All posts by Simon

CNC Tools

Tool Grinding Machine Saacke UW II NC: a few basic repairs

Leave a comment

The next big task, moving the Saacke from the entrance area of my house, to the workshop building. Fortunately, there are no stairs and steps, essentially, flat ground, but moving a large 300 kg electric cabinet, and a 700 kg machine, it is no easy task if you don’t have the right tools

Eventually, with the help of a friend and a pallet jack, maneuvered it to the location, but getting the pallet our from underneath a the machine, difficult. In a large factory, you just lift it up by crane of forklift, pull out the pallet, and let it down slowly. Also, you could build a tripod or gantry, and use a hoist to lift it up, but it is all pretty dangerous and labor-intensive, because I don’t keep all kinds of structural steel here.

Eventually, I managed to tilt the machine enough with a small hydraulic car jack, put two heavy flat steel bars underneath (70×15 mm), and lifted it up on some wooden support alongside the pallet, just suspended about 5 mm above. This way, I could pull out the pallet, and then lower the machine done bit by bit, by tilting it, and lowering the support 1.5 cm at a time, to avoid undue tilting. Take care that the whole thing doesn’t shift, and keep you fingers and feet clear at all times!!!

Eventually, after about 2 hours, the machine is at its final place. I will probably screw it down with three bolts, so it won’t move after setting it exactly (I mean very exactly) level. It makes it much easier to work on an exactly level machine, because you can use an electronic level to adjust angles pretty accurately. The seller did take great care of packaging the cables and plugs, glad these were not damaged in transit, because fixing these plugs normally means to completely newly wiring them, and while they are still widely available, these industrial plugs don’t come cheap.

Now, to some basic repairs, to fix the damages inflicted on the machine during transport.

First thing, a wheel of the electric cabinet (which has 3 doors, so to open the doors, you need to move around the cabinet. One wheel completely broke, probably someone hit it onto some wall when loading the truck. Rather than buying 4 all new wheels for such old machine, I try to fix what I can from stock I have, rather than buying ready-made parts. After all, that’s one of the purposes to have a workshop rather than a warehouse full of spare parts.

I cut-off a piece of a 35 year old rod of polyamide that I had around since my childhood time, once found at a scrapyard… then some machining on the lathe, and, a very study wheel is ready and mounted!

The fan of the table (X axis) drive, it really got damaged severely, fortunately, except some wire damage, the motor cover prevented further damage to the drive system, coupling, and, the very expensive ball screw that drives the table.

Most of these fans have their connectors at the outside, but the original one had been cabled to the inside of the cover. At least, I found a good replacement fan 112 m3/h nominal air capacity, run directly from 230 VAC mains.

Some disassembly of the connector, to get the wires exposed, some drilling.

Some soldering, shrink tubing has glue inside.

Still some need to adjust the cooling covers, but finally, got all the cables mounted and fiddled through. Also removed a few spoons full of grinding dust, and other dust.

Both the X and A (rotary) axis drives have new coolers.

Looking good, but the drives don’t even get that hot.

Next thing up for repair, the cover of the table.

Really terribly bent, taking it off was no easy task, drilling out one of the screws and taking great care not to damage the table.

To straighten it out, it took some patience, a vice, a polymer hammer, some pieces of wood.

Bending carefully, hammering it with quite some force, it is no thin metal but a pretty solid sheet. Amazing how crudely the carrier handled the shipment.

Some more knocking and bending.

Eventually, cleaned the plate and mounting surfaces with engine cleaner, still having some old cans around, but ordinary petroleum also works, and doesn’t attack plastic.

One great addition to the machine – a very nice German-made adjustable high-precision grinding vice, gifted to me by a relative. The vice has some little rust, but I will give it a good polish before using it on the grinding machine.

CNC Tools

Tool Grinding Machine SAACKE UW II NC: “the small one” arrived

Leave a comment

Over the last several month the electronic workshop has suffered from little work with test equipment repair, I think, we have an economic crisis – nobody seems to be interested in keeping their old equipment going, if even the new equipment is idle. More time to spend with traveling and other tasks, including, finally getting a new tool grinder.

For the fabrication of microwave components, like, mechanical filters, test antennas, etc., I am using custom-made tools of HSS (high speed cutting steel), mostly the parts are made of brass of Ni-Cu(-Zn) alloys, so HSS tools are superior for precision machining, compared to, for example carbide tools that don’t hold a sharp edge well.

Usually, we are considering small cutters here, 6, 8, 12 mm diameters. A radius tool, for example, for internal turning or single-edge milling.

…precise angles must be kept to keep the cutting edge going.

Also, for very tiny pieces, with complicated internal features, single point cutters don’t work well, so I need to resort to strong, custom made step cutters. Note that the shapes are calculated according to electric requirements, but the practical fabrication needs tests and adjustments, and eventually, repeatability, to get good results. Otherwise, the parts will randomly scatter in performance and it is hard to make a set of, for example, 3 pieces, without making 10 pieces scrap, with all the wasted time for machining and, especially, testing.

These tools can be cut by hand on a so-called cutter grinder, earlier introduced by Deckel company of Munich, model “SO”, but now available as import from China, at quite reasonable quality and cost (still, about EUR 1000).

While this little marvel is working very well, it demands outmost focus and consideration when grinding cutters, and is very time consuming to use. Re-grinding tools reproducibly takes practically the same effort than just making a new tool – all angles have to be set again, and all at the same risk of error and misoperation.

In effect, I have been using tools even when a little bit blunt, at a loss of surface quality, burrs (which are extremely bad, because we cannot polish these electric precision parts without destroying the precision, and burrs do show up in refection coefficients and gains).

A solution – we need to get computers and controls involved, in short, CNC. Buying a good CNC tool grinder, 4 axis to also be able to cut and re-sharpen gear cutters or mill cutters, will set you back at least 100 kEUR, including various expensive software options and difficulty in keeping it going without a service contract.

So I have been shopping around for a more affordable option – buying a solid heavy mechanical machine suitable for retrofit (for example, adding a new motion controller – using LinuxCNC on my other machines, fixing some electronics, replacing some or all of the drives and axis motors; but using all the existing mechanical system, the existing grinding spindle, etc.). This search has been underway since last year August, and after finding a machine, even paying, the seller damaged it so badly in his warehouse that he returned the money, still, no machine for me. Eventually, I found this very interesting machine, Made in Germany in the 80s, based on one of the best and solid designs of a manual machine, the SAACKE UW II. The main features are (hardened) roll-bearing supported long table with ball screw, tapered roller bearing A axis (heavy enough for milling), and prismatic cross-slide (trapezoidal screw) on wide-spaced support, along with a 1 mm-per-turn Z adjustment (high precision worm gear).

The introduction of the machine, considered by SAACKE as “the SMALL one”, no less than 80000 DM in 1985… probably equivalent to 90 kEUR today.

The 1 kW spindle is by far enough for the purpose, the machine can also cut very large milling cutters, flat grinding and round grinding (also tapered grinding) is all easily possible because of the 900×140 mm table.

Having found the machine at a reputable dealer in December 2023, it took several month until I could actually buy it, eventually, got it for very reasonable money, just about 2 EUR per kg, shipment included!

It arrived on two pallets, well secured and packaged. But with some parts sticking out. Already in phone conversation with the seller we had the concern of damage, but there was no practical way to transport it here at reasonable effort, rather than just giving it to a commercial carrier on pallets. Surely, I would always suggest you have your machines point-to-point delivered, even drive the truck yourself.

The transport took more than a week, and the carrier probably loaded and unloaded it several times from the truck, eventually, inflicting various damages to the machine. Fortunately, they didn’t drop it altogether.

A broken fan, a completely broken and ripped-off side plate, a broken roller, etc.

Quite some effort to disassemble the parts, find replacements, etc. – commercially, hard to fix, but we are talking about a major retrofit and modification anyway, so we can do it step-by-step in the evening and on (rainy) weekends, not counting all the hours.

One great plus of this machines are the full manuals, even of the motor drivers (using Berger Lahr 51117/50 stepper motors, really big ones!). For some control boards, and the PEP computer (the old brain of this machine), at least connection diagrams.

The main electrics of this machine, very nicely made in a general control cabinet, with all high quality contactors and fuses.

The cabling and connectors are all of the highest quality, costly, heavy duty German-made design.

The old control boards, in a nice rack. I am planning to use the existing motors for the table and A axis, the cross-slide and Z (which has one shared driver), haven’t made a decision yet, will just get it working for test reasons I believe.

The feed of cross-slide and Z is done by a feed control system rather than the 2-axis control (table X and rotary A axis that is controlled by the computer, coordinated motion to cut spiral flute cutters).

Soon will power it up. Just a note – this machine didn’t have ground connected, but wired as PEN connection, with a N-PE bridge. So it needed some testing of isolation (which it easily passed), and has already grounded 220 VAC and 24 VDC control voltages (adjusted the tap to get the voltages down a bit – design for 220 V, but I am getting about 230-233 VAC here). So if you get into such adventures with old machines, please make sure to contact someone knowledgeable about electric systems, don’t just plug it in!

Next up will by a study of the motors and drivers, some cleaning, some tests of the mechanics (have some precision granite square here to check for any wear/perpendicularity, and a high precision encoder to check the A axis).

Miscellaneous

A good “Springerle” recipe

Leave a comment

A good recipe for “Springerle”, a traditional German Xmas cookie, there are many around but this time I took precise records to ensure consistent results.

My intention was to make somewhat smaller Springerle quickly, and the key point is a slight anis smell, some anis seeds, and nicely developed “foot” of each cookie.

The results turned out very well, and in the meantime, all have been consumed.

The “foot” is clearly visible, so are the anis seeds.

The recipe is adapted from an old book, a famous general cooking book of Ms. Paula Horn, but it is lacking some precise measures and temperatures.

Apart from the recipe, you will also need a roller, similar to this one.

250 g of Eggs, (weight includes the shell)
500 g of powdered sugar

Combine and beat it very thoroughly to a creamy mass.

Mix in 500 g of freshly sifted flour, mixed with 3 g of powdered anis, and 1 g of sodium bicarbonate dissolved in about 10 mL of warm water.

Rest the dough for 30 minutes, then roll it to about 1 cm thickness. Don’t add too much flour when rolling.

Then uniformly push in the carved roller to leave impressions. Cut to rectangular pieces and put them on a non-stick paper, lightly sprinkled with anis seeds. Keep these 18-24 hours at room temperature so that the cookies dry, on an flat surface, so the cookies won’t deform.

Then bake without touching the cookies first, 18 minutes at 150°C upper/lower heat should be just fine. The final cookies were about 8 mm thick, before baking. Thicker cookies may take longer, just ensure that they stay white, only the edges can turn very lightly brown. Don’t worry about the ammonia smell.

Once they come out of the oven, they may still be a little soft, don’t touch them yet.

After letting them rest for 2 weeks, they should be pretty hard, but delicious.

Various

NE555 Watchdog Timer: the ESP32 needs some oversight

6 Comments

The readily available ESP32-DevKitC boards have served me well in many application, but there are some issues with one of the circuits that is up all throughout the year in my house to record moisture and temperature levels. Occasionally, like, every few month, this ESP32 gets stuck, so the web server running on that ESP32 is not responding anymore, and the logging of the data will stop (red marked portions in the plot).

The root cause of that relates to the current pulses drawn by the WLAN circuits of the ESP32, and despite connecting a good USB power supply, proper cables, and capacitors, it seems that there are occasional issues that I haven’t been able to solve be capacitors, better power supply, or software restart-features. I added the later, but the ESP32 freezes to a level that any software reset triggered by the code won’t work. Shortly disabling the power converter on the ESP32-DevKitC (of the on-board 3.3 V regulator – its EN/enable pin is pulled high by a resistor) will restore the function and get the circuit started again.

As I am not always around watching this circuit, I added a good old trusted NE555 timer, which will send a reset pulse (by pulling the EN signal low through a Schottky diode), and the capacitor is shorted by the small MOSFET, as long as the ESP32 is sending a pulse (this is send every 10 seconds approximately, for a few milliseconds) — if the ESP32 gets stuck, there won’t be any pulses, and the NE555 will then reboot the ESP32 every other minute by cycling the power to the ESP32.

Miscellaneous

A new Honigkuchen recipe

Leave a comment

A new recipe for delicious christmas cookies, called, “Honigkuchen”, say, honey cookies:

Prepare a mixure of 250 g wheat flour, 100 g rye wholegrain flower, 15 g christmas spices (anis, cinnamon, etc.), add,

300 g of honey – heat so that it is fully liquid but don’t boil

2.5 g potash (potassium carbonate), 5 g hirschhornsalz (ammonium bicarbonate) – dissolve these salts in about 10 mL of warm water (don’t worry if it doesn’t all full dissolve), add to the mixture.

Mix and kneed to a thorough dough, let it rest about 2 days at room temperature, well covered.

For cookies about 8 mm thick, then bake at 175°C for 15 minutes.

For a glossy surface you can paint them with condensed milk before baking.

Earlier recipe, here: Christmas Time: Honigkuchen (honey based cookies)

Miscellaneous

Bauhaus VoltoLux LED Lamp: a early failure sickness finally subsided

Leave a comment

Some of the ceilings in my house have LED lights installed in false ceilings, a total of 45 led lamps of the same kind (GU10, 4 Watt reflector LEDs). These are of regular quality, sourced from Bauhaus, a normally trustworthy outlet. But certainly these LED lights cannot be trusted at all. Of the 45 pieces installed, already 4 failed in the first year – occasional use. And another one just failed recently.

The advantages claimed are various, long lifetime, rugged, etc., but Bauhaus doesn’t say that you need to buy 10% more lamps than you need, just to replace the early failing lights. Not even to mention about the effort or replacement, etc.

All of the LEDs are 25360318 with frosted front, 10 LED chips per piece. The failure mode is normally intermittent, so the LED will come on for a little, then go off, it may also come on after a little while, unpredictable.

As it turns out, these LEDs are actually repairable, but removing the front glass disc (frosted diffusor), which is done by heating it for a little while with hot air at about 200°C. The front disc seems to have fixed with some epoxy glue.

Poking around, it becomes clear that the failure more is a broken interface between one of the LED chips, and the aluminum heat-conducting round board they have been soldered to. So, either the design has some flaw, or there are thermal issues or solder/flux issues when manufacturing. Shock or vibration effects can be excluded, because these lights have ever since the renovation been mounted in the ceiling, with no touch or vibration.

To fix it, I just re-flowed the solder, after applying a little flux, and the issue went away. Now you can close the light again, using epoxy glue, and it may provide some further service. No statistics yet on the lifetime of repaired LEDs.

In any case, buyer beware of any of the praised LED lamps, many may fail on you well before their expected lifetime ends, better keep all receipts, so that you can have them replaced by the Bauhaus hardware store, or wherever you prefer to buy your lighting supplies.

LCR Meters

HP 4192A LF Impedance Analyzer: another visit to the workshop

Leave a comment

The analyzer, I had fixed it 3.5 years back, see HP 4192A LF Impedance Analyer, the instrument has been back to very good shape, and since then been operated at an university overseas. Recently, I got the message that repair is needed, the instrument didn’t start up.

I tried hard to fix it remotely, because of the significant size and shipment cost, and the general risk of shipping such precision gear around the world. But to no avail, the failure seemed to complex to repair by remote instructions.

First difficulty, to get the instrument shipped to Germany, and to get it through customs – quite a task that took several hours, personal appearance at the customs office, and some paperwork, along with a small fee.

Following the old rule, to check the powers supply first, it was quickly seen that there is a short on the -15 rail, and systematically unplugging the assemblies, quickly found the short on the A3 assembly plug, which is also powering the A1 assembly – the location of the actual fault.

Smell and eye are the best methods… to find easy faults.

Once you know the location, easily seen – the burned inductor. I replaced it by a 4.7 µH inductor I had around, and fitted a new capacitor (tantalum cap).

The NEC-branded cap was dead-short.

Now, the instrument powered up, at least the power supply, but no further sign of life. Checked around the CPU board, and strangely, even the first test showed, no clock! the CPU clock is derived from the A3 master oscillator, by a divider chain – and probing there, no signal on the 1 MHZ or 100 kHz lines either.

The diver chain uses various divide-by-2, 74C74 flip-flops.

Hard to see, but to determine the defective chip, I cut the clock pin at the 74C74, because the clock was low. So I was not sure if the clock generator/amplifier was defective, or just overloaded by the 74C74.

With no 74S74 (guaranteed to run at 75 MHz, typically up to 115 MHz clock) at hand, I replaced it by a 74F74 (which easily handles the 40 MHz clock).

Interestingly, both 74S74 (HP part 1820-0693) had failed. Maybe both were suffering from some transient when the power supply sorted. We may never find out.

Finally, I noticed some unreliable switch-on characteristics that could be traced to some flaky resistors on the power supply board – this board had corrosion issues that damaged some resistors.

A little box of replaced parts… not too many.

Finally, put the instrument to a 24 hours tests, and also run some calibration of DC bias, which had drifted a little. Otherwise all well in spec and well tuned.

Packing it all up: this time, a package to Saudi-Arabia. The instrument wrapped in bubble wrap, then a layer of styrofoam, then a wooded box re-inforced with metal parts and screws, and a cardboard layer all around (without cardboard, DHL will rank it as “special handling”, at a significant additional charge).

After about 2 weeks, the instrument safely arrived in Saudi, and it is indeed working again. Recipient is happy, me too!

Miscellaneous

Metalworking: strange defects of long-used tools

Leave a comment

Recently, I found two strange defects in my workshop, noteworthy to write it down.

Ever since I expanded my workshop I notices some losses of compressed air, i.e., when coming back after a business trip, the pressure of the compressed air pipework is down from normally 6.5 bars, to only 2-3 bars, or even less after a longer vacation. I had attributed it to some leaking air gun or something like that, but finally I did a search and found various leaks at one distribution point.

(1) the water mist filter had a leak at the drain valve — fixed it by closing it altogether. There is not too much water collected, it is installed only to avoid dust and such getting into the system further downstream.
(2) one of the fitting was leaking, because strangely there are some air fittings available that neither have a seal surface, nor conical thread, to it is hard to get it tight by tread tape in the first place (sometime I resorted to gluing-in those fittings with Epoxy glue).
(3) Still, when checking with some soapy water – bubbles at the distribution fitting (5 connections 1/2″). Strange, strange, strange.

Clearly, a defective casting with a hairline crack leak. Maybe the temperatures or the mold or the liquid brass were not right, or the pouring wasn’t steady enough.

The defect line goes all around the fitting, otherwise I would have tried to file it out and solder it tight. Anyway, it is not worthwhile to fix such part at the risk of it failing again. So I replaced it with a new fitting at the cost of EUR 9.90 and at least 3 hours of work to get it all investigated, replaced, fitted and leak tested. Maybe a good idea to fully upgrade the pressurized air system of my workshop, which is now a combination of various distribution pieces, hoses, connectors. But there are trade-offs of perfection, cost, and efficiency — I have actually installed some air pressure distribution pipes for others (like, polyamide pipe, PE-Al composite pipe), but at my own workshop, I will be dealing with a less perfect system, at least, the major leaks have now been found and eliminated.

Another instance of strange failures, I noticed some problems with a bench vice, the smaller size vice I use regularly, and have been using since my childhood. If I remember right, I bought it for something like 35 Deutschmarks way back around ~1990. After all these years, it had some failures, the spindle pin sheared off once (maybe because I tightened it too much), and also a retaining piece of the front part of the spindle wore out (probably very soft steel and insufficient lubrication). Also some part of the casting broke off before, circled in black. Now, I almost injured myself as a part came loose unexpectedly, finally, as they say, always check the tool before you use it.

Didn’t need to go far, a major crack of the dovetail guideway.

It is cracked through, but holding on enough so that the defect is not easily seen without disassembly.

Finally, a cast iron bench vice, after 33 years of service (not always careful use), it may eventually break.

For replacement, I wanted a slightly bigger bench vice, 115 mm width. Also, a solid steel vice that is not too bulky and has a strong grip. These don’t come cheap, but I found a good (but rusty) Peddinghaus Matador steel vice for 35 EUR used, listed in online adds.

After some cleaning, adjustment, and other TLC, it is installed on the bench and working great. Definitely a step up.

Various

Meridian 506 CD Player: after 5 years, in need for more attention

2 Comments

Recently, I had two instances of equipment coming back after some year – with different defects that at their first visit in my workshop. One device is the Meridian 506, a high-class CD player that is popular with hifi enthusiasts, and has been marketed for many years in various different versions. Earlier I had fixed some design issues with the motor driver of the CD deck, see Meridian 506 CD Player: a hot driver.

This time, it wouldn’t detect any CDs, and made some noises. The deck was still opening fine. After looking around, there is no obvious defect, the power supplies are good. All the service modes work – just that I can’t get it read discs or even lock on tracks, it just spins up, then stops.

Reading through all various posts, it seems clearly related to the CD head assembly, this version of the 506 uses a CDM 4/19 Philips laser head assembly, and these are known to wear out over time, i.e., the laser will show aging, and then the mechanism can’t lock on the CD.

Well, easy enough, I found a CD 480 player cheaply as used goods, and this has the desired CDM 4/19.

It arrived strangely packed, but well, better strangely packed than insufficiently packed. Indeed, a lot of styrofoam, chips and paper inside.

Inside, a very simple assembly, much lighter than the Meridian deck. Just some thin plastic.

Easily disassembled the donor.

There are some changes necessary – the hub is different, but can be removed with simple tools (plastic tools) and switched.

Well, all this done, unfortunately —– no success. Still same symptoms. Next, poking around the main TDA chip, there are no signals that are of any use. Strange. Normally it should at least start reading and locking, but it doesn’t (not that the CD drive uses a feedback loop to keep the head on the track, by adjusting the laser arm coil current according the the laser feedback; in these drives, the laser arm is driven by a coil).

After some further study, finally realized that the CD is spinning the wrong way. How can that be? Seems like a defective motor driver! On the small board of the CD deck, there are two L272, and one of them is terribly hot. Not good.

The L272 has long been obsolete, but I would two pieces cheaply on a Chinese website, these were apparently no new but recovered from used equipment. Well, no problem, I rather buy used parts than fake parts.

With these repairs done (not easy because the soldering of the L272 is very strong, need to put a lot of heat to the small board because all the ground pins are firmly connected to a ground plane), the Meridian is working great again, let it play for several hours with no skipping.

And, we now still have a spare laser head assembly should it fail next.

Microwave, Micro-Tel 1295 Precision Attenuation Measurement Receiver (2nd unit)

Another Micro-Tel 1295 Precision Attenuation Measurement Receiver: irresistible green

3 Comments

I am trying hard to resist the temptation of buying more test equipment, but the Micro-tel special green color has a hypnotic effect on me, and combined with the right price, I could not resist to buy one more Micro-tel 1295 receiver. These are very capable 0.01~40 GHz fundamental-mixing receiver (fundamental mixer until 18 GHz, above that, harmonic mixer), with very large range, like, 120 dB, and 0.001 dB attenuation resolution. Ideally suited to calibrate attenuators or to check antennas, etc.

The unit – offered as non-working – arrived very well packed. Unfortunately, many people send sensitive equipment in some thin cardboard boxes. This particular equipment cost close to 85 kEUR in 1989, plus mixers. Also, it has long been under export control from the US, because of its unique range and accuracy.

Bubble wrap, other fibre wrap inside.

Finally all in foil.

The defect, it doesn’t show any reading on the display, and both the HI and LO leds are on, which is abnormal. The 1295 has a 12 dB range bolometer detector, any signal below 0.5 dB or above 12.5 dB will light up the LO or HI lamp, and you would need to select another 10 dB step of the IF attenuator (a high precision 30 MHz attenuator), or let the automatic attenuation selector do the job.

There are many boards inside, but all nicely numbered and with instructions in the manual.

The HI and LO level detection is done on the A3B2 assy.

According the the schematic, U2, a MC1458 generic dual opamp is switching the LEDs and providing signals to drive the automatic attenuation selector.

A quick check revealed that U2 is defective, so I replaced it quickly, and this already solved the issue and brought back the display.

Another trouble related to unstable lock of the 2.3 GHZ auxiliary LO that is used for the 0.01-2 GHz range (which uses a two-stage down mixing).

Fortunately, I had a spare 2.3 GHz from my parts unit (which I bought years ago – a partial unit – while I was living in the US). That part was missing one of its covers, and had also some issues earlier, but I had fixed it a while back just for curiosity. Now I can fix the unstable 2.3 GHz removed from the unit during next winter. It has a 2.3 GHz VCO, a 100 MHz local oscillator and a PLL inside.

After calibrating all the oscillator frequencies, which went without trouble, I noticed that the top 120 dB attenuator was 0.04 dB off, well, not a big deviation, but I would rather have the unit working perfectly. So I removed the attenuator for further study.

It is build with really high quality relais, more than USD 50 (each!!), and some precision resistors.

Nothing could be found wrong with the unit by visual inspection.

Also I used the VNA to check the attenuator, and all seems well working.

All the 3 segments, virtually equal at 10 dB each.

Finally, I put everything back together, a little clueless, but, now, for some reason, all is working and stable. Maybe it was some lose connector, or other strange effect that is now gone. All attenuators calibrated perfectly, using by HP 3335A level generator (which has a top-accuracy attenuator).

Finally the 1295, working just perfectly fine. Maybe better than ever before.

Interestingly, as with all of these Micro-tel devices, the side and top/bottom panels were painted with various kinds of special military paint – some with a rubberized paint that will dissolve into some gluey substance over time, some with a type of “abrasive” paint, other already re-painted in forest green.

The paint has very large and hard grit, almost like sandpaper. But I will leave it untouched, it seems the original looks for this serial number range (the 1295 seems to have been in production for 10+ years).

Now, a little gallery of all my Micro-tel 1295 receivers: the first two, part of my frequency-locked attenuator calibrator (can measure reflection and transmission at the same time).

One as part of an E-band (60-90 GHz down-converter).

Any now, already two spare units in perfect calibration.

Still, in the basement, a box of spares… likely I won’t run short of receivers soon. Maybe even buy another one should it come around.