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Miscellaneous

A Japanese hot pot: A hot spring without a hot spring

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One of the most famous features of Japan is the availability of hot spring all around the country. If this is an advantage or disadvantage of my new living place in Germany remains yet to be seen, because the hot water close to the surface normally comes along with other earth activity including volcanos and earthquakes… Anyway, I have no source of hot water here other than by gas heating, so at least I wanted to have an outdoor bath resembling Japanese style.

The pot is handmade from high alumina clay, fired at about 1350°C, and shipped from famous Jingdezhen, Jiangxi China, within about 8 weeks. It is a heavy pot, about 350 kg. It resembles the Japanese made bath pots 1:1 but the price is much more competitive and a certain Ms. Wei of the pot company knows how to deal with foreign customers and can manage export of such items as a routine business… Transportation fees in Germany and customs duties, taxes turned out to be more costly than the pot itself.

The essential elements are, (1) the pot, (2) the piping system all made from DN40 glue-fitting PVC-U pipe, (3) a circulation pump (180 Watts, Wiltec 51554, including a filter/strainer), (4) a gas heater (fired by Propan), (5) hot water supply pipe – this is constructed such that it can be drained easily in winter after each use, so it is possible to have a bath also in freezing conditions, made from 18 mm copper pipe and fed by the main hot water system of the house (using natural gas), (6) a regulator system to keep stable temperature.

The water heater has a safety system to switch off the heater after 20 minutes of use, and it has a built-in electric ignition system powered by 2 batteries, 1.5 Volts each. In order to achieve temperature regulation without interfering with the internal circuit of the gas heater, I just switch on and off the 3 V power to the heater.

Normally the heater is only used to keep the water at constant temperature of about 42°C (Japanese baths are really hot…), which takes less than 20 min on-time, anyway, I decided to add a timer circuit that interrupts the heater ever 15 minutes for 30 seconds. So essentially, it can continuously heat the bath even when filling in cold water. Normally the bath is started with reasonably hot water from the house main supply.

Unfortunately, the ignition system by high voltage causes the regulator to hang up. The high voltage sparks change the ground potential it seems, and even some attempts with protection and clean-up circuits (low pass filters) had no permanent effect, when powered from a single supply that is split to 12 V the regulator/timer, and 3 V for the heater. So I now powder the unit from two completely separate powder adapters, and two completely separated circuits, isolated by mechanical relay.

The voltage regulator for 3 V is a simple LM317 circuit, with some more capacitors and features to protect it from any surge voltages.

The temperature regulator and timer, sure you could build it yourself with some microcontroller, display, etc, but no need as the complete module is available for less than 3 EUR mail-order.

The water circuit has the circulation pump. Note that not all the water is passing through the heat, only a certain portion, and pressure is generated by an orifice in parallel with the heater. Temperature sensing is done in the circulation loop. In winter the circulation system can be completely drained and switched-off by appropriate ball valves. So you can still have a bath, but you just can’t heat it by the circulation system (rather need to add more hot water, or just limit the bath to 1 hour or so).

The heat loss seems to be about 1 kW, so we need to run the heater that is using about 1.2-1.4 kg of propane per hour of operation only for some minutes at a time (1 kg propane has about 14 kWh of energy, and we may assume an efficiency of 0.7). Experience shows that is this correct, the heater may switch on every 15-20 minutes of so for about 3 minutes.

Now the system is completely automatic. In normal usage there is no need to adjust any regulators. Just fill in water and switch the bath main switch to “ON”.

Lastly, the water is not just plain tap water but sure enough I am adding bath salts composed such that they resemble my favorite Yamaguchi prefecture hot spring pretty well!

Various

Olympia CD401 Tischrechner: a magnetic keyboard

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This marvelous CD401 Nixie-Tube calculator came to me in pristine condition, from a friend, and including all the accessories and even the original power cord. Just that it has some small defects. Numbers 2 and 7 didn’t work, and some of the keys have mechanical issues. Noteworthy, this little calculator came from Japan, despite being branded Olympia (which is a German company no longer in existence), an made by Matsushita Electrics, also known as Panasonic, in the early 70s. It cost close to 1000 Deutschmarks, may be equivalent to a two week’s salary of an engineer at the time…

Someone had apparently tried to fix it before, using inappropriate tools and scratching some internals, and not taking care of proper alignment of the parts.

The non-reactive “2” could easily be traced by a continuity tester, a bad circuit trace (the grease seems to be slightly acidic and has some greenish discoloration in places – copper corrosion).

The trace would be easily fixed with a short wire and some solder. The other defect – maybe introduced by the earlier repair attempts, a broken reed switch. The keyboard as such is a remarkedly complex setup – each key has several metal and plastic parts, and a magnet that operates a reed switch. Clearly, this had been built to a certain standard of longevity at the time, an engineering tool rather than a “pocket calculator”.

I keep a box of reed switches as spares, so luckly found one that is a pretty exact fit of the original.

Some careful re-assembly, some cleaning of old grease, and the instrument can go for a test. Note that there is exposed mains voltage around the transformer – why didn’t they put some cover?? It is right open and exposed and will give you an electric shock when you touch it…

That’t finally the machine all fixed and in best working order, probably soon it will be 50 years old.

HP 3562A Dynamic Signal Analyzer

HP 3562A Signal Analyzer: a broken display and an easy fix

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Recently, during some phase noise measurements, my 3562A failed. This instrument is an essential part of the noise test set, it is used for all frequency offsets up to 100 kHz, and as a signal/noise source (the 3562A has a fairly capable built-in noise source, signal source, etc.).
While the communication via GPIB went well and I could still complete the test job, the CRT went dark with no sign of life. I also have a second unit, with a LCD display, but the 3562A of the phase noise test set still has its original CRT. Let’s hope we can fix it because I don’t want to invest in a new LCD or anything for this purpose.

So I opened up the box (fortunately, it is accessible on top of the test set which is a stack of instruments, maybe 250 kgs of electronics), and did some checks. As it turns out, one of the rails of the CRT driver boards is down.

Some years back I had already replaced some tantalums, maybe some more of these have gone bad? So I cut some wires at suspicious capacitors – you can normally do this no problem, because the instrument will still function even with some buffer caps missing.

In fact, after the 3rd cut, the rail came back. The tantalum had a full short but no sign of smoke or heat, probably, because of various protection circuits of the power supply.

Replaced it with a similar electrolytic cap, probably this will do. It is a question of repair philosophy, should you replace all tantalums in such device, if you found two defective caps? I decided not to, because the fix every 5 years is easy enough, and there are just too many tantalums in it, moreover, I may break some contacts or cause issues with electrostatic discharge. For the current repair, I didn’t even remove the board, just cut the capacitor from the top and solder the spare back, from the top. As some old laser engineer told me once, the less you touch it, the better it will work. Sure enough, if the objective is to bring the unit back to the best state of reliability, it would be best just to replace the whole CRT by a new LCD assembly, or by a few 100 USD worth of KEMET high-rel tantalums and do a 5 hour solder and disassembly/assembly job…

HP 8569B Spectrum Analyzer

HP 8569A Spectrum Analyzer: two mysterious resistors

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Again, some repairs of a 8569A spectrum analyzer. This time, no problem at all with the front selectors and contacts that break all too often, but with the CRT showing only a defocused vertical line. Some probing around – the analyzer appears to be find but something wrong with the deflection circuit? This is on the A5 assembly, and with no extender board around, quite difficult to probe, and a bit dangerous because this assembly is using +120 VDC. Any short may damage the supply, and any touch may give you a shock. So better exercise some care. By soldering wires, I was able to trace the signal and it seemed to be OK up until to some of the last amplification stages of the X amplifier. Maybe something wrong with the transistors – no these are good. Probing around on the board, checking all values of components close-by: the 75k resistors (fairly large sized 0.5 Watt resistors) are high-resistance, both seemed to have failed at the same time – strange. Eventually, this is becoming a quite frequent failure, already the 5th case or so over the last few years of open high-ohmic, say, 100k and about, resistors that are subject to 100 V or similar “high voltage” usage.

With no suitable 75k resistors available, I went with a combination of 82k parallel to 880k, resulting in 75.01k, close enough. And the 82k resistors that need to carry most of the current are really good old low inductance transistors suitable for such 100 volts service.

The repair, it is not particularly beautiful, but it works and at no cost, with available parts. Finally, some hours of test to make sure there is nothing else at fault in this unit. All good, test passed.

Miscellaneous

Heating energy consumption: first evaluations, and total annual energy demand

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In the meantime, I have collected enough consumption data for gas consumption (mostly heating, some little bits for hot water), and at various temperatures outdoors, including, very cold temperatures.

As it turns out, the gas consumption correlates well with the outside temperature (daily average temperature in 2 m height, as officially recorded close to my place by the weather authorities).

With datasets of daily temperatures for 2019 and 2020, we can then estimate the total gas consumption of these years.

The 2019 predicted consumption:

The 2020 predicted consumption:

For German standards, everything less than 100 kWh per m2 and year is quite reasonable. I need to admit that not all of the rooms are fully heated all the time, but well, it is not all that bad, comfortable, and affordable.

Here an energy rating chart – in German – around 100 is a good value, above 200 … there it is getting really bad, wasteful and expensive!

Generators - Low Frequency

Wavetek 172B Signal Generator: a heavy 00000000

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This Wavetek has been part of an Army sale a while back, and I had used it for some project, but in recent years, it started to gather dust – it is a nice units but pretty heavy and I don’t want to hurt my back.
When I switched it on recently, it showed all “0000000”. The keypad is responsive and a beep sounds with any key pressed, but there is no reaction or output. Sure this can be fixed but I am not a Wavetek expert and all hands full with large gardens and other projects. So I sold the Wavetek to Ulrich Prinz DC3AX who kindly fixed it and shared the repair pictures and details below. Also I have the EPROMs archived in the Manuals Archive in case you need it.

Turns out that the keyboard has an independent processor, but the main CPU board is not initializing properly, normally, it needs to send a string “Wavetek 172B” to the display with self test completed, but the CPU doesn’t do anything.

The sockets on these boards are nowhere near Hewlett Packard quality, but single spring low cost IC sockets that are prone to aging and contact issues. The most critical ones around the PROMs were replace with precision contact IC sockets.

M2114 4k static RAMs, these are known to fail at times, so they were replaced.

Finally, a test, and it boots up and runs through the self test no issues. A marvelous repair because CPU boards can be tricky to fix – let’s hope for long and trouble-free service of the unit at its new owner!

Various

New Smart Home: at least, gas&electric meters are talking to the world wide web

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With the recent move to my new home, some curiosity about the consumption of energy, gas and electricity, first and foremost. The heating system is completely new, so there were no historic data about the annual consumption, and with winter time currently, I thought it could be interesting to collect some data and analyze.

The meters are not the best starting point, the electric meter says, manufactured in Western Berlin, e.g., during the period of separation in Germany, pre 1989… The gas meter is a but more recent but the well known old design.

At least, the gas meter has some provisions for digital read-out, probably, a magnetic system, with relatively coarse resolution, and a mirror “6” which aids itself to optical pick-up with 10 Liter resolution.

Here you can see the mirror… the “o” of the “6”.

To pick up the reflection, I used some IR transmitter-receiver pairs, you may take similar from an used computer mouse, I purchased some sets as surplus parts years back.

Now, the next challenge is to get the readings of the meters from the basement and 2nd floor, to the ground floor office that has the web server – to collect the data in one place and to analyze.
This is achieved by NRL24L10 transmitters in the 2.4 GHz band. These transmit to a common receiver that is connected to the web server (running Apache/Ubuntu) via a wired 9.6 kbaud RS232 link.

The transmitters and receiver are controlled by Atmel m328p, from some ready-to-use Chinese controller boards similar to Arduino nano, but the software and use is all avr-gcc, nothing to do with Arduino.

There is no need to deal with the NRL24L10 chip itself, because there are ready-made small boards available cheaply, less than 1 EUR per piece…

For the gas meter mechanical part, a small piece of plastic scrap and a Nylon screw is all that was needed to get a stable signal.

Sure it needs to be positioned well, but it is not a particularly sensitive or critical adjustment.

First, I just transmitted the strength of the reflected light to the server (receiver), and did all the calculation in the receiver, but this has various issues if the transmission of the signal is interrupted for some reasons, like RF interference or some other outage at the receiver end.

So I decided to change to counting the “6” pulses at the transmitter end, and the transmitter will send data every few seconds (including the time stamp of last counter change, and a time stamp synchronization data package every 10s of seconds).

Now it is counting very reliably, and can recover from receiver outages no problem.

The data received are interpolated to 6-minute intervals, i.e. 240 intervals per day.

With the electric meter, the mechanical part is a bit more difficult, as there is no place to attach a screw or anything, so I decided to use a piece of plastic, precision made to fit the front cover recess, and a metal wire (spring bracket) to hold it in place.

At the right positions, openings have been milled so that the wheel can be “seen” by the IR detector (the wheel has a red mark, and 75 rounds per kWh consumed).

It needed some fine adjustment and tuning of the pick up threshold, and an algorithm to avoid false counting by introducing a dead-time after each pick-up event, because with the wheel turning fast, e.g., when 10 kW are drawn, there have been extra counts. This has now all been eliminated by proper adjustment, more margin of the IR detector.

Some examples, with high power consumption in the workshop, i.e., 5 and 10 kW machinery and heaters in operation.

Additionally, the same system is used to record the living room floor temperature, in a corner, which is a pretty good representation of the heating system’s effect on the house. At nighttime, the heating is essentially stopped (13.5 degC as minimum temperature, which requires no heating unless it is a very cold night). The sensor is a DS18B20, which can be directly connected to the microcontroller with no further converters and delivers good accuracy.

It is seen that the regulation has some on/off characteristics, but the temperature stability seem stable enough for the purpose.

If you want to do similar things or need the code, etc, just drop me a line.

Miscellaneous

Christmas Time: Honigkuchen (honey based cookies)

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It is a long time favorite, and easily stores for some months – honey based cookies. Here is a good recipe.

500 g Honey
125 g Sugar
150 g Water (you may just add some more Honey if you don’t like to add refined sugar, but it makes the dough easier workable)
1 kg wheat flour (can be some coarser type wheat flour)
60-80 g Spice including anise, clove etc., a ready purchased mixture. Adjust quantity to strength of spice and your taste
25 g Ammoniumbicarbonate (“Hirschhornsalz”)
Pottash can also be added, by I didn’t add it, it will make the cookies flat.

First, mix and melt honey, water, sugar, at low heat. Add the other ingredients and work firmly. Let it rest for 2 or 3 days in the fridge (cover to avoid drying out).

Then, prepare cookies, and bake at about 200 degC for 8-10 minutes. These need to be well baked. Underside can be dark brown, but don’t burn them to bitterness.

The Honigkuchen can be stored in a well-closed container for 2 or 3 months no problem.

Various

HP 4140B pA Meter/DC Voltage Source: some incorrect assumptions, but finally, a repair

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Shortly prior to my departure from Japan I started repair of a HP 4140B. A very desirable instrument for semiconductor characterization. The issue remained that output “A” didn’t provide correct voltages, probably due to some issues in the amplifier.
Two month later, I have returned to Germany, and a spare LF256 J-FET opamp had arrived, so I thought it would be a quick fix – but to no avail.

Fitting the LF256 to the board – I usually leave some part of the old wire in the Teflon isolator, because I want to avoid soldering/melting the solder in the Teflon part – it is all difficult to clean up afterwards, so I prefer to solder the new part to some leftover wire, rather than contaminating the isolator.

But- with the new opamp installed, same symptom, no proper output, current limit function of channel A blinking, but the input of the opamp is good. So it must be something else down the chain. Another look at the schematic…

There is an analog switch, followed by a discrete linear amplifier with a dual J-FET input stage.
After some study of the analog switch (cutting a trace and checking it), the switch appears fine. Next in line, the dual J-FET, and in fact, this is dead – found it by measuring the E-B and C-B transition voltages with a diode tester (instrument powdered down and board removed!!), and the transistor around the FET shows largely different values compared to the working B channel. It is 1855-0049 HP part, available in some single piece quantities but expensive!

Looks still shiny and new, but it isn’t working.

Studying some NSN databases, found at least some data of this part, which had been manufactured in equivalent versions by some other manufacturers as well, probably in the 1970s.

It is a rather not so special depletion n-type J-FET. But it is a dual FET part, and while single J-FETs are no problem to get, dual FETs are rare specimens.

Even in their long past days, these didn’t come cheap… maybe something like 40 EUR a piece in today’s money.

So we need to do further study, and there are essentially two kinds of dual FETs – some that have a specially made dual die, with both FETs on one chip and coupled in various ways to keep them from drifting apart with temperature, etc., and the other kind, which is merely just two reasonably matched separate FETs in one case, for convenience more than anything (and for thermal match).

Screening through my inventory I found these 2N5457 FETs which have pretty similar electrical characteristics, in particular, zero-gate-voltage currents.

The parts I have are all quite uniform so there is no need to select a special pair.

With such replacement with similar parts, rather than identical parts, I think it is a good idea to take no risk, so I took the B-channel dual FET and transplanted it to the A channel. And the B channel, which is anyway only a secondary function of the instrument and doesn’t allow the same fast ramps and functions like the A-Channel, it will be definitely good enough to install the two FETs separately (closely together), rather than the original part.

The dual FET of the B channel replaced by two 2N5457.

The B channel dual FET 1855-0049 transplanted to the A channel.

With these repairs, the instrument powdered on just fine, and the output voltages were spot on without any need for alignment. Even the zero bias setting if the LF256, no need to adjust.

Various

Induction range repair – just a couple of IGBTs, and a 20 Amp fuse

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Recently, the induction cook-top of my SMEG range failed, leaving me with potentially expensive repair options quoted at above 1000 EUR, or to do some investigations myself. Surely, the latter option applies in my case. So, after receiving two spare IGBTs by mail, and a high current fuse that matches the “repair option” fuse holder of the cook-top, it took just a bit of soldering to get the thing up and running again.

Mounted the IGBTs, an easy job compared to the tedious mounting of all the coils and cables. It is not quite a service friendly design, and there are many sharp edges that can damage cables and your skin, so better wear gloves and handle everything with care.

After cooking on the range for a while, there is absolutely no problem at all, it’s a 20 dollar fix, if you don’t count your own time – maybe about two or three hours, mostly, to take out the electronics and put them back in.