I have an uncle that owns one of those huge traveling carnivals. I get a call one day and he tells me one of his rides is down and his normal repair guy is unavailable. Hes known that I have some computer repair skills and some electronics skills so he ships me the part hes needing fixed. I honestly don't even remember what it was other than some power regulator for a dc motor controller or something along those lines. It had something to do with controlling the ride motors. I receive it having no schematics or manufacturer information and proceed to take it apart. Boom right there staring at me is a burnt up massive resistor. It was nearly an inch long big one. Thankfully I am able to read part of the part number on the side and after a very long googling and research session I find the correct part. I live near by Mouser Electronics so I can pickup the part super quick since he needed it back right away to setup and test. I order using will-call and grab the part and was able to solder it back in using my really basic 12 or whatever watt weller red handle soldering iron I got from Lowes. I was so excited I could help him out and I think he sent a few bucks my way once it was all repaired. He has since moved the carnival to China and Taiwan since the crowds here don't care much for carnivals anymore even before Covid.

Let me first say I am only a hobbyist self taught and by no means any sort of technician.

My brother owns a very popular manufacturers telescope and suddenly it stopped working and failed to power on.

As it was out of warranty he asked me to take a look at it due to the cost of the repair was more than the cost of a replacement.

When I received it from him I soon discovered there was a direct short between ground and the +12v rail in the computerised mount..

I contacted the manufacturer who wouldnt offer any real assistance, and only kept telling me i need to purchase an upgraded mainboard for the mount.

I dont give up quite so easy

I worked my way through the board and soon discovered that there was no real supply protection circuitry within the mount and having tested all of the surface mount caps and regulator which would usually give this type of fault i turned to what was left, just the main IC's.

i desoldered the 80pin kinetis  MK20DX256VLK10 and replaced it with a blank chip and bingo, the mount powered up.

obviously it wouldnt work as there was no software on it.

I then contacted the manufacturer of the mount again and explained the issue was the main processor and discussed with them the lack of protection circuitry, they assured me the updated main board has better protection and I would need to still purchase a new board.

I asked them if it was possible to get the firmware for the processor as I could not read it from the damaged chip so I could at least get this board back up and running, they wouldnt help me with it

As my father always said tho, theres always more than 1 way of skinning a cat

I know the manufacturer releases bugfix's for their hardware, so I turned my attention to their latest bugfix update package..

It is released as a java package( im not a computer programmer either by the way)

but I do know winzip can be used to unpack java,

I ended up with a full directory of about 100 java files which I started going through to give me some ideas of what and where to look at.

at the same time I wanted to understand how the package updated the kinetis chip,

from the update instructions, i knew the software used a serial connection to the hand controller

I made up a serial lead and instead of connecting it to the hand controller i connected it to a raspberry pi,

i wrote a small python script to capture any binary data from the pc that i was running the update software on,

it didnt capture very much so i started echong it to the screen using a bin2hex library.

after a while of looking at it, i noticed there was something common within it, basically a set of 3 bytes,

i inserted a line break at every occurance of these bytes and soon realised they were basically being used as start and stops.

I looked for these bytes in the java code and then learned that these were indeed the start and stop bytes, the next pair of bytes was an instruction byte followed by the data and then length and then a checksum.

knowing all this, i then connected the raspberry on a seperate serial port to the hand controller, and ran the update again.

i now could see data coming back from the hand controller as well, the hand controller was looking for any attached hardware.

i knew without any software on the mount it would not see the mount. so i started digging further into the java software.

I found when it searched for the software on particular responses it would read in some binary files, i managed to figure which binary files was associated with each type of hardware and most importantly which ones was used for the mount i was working on.

each of the binary files had their own file headers and data sections which i was able after many hours to figure out.

there was in total 7 binary files required for the mount and each file was lightly encrypted with the exception of one.

I read up on the kinetis bootup and found it could be programmed in such a way that the bootloader could be at the top or bottom of memory,

the mount had a 2nd large flash chip in it which was unharmed, and knowing the way the kinetis chip maps memory and uses a flash chip i knew the bootloader would have to start at address 0x0h and the most it could use was 400 bytes.

i dug into the java many times rerunning and recapturing responses from the hand controller and started inserting my own responses from what i was learning.

after a few days i finally was able to capture the bootloader being sent from the suspected binary file to the hand controller which should pass it to the motor controller.

obviously the hand controller couldnt pass it as it was my responses on the raspberry  that triggered it being sent from the upgrade package it wasnt the hand controllers.

but i had now got the bootloader stored in its binary decrypted format on the raspberry

now the easy bit

burn the bootloader to the kinetis chip,

i found the pads for what should be a jtag interface on the board and tried to burn the bootloader via that, it was quickly apparent that it wasnt working. after some tracing i discovered that it wasnt completely connected and had to solder a thin wire directly to the unconnected pin on the kinetis chip.

as soon as i did this i was able to program the bootloader in.

woohoo, getting somewhere ))

fingers crossed now,

i ran the upgrade package again, still capturing everything on the raspberry.

bingo!!!!!

i could now see the hand controller replying to the upgrade software that there is a mount attached.

i selected the mount and software package within the upgrade application and i was able to fully update the mount with the latest software )))

My brother is a happy bunny now, his mount completely working again for the price of a £10 chip and some time and patience.

Im happy as i was able to fix it for him and learned so much in the process )

I have since connected the raspberry between the hand controller and the mount and captured all the commands on that for its movement and speed controls etc,

The intention is to write a small program that will interface between an open source PC application and the mount so he can use it connected to the PC as a computer controlled mount for looking at distant galaxies and nebulas.

About 7 years ago I got a panicked phone call from my wife who told me the tall freezer in the kitchen was making a beeping noise and it was quickly defrosting inside.

I had to come home from work to try and save the hundreds of pounds of food going bad, when I got back home I found that there was no life in the freezer other than the beeping noise and a warning LED on the top panel inside the front door.

I disassembled the controller on the back of the freezer, it's a large PCB originally intended for washing machines etc and repurposed for use on other appliances, the control panel at the top of the freezer communicates with it via I2C. Unfortunately the big PCB at the bottom was dead, only the power supply was working but the 'receiver' part (just another micro) was dead. Scoping the crystal showed there was clock activity but no response on the inputs or outputs.

As a temporary measure I connected the compressor and circulation fan directly to the mains and plugged the freezer into a 24H timer, so it ran 45 minutes off, 15 minutes on. This worked for a few days but wasn't apropriate for long term as it wasn't temperature controlled and also the freezer is a frost free unit so the condenser unit fills up with ice eventually and an electric heater has to be turned on in order to melt the ice and restore efficient operation.

My eventual solution was what can be seen in the pictures, stuck to the side of the freezer cabinet. It was only meant to be temporary but here we are 7 years later!

The solution consists of cheap 12v relay modules which interface to the compressor, Fan and heater. powered by a nice reliable 12V linear mains transformer, and controlled by a PIC18F2520. It takes the inputs from the existing 10K NTC thermistors in side the cabinet and a potentiometer. It has an 4 x 20 LCD display for status information and also has a bluetooth module for communication, which I can use custom AT+ commands to check the status, log data and command the unit to run defrost or override the temperature contol input etc etc.

I am mostly a hobbyist that tinkers at home. I've revived at least a half dozen toys for my boys already usually by soldering back on cords pulled out of remotes or replacing batteries that weren't necessarily meant to be replaced.

In my day job I work with research instrumentation. This is my baby: It is Mossbauer spectrometer used for measuring the resonant nuclear absorption of the 57Fe atom. We use it to understand iron geochemistry. And every time I have to take it apart for service, I need to desolder several connections.

Anonymous-762148  Better lucky than good - sometimes.

I decided to build my own running race timing system after not being able to find anything affordable to do the job. In test this system worked perfectly, however whenever the case was closed and then moved/touched it would trigger an unknown series of events leading to it falling over. Several months of head scratching and code changes on the microcontroller I realised the gap between the circuit board on the lid and the circuit board on the bottom was only just definable as a gap. Just. Hot glue and plastic sheet and it was fixed.

Hello everyone, a hobbyist here. My best electronics repair was troubleshooting a laptop motherboard and replacing 2x mosfet driver ics(usb power and cpu power) that were shorted out. The laptop booted fine first try.

At work i do bga ic replacements on specialised tools and it is always a happy day to learn that my board is working after replacement.

Best microsoldering result was replacing a cpu socket pin.

A great repair job. I tend to agree with you that the joint was more likely sparsely soldered in the first place rather than dripped the solder off due to a fault. I'd expect if the joint became hot enough to melt the solder you'd have also see flux or lacquer damage to the PCB.

Long ago I had a boiler that failed and spent several days trying to fix it (the non-gas/burner components only) - you may well recall your own memories where everyone is feeling dirtier and asking to shower at friends houses. For me after several days of intermittent operation I realised the PCB flexed slightly as I was probing it with the multimeter and occasionally this caused it to flash up....PCB out, into shed, reworked all the joints (a nice simple single sided PCB) and back in....water on....washed dishes/baths etc...everyone happy again. My point being boilers do develop dry joints.

Hi John,

Firstly, welcome to Element14 community . What a great setup you've built and designed there and thanks for sharing. Have you spotted the Project14 area on Element14 yet? You might like that - there is a monthly theme and people make stuff for various prizes or shopping carts. Animatronic gadgets seem to go down well IMO and there's always a large amount of online help/suggestions if you ever get stuck in the techy side.

I recall stopping at the Steampunk area on a London Comicon in the past and being amazed with the detailed gadgets and designs they produced. One in particular consisted of lasercut stainless sections that rose up out of a sphere to make a intricate flower...how they even contemplated such a design was beyond me.

The challenge was converting an RV refrigerator from an ammonia vapor absorption cooling system to a freon compressor cooling system.  This required that the freon compressor be hooked to the terminals that used to provide power to the vapor absorption system boiler. The instructions that came from the supplier of the conversion system state that the warning beeper must be disabled and the users must simply ignore the flashing error codes on the fridge front panel that indicates the heater elements have failed. (It will give this error continuously because the freon compressor draws only 1/10th the power that the heater elements did.) I deemed this ham-handed approach (disabling the warning electronics) ridiculous! What was appropriately required was to re-engineer the fridge control electronics so that it accepts the much smaller power (load current) of the compressor as a valid operating level.

My goal, therefore, was to raise the sensitivity of the AC Heater current sensing circuitry so that it would accept the 125W load of the small freon compressor in place of the 1500W boiler heater, and not have the control logic give an error/fault indication of Open Load/Sensor ("Sr OP" was the fault displayed by my particular board).

Having no schematic for the control electronics, and having been told by the manufacturer of the control board that the schematics and circuitry are proprietary and cannot be shared, I began the task of reverse engineering the control electronics. I soon determined, by tracing out the pathways on the printed circuit board, that the heater load power was sensed via a 500:1 ratio current transformer.

"Aha!", I thought, "All I have to do is increase the value of the 'burden resistor' on the output of the current transformer to achieve the desired increase in sensitivity. (Since the output of current transformers behave essentially like constant-current sources, their secondaries are typically loaded by a burden resistor to achieve the desired volts-per-amp output (i.e. turns-ratio x burden resistance = volts per amp). However, and much to my surprise, I discovered that the burden resistor footprint on the circuit board was not populated on the board (no part was soldered thereon)! Without a burden resistance the secondary of a current transformer will try to rise (trying to push current through an infinite impedance) until it reaches the saturation voltage of the coil! (Not the usual practice, to be sure.) I did note that current transformer's secondary was provided some loading through a diode and capacitor feeding a voltage divider (comprising, I believe, a passive integrator/filter circuit to translate the signal to an appropriate trigger level).

Not having the option of increasing the burden resistance (since a missing resistor is the same as a resistor with infinite resistance) to achieve the increased Volt-per-amp sensitivity, I was still left with the option of altering the turns ratio on current transformer to achieve the desired sensitivity. This necessitated unsoldering the transformer from the board, taking it apart and replacing its one-turn primary with six turns of 18AWG magnet wire. This lowered the turns ratio to ~83 and increased the sensitivity, allowing me to populate the burden resistor footprint with a 5.6K burden resistor to achieve a sensitivity of ~2.5V across the burden resistor per amp of primary current.

The control board now functions properly with the compressor as its load, and still has all the load-sensing functionality and other features intact!