Category: Restore

Recently, my father wanted to give away his complete photo equipment, which had accumulated over the last 50 years. Fortunately, I could still intervene in time and now some dings of it will remain a little longer in the family. “Complete photo equipment” sounds like a lot of stuff now, but it was just a not quite full jute shopping bag with three cameras, as many flashes, all kinds of lenses, two light meters, extension rings, etc. pp. Everything is in a state of disrepair after a long time of use and needs some attention.

First I chose something simple and went for one of the three flash units, an “Elgawa N128”.

Very important for all who want to get old devices out again and put them into operation: NEVER simply turn on an old unit that has not been in use for 10-20 years or more. Almost certainly the filter electrolytic capacitor in the power supply will be degenerated and lead to a short circuit. In other words, after a short time the electrolytic capacitor will go bye-bye with a bang and there will be a lot of work for the restorer. Of course, this applies primarily to devices with a mains connection.

So I opened the device first.

The inner workings are clearly arranged with few components.

Most of the components are from 1983, the flash itself from 17.5.1984.

I have desoldered and reformed the electrolytic capacitor. I have dedicated a separate article to the topic of restoring and reforming electrolytic capacitors. Here only so much to the topic: Without voltage the oxide layer in the electrolytic capacitor slowly degrades. The process is reversible as long as an electric field is applied again. Since the rebuilding of the oxide layer is an electrochemical process, it takes some time. I do this with a short circuit proof high voltage power supply and control the leakage current through the electrolytic capacitor while gradually increasing the voltage. After a few hours or days, the electrolytic capacitor is ready to go again. In this case, it only took about 4 hours for the leakage current to settle below 400µA at nominal voltage of 350V, an excellent value.

In the meantime, I took a closer look at the circuit board. Obviously it was a misproduction, which was corrected manually. A conductor was drilled out and a wire bridge was installed. Nowadays this would be electrical scrap. Another interesting thing is the fuse. Between the two solder joints on the lower left, a very thin wire is installed as a fuse. This is cheap, but unfortunately very sensitive to touch. I promptly broke the wire while cleaning it and had to extend it on one side with a small piece and solder it back on.

I have also drawn the circuit diagram while waiting for the newly formed electrolytic capacitor, for the interested electronics engineer. I find it interesting that the exposed trigger contacts are directly connected to the mains voltage via two 2.2 Megohm resistors, i.e. without galvanic isolation. This would certainly be solved differently today.

After reassembly at the end, everything worked wonderfully again. The flash is far more powerful than anything built into cameras. The decent sized capacitor is discharged through the flash tube with no current limit. This gives a real bang every time, which I still remember from my childhood and easily illuminates rooms up to 9m away. The 180 ohm / 5 watt series resistor has to cope with just under 300W for a short time during charging and then always gives off a tiny wisp of smoke. This is not threatening and overall the device is quite robust with the disadvantage that it always has to be charged at a power outlet after every single flash.

Update 24.05.2023

The latter disadvantage could be circumvented with an additional device, the inverter BZG1, which was also produced by VEB Elgawa Plauen (Vogtl.). This portable device generated 220V from 4 mono cells to charge the flash. A kind reader sent me the circuit diagram taken from an original, many thanks for that.

BZG1_Transverter_02

Quelle: Christian Seifert

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In older devices, for example measurement technology, one often finds cable harnesses tied by hand. This refers to a number of wires that are knotted together with so-called binder twine to form a stable structure. This type of wiring has to be done manually and is therefore very time-consuming. For this reason, it is essentially only used in the aerospace industry today. There are various other ways of producing wire harnesses, such as with cable ties or hoses, etc. But this article is only about the original method with twine. I can imagine that the first wire harnesses were made for telephone exchanges. In any case, the builders of analog switching technology were true masters at crunching wires together.

Basically, cable harnesses have several advantages.

• The cables are more stable when tied together.
• Less space is needed for the cabling.
• Errors during assembly or maintenance are avoided.
• Overall, the result is very good fail-safety.

Recently, I restored an old oscilloscope and had to add the missing harnesses again. That was the reason why I dealt with this topic in more detail. Here in the picture you can see the first result and I am overall satisfied with it.

First condition to tie a harness yourself is the right twine. In the past this was a waxed thin natural yarn, probably jute, sisal or flax. In very old telephone switching equipment from the late 20’s or 30’s, which I cannibalized as a kid, you can still find such yarn. Nowadays the material is something like dental floss with a lot of wax. There are only a few suppliers left who supply end users with it. SEGOR-electronics GmbH from Berlin carries it in its assortment under the name “Abbindegarn“. As “Abbindeschur” I bought my supply at Bürklin Elektronik. I also strongly recommend to use a binding twine explicitly made for wire harnesses. Other materials do not work as well and may not be stable over time.

I came across an alternative variant that I still like: durable yarn, probably star twine is dipped in hot beeswax.

Now the art of knotting is still missing. For an easy start I recommend to follow the guidelines of the FAA, the “United States Federal Aviation Administration”. This has published in its “Advisory Circular” 43.13-1B, Chapter 11 “Aircraft Electrical Systems” instructions that contain only two variants of tying and are so simple and clear.

Quelle: FAA AC 43.13-1B, Chapter 11

Another tip: You can build up the wiring harness in at least two dimensions on a board with small nails. To do this, hammer in a small nail at each bend and at each branch. The wires can then be bent along there, then tied. If the shape of the tree goes into the third dimension, it becomes more difficult and I would wire and bind it directly in the device.

At mikrocontroller.net you can find a thread which also deals with this topic. From this thread come the following multiple variants for node binding. In the end you have to decide for one variant. I decided like this:

• Initial knot: “Form A mit Sicherheitsknoten”
• Intermediate knot: “Form B für glatte Oberflächen”
• Final knot: “Durchschlungener Schlussknoten”

Grundknoten, Quelle: www.mikrocontroller.net
/attachment/49981/Blatt412_Grundknoten.png

Verlängerungsknoten, Quelle: www.mikrocontroller.net
/attachment/49982/Blatt413_Verlaengerungsknoten.png

Anfangsknoten, Quelle: www.mikrocontroller.net
/attachment/49983/Blatt414_Anfangsknoten.png

Zwischenknoten, Quelle: www.mikrocontroller.net
/attachment/49984/Blatt415_Zwischenknoten.png

Schlussknoten, Quelle: www.mikrocontroller.net
/attachment/49985/Blatt416_Schlussknoten.png

Knotenbund, Quelle: www.mikrocontroller.net
/attachment/49986/Blatt418_Knotenbund.png

The full thread is here: https://www.mikrocontroller.net/topic/64283

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