This week I bought twenty surplus Nokia RRIC boards. When I bought them, it was very clear the warranty was void... I bought the board very cheap, primerely for salvaging the N-connectors for hamradio use. And there are some nice other components like several xtal oscillators and smd chips for practicing my smd soldering skills. I knew the condition of the boad when I bought them and for the price I couldn't complain. But I wondered what happened to the board before I bought them... Are they been run over by a truck?! Not only parts are missing/split in half, but parts of the pcb are crackked or even missing, including half of the connector!
On the image is a Siemens Logo! plc shown. This (brand new) one was wired to 230VAC. Since this is a 24VDC model, the result was a lot of smoke and a 16A blown fuse. Since my colleagues know ham-radio operators can use all kinds of broken equipment for components it was brought to me. Fixing was worth trying so the relics of the evaporated component were removed and the evaporated pcb trace was replaced by a piece of wire. After cleaning up the black stains, the plc was wired to a 24VDC power supply. And it's alive again! Resurrection after electrocution is not bad I guess...
On the image in the middle are two voltage regulators shown. The right one is as it should look like. The left one is exploded. It's very likely this happened by overvoltage and not by a production fault.
Anyone who repairs old equipment are probably familiar with bad capacitors (by aging). Mains noise from old tube amplifiers is one of the indications of bad capacitors. Sometimes bad caps can be found by visual inspection since they start to bulge. This week I found two caps in a (still working) device. That they went bad could be seen from one meter distance... The first one is leaking (a lot) of fluid and is very bad corroded. The other one is dried out. When it was shaken, there is clearly a rattling sound to be heard. The exact age of the caps isn't known. They are at least two decades permanent in use; at least 175.000 hours...
Today I received two waveguide attenuators which I bought earlier this week. (For the record; model J382A and P382A, both from HP.) The "small" is in good shape, the "big" one... not so good. Since it was not packaged well enough, during transport one flange is badly damaged. The compression mark on the box can clearly be seen on the image, along with the other half of the flange. Luckily the cartboard box is not damaged badly and therefore it can be used again. ;-) And the attenuator... well, probably the housing will be used for another ham-radio building project...
The other day I started a repair project of a recently bought Kenwood TS-830M ham radio transceiver. The previous owner said there was "some problem" with the transmit function. After a thorough visual inspection the radio was hooked up to a variac. The voltage was (without any trouble) raised to mains level and some receiver functions were tested. I had a hunch that something was wrong. Therefore I setup a camera to record the final amplifier stage. During testing I checked the tubes visually and there was nothing wrong to be seen. Until two minutes after the powering up of the radio. The left tube started red plating, which I didn't notice.
One minute later the left tube failed by a bad flashover. I haven't examined the tube yet, but it's very likely that there's a grid/cathode short inside the tube. Grid/cathode short circuit seems to appear sometimes in these 6146B vacuum tubes. This all happened in receive mode.
The bad thing is that the previous owner soldered a wire across the (blown) mains fuse. (...) You probably can imagine the resulting damage. Probably this isn't the first time a seller lied.
Today a colleague of the IT department asked if I could repair a broken (as in two pieces) USB stick. The USB stick was installed in the front of a PC which was on the floor. Someone hit the USB stick by accident and the pcb traces came off the pcb. Note; the same colleague always strongly advises not to place computers on the floor to prevent this types of accident. ;-)
Well, the repair... I like soldering, but SMT isn't my favorite. I like challenges and this seems a good one to test my skills. After cleaning the connector and scraping off the protective paint of the copper traces, the two pieces are placed onto a breadboard pcb using solder wire and double sided tape. Then four small wires are used to create the point to point connection. The thickness of the wire is 0,25mm/0,01" (AWG30). The soldering wire is four times thicker and the tip of the soldering iron is even six times bigger than the copper wire. That's not the ideal equipment, but surprisingly the "repair" went quite well and rather fast.
Luckily there was a stereo microscope which made the job quite easy. And the assembly works! The documents are saved and this USB stick is added to the hall of fame (or shame...)