5-tubes radio receiver from 1955: components looked different back then!

Without a wiring diagram I've had to reverse engineer the circuit starting from the tubes. Large-ish cylinders are the possibly leaky capacitors. Two of them have like "melted" their caps: I will replace all five. I am in doubt about the large dual electrolytic, and it will stay for now.

Inside RD-160 - original!
In order to reconstruct the wiring diagram I took a picture of the circuit, cut it on the computer to show only relevant parts, increased brightness and printed it out on A4 paper. This way I can add notes on paper while I understand which component is which. I wanted to print it in B/W, just borders, but it wouldn't be easy to distinguish between components on different layers.

Three out of five "suspect" capacitors have lost their markings. I will chop them off so that their leads will be used as support for replacements. The capacitance meter confirms their expected values, within 20%. Still, I don't trust them.

Now waiting for the order to arrive. I chose replacements rated for 630V and I bought packs of 10, just in case I will step into another valve radio to restore (I want one with the wooden case!).

17 April 2018

Canon Palmtronic 8 (LD-84)

Yes, another calculator showed up at home. This time it is a pocket device called Canon Palmtronic 8, also known as LD-84. It works off 2xAA batteries and has 8 digits shown on a VFD display. It also accepts an external 3Vdc power source.

This one did not need any restoration, except for some light cleaning of the plastic case.

The rightmost digit is slightly fainter than others because obviously it has been "on" longer than other segments.

What else? The weight is just fine, and those two batteries account for lots of it!