17 November 2017

Linear PSU failing with overvoltage

According to timestamps on components, I have owned this linear power supply for 30 years (rms K135). It powered my first CB station (Midland Alan 48) and who remembers how many other devices. Lately it has been powering a 12V LED strip in the shack-lab.

One of these days I wanted to take a picture of a multimeter (will be feature on the blog, don't worry) and I needed both something to measure and less light in the shack. So I unplugged the LED strip and wired the PSU to the multimeter.

To my great surprise I read 24V. What?! That would have burned the LED strip and everything else I had connected in the meantime. But, with the LED strip powered, it behaved as expected and outputted 12V or so. Of course I cross-checked the reading with several DVMs and they all agreeed.

A bad capacitor? I opened up the PSU and I was greeted by a large amount of dust. And two 78S12 in parallel, as I remembered. Hard to remove the dust, but once components were in the clear, I still had 24V out without a proper load.


Capacitors looked OK. No leaks, no deformation. Unwillingly I reached for the solder side of the PCB and disconnected one 78S12 at a time (just the output pin, lazy me). One regulated at 12.5V, the second at 24V. Well, it didn't regulate at all then!

I temporarily replaced the bad one with a 7812 and the output is still 12.8V.

So, watch out for this simple technology too! Until today I would test the Amps rating of a PSU. Now I will check the open circuit voltage!

07 November 2017

My first HF RTX, in 2017

Got home a bit early tonight from work and didn't want to stare at a screen, so I finally dug out my first HF transceiver for a quick check-up.

It is an Icom IC-728, 100W on HF bands, AM/CW/SSB, triple conversion receiver. I think I bought it in 1993 after the high-school graduation. The price was a bit less than 1'000'000 lire (that's about 820€ in 2017's value).

First I did a visual inspection of the circuits for leaking capacitors: no signs. Then I grabbed the DC power cord from the IC706 and powered it up. It was exactly as I remembered it when it was last used .... 20 years ago or so. Whew!

I reached for the coax that enters my little shack and inserted the hot pole into the antenna socket. At last HF noise filled my room!! Why just the hot end? Because there's no antenna on the other end! It's a coax left over from my balcony experiments 9-10 years ago (seek blog archives if you want). But it does provide few metres of pseudo-antenna. Just don't press the PTT.

I quickly tuned around the bands. I found CW stations on 40m (and I could even make sense out of it!), some AM broadcastings too.

I caught myself few times looking for a "MENU" button, but this radio has no menu: each key has one function (some have two). That's it. All functions are one press away.

Then I wanted to reduce the incoming noise from the open line antenna and ... no DSP, of course! All you get is a Noise Blanker and Pass-Band Tuning: neither of them is effective against modern QRM. Well, I "retuned" my ears and it was fine.

I love the smooth effect of the large tuning knob. I could keep tuning for hours.

I will do my best to put it on the air even if propagation doesn't seem to be helping.

(I didn't take a picture. I will next time I take it out of the box ... hopefully soon!)

29 October 2017

Failing old LCD displays

Following my recent interest in old numeric display technologies I came across old calculators, and started collecting them. In early 1970's there was a lot going on in the research of display technologies, so while Nixies were fading out, VFDs taking their place where there could be a lot of environmental light, LEDs and LCDs were entering the market.

Overheating causes early LED displays to fail faster, especially if run at full brightness.

Sharp EL-5103S
Early LCDs on the other hand lost the "vacuum" inside and became unusable. You can see the failure as a darkened area in the corners/border and there's nothing you can do.

But I wouldn't expect this kind of failure from my Sharp calculator made in late 1980's or the VHF transceiver of early 1990's! Unfortunately replacing an LCD is not easy and you can hardly fit a replacement in the same space. So these devices just turned into (my personal) museum pieces.


The upper area of the display shows signs of air leak.


Too bad for the scientific calculator that served me in high school and at the university. But it looks like a modern replacement costs less than 10€! And I will look for some old battery powered pocket calculator as well, possibly with LED display.

24 October 2017

Old instruments with a warm glow

With the purchase of the Philips PM6645 frequency counter I double the number of instruments sporting Nixies as display device in my lab.

Here they are, the PM2422 Multimeter and the PM6645 Counter both from Philips:

Philips PM2422 (left), Philips PM6645 (right).
I think the multimeter is slightly older than the counter, because the darker front panel looks more 1960's to me. It has a red-coated glass, while the 6645 has clear glass and clear tubes. Both devices are huge compared to today's standards, even if inside there is a lot of room. Probably back then workbench space was not an issue, maybe not an important cost in companies budgets?

Both Philips instruments sit on my oscilloscope, a Tektronix 7000 series, also from 1970's.

Why not add two more nixies in the picture with my biNixie clock?




19 October 2017

New toy: 500 MHz Philips frequency counter

At the Mercatino by ARI Biella in October 2017 my Nixie-radar noticed a frequency counter with as many as 9 tubes. It is a Philips PM6645 500 MHz device, with excellent sensitivity and 10 MHz OCXO reference. Considering that I had a 100 MHz kit-built counter, given the price and the specs I couldn't let it on the table.

At 80€ the beauty came home with me, an early Xmas present:


It mounts common ZM1005 Nixies. It is built with still commonly available parts in case something breaks

17 October 2017

Keeping jump wires in order during maintenance

I think this tip fits the "tribal knowledge" section launched at GQRP reflector and printed in SPRAT magazine.


There are some times when a lazy builder has used jump wires and pin headers to join two boards, rather than fitting proper block connectors. The situation is depicted in the picture below.


Then maintenance time comes, you don't remember neither the wiring scheme nor where the documentation is ...

So, you need to remove a bunch of jump wires but keep knowledge of their order. You have an easy option: take a picture and let them loose. Unfortunately they don't come in many colors, and some colors can be easily mixed up. And the simple idea kicks in: transfer one side of the jump wires on a free piece of pin headers so that they stay in the same color order but can be moved out of the way. The picture helps nevertheless, but order and wire bends will be preserved.

Now ... time to do some shopping for block connectors in various sizes!

10 September 2017

Redraw Analog Meter scale with Inkscape

A dual-needle clock.
Guess what? I've had a challenging idea of a (clock) project, and it has suddenly become top priority. Because of the new challenge.

I want to make a clock using a dual needle analog meter. Ideally an SWR meter would be converted into this analog clock. Electronically speaking, with an Arduino and a couple of PWM outputs, interfacing is simple. A few lines of code and you're done.

The challenge lies in redrawing meter scales. The easy part requires to scan the original panel detached from the meter, and then it is all a learning expeerience.


Once you compute that the needle moves over an angle of 60 degrees with a radius of about 48 mm, both scales have to be drawn with proper marks: one every hour or five minutes.

Old fashioned way: draw it by hand. Fun and relaxing, but not too professional looking.

Test printout.
Do it on the computer: how? A drawing software is needed. Possibly free. And with layers so that the original scan can be used as a reference. Something in the back of my mind suggests that I need a vector graphic software and the search engine response is: Inkscape. It runs on Windows, Mac and Linux.
Not willing to install software for a one-time project on "main" home computers, I turn to the 10-year old HP Pavillon laptop on which I installed Ubuntu Linux 12.04. Once I head to the package manager and search for Inkspace I am welcomed with a warm "Already Installed" message.
The Internet is full of tutorials, but Inkscape itself is well documented too. In two hours I manage to redraw my scales the way I want and I even get the size right at the first printout. All for free.
The original scale (on plastic) vs. redrawn.
By the way, the laptop is a Core2Duo with 1.5 GB RAM and 120 GB HDD (dv6236ea Frankenstein). It runs LibreOffice just right. Firefox surfs the Internet without a problem and I can watch HD videos full screen off YouTube because the NVIDIA graphic card is fully supported. Arduino IDE works too and ... Dropbox (which does not work anymore on WinXP)!