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June 05 2017

Welder repair

An ancient proverb says that power tool failures occur in threes. During the same week that the lathe motor burned out and the compressor wire meltdown has turned it into a scary noise machine, we also had a mysterious malfunction in one of our welders. It didn’t release any smoke, didn’t make weird noises. It just didn’t weld. 0 volts across the output.

Inside of the welder (top view) before the repair attempt. Note that a large number of similar – but not identical – top boards can be found on Aliexpress.

This machine, a small 180A TIG/MMA inverter welder, has recently been repaired. It was not used heavily, as TOG has only so much use for welding. In fact, it was only used by a couple members to practise their welding skills.

On one hand, this machine was 5 year old, has been used extensively in the past and could have been written off as death of old age. The cost of a commercial repair would probably exceed the value of the welder. On the other hand – why not try to repair it ourselves before scrapping it?

So, first pass – take it apart and look for obvious damage, like blown up MOSFETs or rectifier diodes. Nope, nothing there. All power resistors look intact, too. All cables securely plugged in. No charred FR4. Nothing clearly damaged or even suspiciously-looking.

What next? Seems hopeless. First, we don’t know how an inverter welder works exactly. Second, we don’t want any deaths, either from electrocution or any other reasons.

The safety problem was somewhat addressed by setting up all the probing while device was unpowered – both in terms of mains and its storage capacitors. The device was only powered for a few seconds to read the measurements off the screen, without touching anything. All measurement instruments were battery-operated, to avoid unintended coupling through protective earth in mains-operated instruments. This approach doesn’t really avoid all dangers, but at least addresses the well-known risks.

The lack of knowledge issue is solved by a rabid and desperate search for any possible schematics and repair hints, from Chinese search engines to Polish electronics repair forums and, of course, various chip manufacturer datasheets. Turns out that many of the MMA and TIG machines from the last decade are variants of the same 3-board design (+daughterboards). We haven’t found the schematic for the machine in question but we didn’t really need it – a PDF schematic of a 160A MMA welder found using Chinese image search was very helpful in identifying major blocks and their connections. A TIG machine obviously contains more logic to handle the TIG functionality (gas valve, pulsing, HF/HV arc start etc.) but those were ruled out as a likely root cause.

All of those welders have a common set of functional units. A primary-side rectifier on a lower board rectifies the 230V mains voltage and provides slow-start functionality to prevent power surges. A power MOSFET module on the top board does all the switching work. Then there’s a set of transformers and secondary rectifier diodes on the middle board that provides output DC voltage for welding, with help of some power chokes to filter out the switching AC component. The whole switching process is controlled by a drive module on a vertical daughterboard, which in turn feeds a H-bridge of small MOSFETs that feeds a transformer that provides gate voltages with correct polarity for all the power transistors. Sounds complicated, but at least everything is nicely divided into modules with a well-defined purpose each. The drive circuit is powered by an auxiliary 24V power supply that turned out to be one of the known weak spot in these units, according to some forum posts.

So, the investigation first looked at the output voltage from the power MOSFETs. There was none. Input voltage for that block – present. So, it will likely be something between the primary rectifier and the output from the MOSFET module. Broken MOSFETs? Nope, they measure fine. Is there a gate signal? Nope. Not on the power MOSFETs themselves, and not even in the H-bridge that is driving the gate-drive transformer. So, perhaps it’s the drive module. After a few hours of connecting alligator clips to various points (heavily coated in non-conducting lacquer, by the way) it was apparent that the SG3525A that was supposed to generate signal that (eventually) drives the power MOSFETs was shut down by one of three protection circuits. There are several: overheating protection (based on temperature switch) – certainly not an issue here. Overcurrent protection – also not to blame here. The one that turned out to be responsible was the undervoltage protection for the 24V supply. Why is too low a voltage a problem? because keeping switching MOSFETs in active region instead of saturation makes them overheat and fail very quickly – and insufficient gate drive prevents saturation. And, bingo – the aux supply voltage was definitely below the usual 24V. The actual value depended on which modules have been left connected – with TIG timing board connected it dropped to almost 12V! Without it was still 19V or so – so, it was definitely a wimpy power supply issue, not, say, a short on the TIG timing board. Trying the welder with 24V supplied from outside (via isolated lab supply) confirmed no other faults – the machine seemed fully working with that setup.

The 24V supply is a flyback converter, based – in this case on a UC3843 PWM chip. In other welders, it may be a bunch of discrete components instead. The converter is using a 200:33:33:16 transformer. One secondary winding used to provide the output voltage, which is then rectified and compared to 24V threshold, with feedback given via an optoisolator. Another, smaller secondary is used to power the PWM chip itself, with help of a standard rectifier diode and a filtering capacitor – although the initial voltage is provided with a high-value high-wattage resistor directly from 310V. There’s also a current sense on the primary that limits the current going through it to 1V/2.2ohm =~ 0.45A.  The initial suspicion was that the transformer had burned windings which didn’t provide enough current. However, this turned out to be incorrect. The transformer looked perfectly, and replacing it “just in case” would involve waiting and risking damaging the board, already damaged a bit by a careless replacement of a perfectly well-behaved filtering capacitor.

A careful observation with an oscilloscope revealed that the voltage on the Vcc of the UC3843 was drooping as the chip was outputting PWM pulses, getting below the undervoltage lockout of the UC3843, then recovering slowly after some time. So, that small secondary winding wasn’t providing enough power through the diode. But why? Bad transformer? The diode itself tested perfect.

What ended up being the root cause was a broken track on the PCB, between the diode and the rest of the Vcc-related circuitry. So, the PWM chip was only powered through a high-value resistor and running out of power quickly as it started generating the PWM pulses, without getting any extra power via the aux secondary. This caused a weird “a bunch of pulses, then silence, then the cycle repeats” behaviour seen on the oscilloscope, correlated with variations in chip’s Vcc. A piece of wire to mimic the function of the broken trace fixed the 24V output and allowed the rest of the machine to work correctly.

NERP Tonite: MOSFETs with Ste!

Mosfets – They can be “on” — They can be “off” — They can even be in between! Tonight at NERP, entrepreneur, engineer, and really good teacher Ste Kulov will guide us into the world of mosfets. Metal Oxide Semiconductor Field Effect Transistors if you want to impress your friends.

N-Channel MOSFET [wikipedia]

Since mosfets are a wide and deep subject, I asked Ste where he wanted to focus his talk. With great economy of words, he said it better than I could.

“Most of the generic stuff, fairly quickly.  A few simple examples I was probably going to cover are: making a logic inverter, a logic controlled load-switch, and reverse battery protection. Simulating in LTspice [circuit CAD], since I can draw that stuff in two seconds and put it on the screen.  If you want to do a power MOSFET application, I would need to see the datasheet for it.  Also keep in mind that high current stuff is no good for breadboards. If you need a list:  4 vs 3 terminal, body diode, Rds(on), gate drive, switching speed, N-channel, P-channel, CMOS digital logic, CMOS analog switches.”

NERP is not exclusively Raspberry Pi, the small computer and embedded systems interest group at Pumping Station:One in Chicago. NERP meets every other Monday at 7pm at Pumping Station:One, 3519 N. Elston Ave. in Chicago. Find NERP and Pumping Station:One at­

Tags: electronics, embedded, NERP, Open Source, raspberry pi, hackerspace, Beagle Bone, Pumping Station One

June 04 2017

Spindles of Wood

“Spindles of Wood” is not the name of the latest album from some obscure Icelandic emo band! Instead they are actually the front wheel spindles for our No-weld PPPRS vehicle. (You probably remember the frame from last time.)

While most teams in the Power Racing Series just buy pre-made spindles and weld them in place, our “No-weld” spindles were built using wood, glue some staples/screws, and use some 5/8″ bolts to attach to the car, and for the wheels to attach to.

We’ve still got to get the whole steering thing worked out, but we’re on our way! (Things are moving a bit slower than we had hoped, so we might debut this thing at Detroit in July instead of Kansas City in June, but we’ll see how it goes.)

June 02 2017

Sommerlukning 2017

Da er det sommer igjen og biblioteket har begrensede åpningstider.

Vi holder da til på digital verksted mellom 16-18.

June 01 2017

3 Scoops of Signage

Julie and Carl of Scoops Ice Cream & Candies of Kenosha, approached new Makerspace member, Brandon Minga, with their project. They were given recommendations from other projects he’s done in the are including Mike’s Chicken & Donuts and the Modern Apothecary. Scoops was looking to enhance and draw more attention to their new location with a large exterior sign. Going through the concept and design process Minga quickly decided that the sign design was also going to become their new logo. Once the final design was rendered he quickly learned how to CNC a template to hand plasma trace the design out of sheet metal. The middle of the sign was also hand cut, roll bent and broke to match the bubbly ice cream cone shape. With a little help from friends a the Makerspace, he ground down welds and drilled 44 holes for the light bulbs. After all the holes were drilled Minga fit the sign with sockets, wired up the sockets and tested the electrical. Working with Prodigy Sign in Kenosha he also coordinated the hanging of the sign.

Any project starts with a sketch.

Nothing wrong with learning a little g-code.

A post shared by Mingadigm (@brandonminga) on May 2, 2017 at 12:47pm PDT

Took that g-code and used the handmade CNC router to cut out a template (note to self, don’t use OSB for plasma templates).

Traced template with hand plasma cutter.

Hand cut, roll bent, metal break and tack welded the bottom shell.

Hand cut and used the break to bend my own c-channel for the stabilizing guts of the sign.

<!--[if lt IE 9]><script>document.createElement('video');</script><![endif]-->

A little help from my friends!

A post shared by Mingadigm (@brandonminga) on Mar 31, 2017 at 3:33pm PDT

A little custom install and wiring….and we have lights!

Can’t forget the paint! Primed inside and out, the sign got coated with some retro color.

Installation day was very windy, they called two crews in to stabilize the sign as they anchored it to the building.

This is a by Brandon Minga

This project was done at the Milwaukee Makerspace,  thank you, gang!

May 31 2017

06-10-2017 An update on Cybersecurity Regulations & Standards

“As infosec professionals, we have to keep up on the latest threats and issues emerging in cybersecurity.  Certainly the recent WannaCry incident is a perfect example of this. But in addition to that, we also need to keep abreast of updates and changes in regulations, standards and the like that can also affect us and […]

May 30 2017

Making stuff for scientific conferences

Last year I was making little things for a conference my work organized in Chicago.

You’ll find more info on my blog posts. But as a teaser, it involved laser-cutting, glue, Inkscape and a lot of mistakes (but I didn’t took pictures of those, too bad).


A person touching a device

Slide Ruler

Circular slide-ruler in acrylic on plywood board.

Demonstration für echte Netzneutralität: Mehr Datenvolumen für Alle!

Am 31. Mai 2017 ab 9:00 vor der Lanxess Arena in Köln. Kommenden Mittwoch findet die Hauptversammlung der Aktionäre der Deutschen Telekom AG statt. Im Vorfeld sorgte die Telekom mit "StreamOn", dem neuesten Angriff auf das freie, offene Internet für große Aufregung. Anstatt den eigenen Kunden mehr Datenvolumen zur Verfügung zu stellen, versucht die Telekom sich als Gate-Keeper für Online-Inhalte zu etablieren.

May 29 2017

We’re open for Craft Night

May 28 2017

Quick Layout: Four Hole Bolt Circle

You don’t always need a CNC machine or thousands of pounds worth of equipment to get the job done. Here, we’ll be laying out a 4 hole bolt circle suitable for mounting something like a stepper motor or bearing flange using just a ruler, compass and centre punch.

Mark out your material, and centre punch the middle. This will be the punch mark for the central spindle of our motor. Scribe a straight line through the centre in the orientation that you want for the first two of your holes. This is your base line.

Set your compass dividers to the radius of your required bolt hole and scribe your first circle. Centre punch the two intersections of your scribed line and the circle.

Set the dividers to around about the diameter of the bolt pattern, and then scribe a short arc either side of the baseline using each of the perimeter punch marks as a pivot.

Now that you have intersecting arcs on either side of the base line you can carefully scribe a line between them, ensuring that you head straight through the centre. Punch on the intersection of this new perpendicular line and the circle.

If you have a lot of further layout to do you can touch up an construction lines with the layout marker to keep the work space easy to understand. As with all these sort of things the amount of care you take when placing your punch marks, and setting the compass width, directly influences the quality of the end result. Use a magnifier if you need to!

Transcyberian Crypto-Party 16.6.2017 18:00h

We are very proud to bring the Transcyberian parties from Paris to Berlin!

Transcyberian is a series of club, noise, queer and nerd friendly events featuring futuristic, crypto and activism workshops and experimental electronic performance and DJs. Transcyberian is a hybrid concept inspired by CryptoParty. Our events are LGBTQI+-friendly. As we want everyone to be welcome, there is no entrance fee at our events – however if you can afford a donation, it would be much appreciated.

For our first event we decided to donate all the money we will collect to the Chelsea Manning legal fund operated by the Courage Foundation.





6pm – 11pm : Workshops
Adam Harvey – Facial recognition
Leif Ryge – The pocket litter exchange
CryptoParty Berlin – CryptoBar
more tba
11pm : Live performance
Widescope – Experimental Silence Performance
Midnight – open end: Party
Various Vegetables DJs:
Eutechnik [A/V]
Vertical 67

Late May and Early June at Tog

Hi everyone, we’ve another two weeks of Tog’s regularly scheduled events for you to enjoy.

Monday May 29 – Coding Group Night from 19:00
Tuesday May 30 – Lockpicking Group Night from 19:30
Wednesday May 31 – Crafts Night from 19:00
Monday June 5 – Electronics/Microcontroller night is on from 19:00

Hope to see you there!

Because 3D Printing…

3D Lock

Sometimes you see amusing things at the space. Take for instance, this lock on the bathroom stall. The black piece is actually 3D printed. Yes, someone took the time to measure, and model, and 3D print a rectangular bar to fix the bathroom stall door lock.

Never mind that a piece of wood, or plastic, or metal could have probably done the job in much less time, sometimes you just need to 3D print a replacement part for a bathroom stall door and you bust out the 3D printer and in a matter of hours you’ve got the part you need!

May 23 2017

OpenChaos am Freitag, 02. Juni: Interim

Das OpenChaos am 02. Juni wird sich mit Interim, einem minimalistischen Betriebsystem mit Anleihen bei sowohl Lisp Machinen als auch Plan 9, beschäftigen.

May 22 2017

Air compressor fixed

Air compressor in workshop died few week ago and finally getting around to taking it apart to see what issue is. Seamed like motor might have ceased however it was quick fix. 

May 21 2017

TOG Calibration

If you work in industry or business, you probably have your electronic test gear and multimeters calibrated regularly. If you’re an amateur you probably don’t. We don’t have a fancy calibrator at TOG which can cost 1000’s and need regular calibration in itself. We do however have a 2 Euro voltage reference based on an Analog Devices AD548 voltage reference. Checking some of the multimeters that we have around, and the results are surprising.

The reference outputs 2.5, 5. 7.5 and 10V. Now this is a bit of a crude test, because this little reference is not calibrated or traceable to any standard. If you assume however that the voltages it gives are “exact”, a 20 year old Fluke multimeter is reading almost perfectly . Some other multimeters that we checked are a bit off, but still not too bad. We’re going to check some of the ultra cheap meters that we have too.

Fluke 77: 2.499, 5.00, 7.50, 10.00
Standard ST-3343 Clamp Meter: 2.495, 5.01, 7.51, 10.02
Velleman DVM890: 2.47, 4.96, 7.44, 9.92

May 17 2017

TOG May Open Social

Our May Open Social evening takes place on Saturday 20th May from 7PM.

If you’ve never been to our Social, you’ll find it a great alternative Saturday evening in town. Come in and look around. If you’ve never been in before, we’ll give you the grand tour of the space. Talk to members and visitors about projects or things you’d like to do. Ask us about the next phase of our plans for the space and our big cleanup. If you like what you see, ask about joining as a full member. If you see lots of excited people playing with small robot cars, don’t worry. We were running our Electronic build-It workshop earlier in the afternoon!

Hopefully there’ll be, caint, ceol agus craic as usual. The space stays open until the last member is left……usually the small hours of Sunday morning. The evening is free to attend for members and visitors alike. No need to book…. just turn up. You can drop in for 10 minutes, or stay the whole night. We have parking available. Bring beer, food, gadgets! Our doors are open from 7PM. Hope to see you there.


Bronze Casting!!!!!!

As you may have noticed, the Small Metals area has moved to where hot metals used to live. The process has been gradual but successful. We conducted an experiment over the weekend involving plaster investment and molten bronze. There were many variables in this process including new-to-the-space machinery: the kiln, the electric melting furnace, and the vacuum investment table. As well as different materials used, possibly expired flux, a new kind of plaster, and a type of bronze that had been melted a number of times before. All in all it was a great success. Here is a brief overview along with some photos to enjoy.

Seen here is the kiln at a glowing red temperature of 1,500 degrees. The molten bronze getting ready for the pour. Also seen in this picture is the vacuum table for the cast to help pull the metal through the investment.

The Termolyne mini melt electric melting furnace! Bronze has a melting point of 1,742 degrees 

The pour!


Fresh out of the pickle!

-Ella Gentz

May 16 2017

Visitor projects: the most excellent blanket
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