actually, not me, since i work for a warranty service center, but i saw the t-shirt and had to post a picture of it. it says "I void warranties" and has a picture of many common screwdriver bits used in consumer electronics. if it's broke and it's still under warranty, get it fixed for free, don't open it to poke around. if it's out of warranty, and you don't have a service plan you paid for, go ahead, poke around all you like, it's already broken and you will a) find something simple like a bad solder connection, b) figure out what component has failed, c) take it to get fixed COD (take my word for it, the repair will cost less if everything is back where it belongs), or d) give up on it and toss it and buy a new one.

there may be no such thing as a free lunch, but a free repair on a warrantied item (or maybe the manufacturer can't figure it out and gives you a new one anyway) is a pretty good deal if you can resist the urge to see what made the thing tick before...

i see (and answer) a lot of posts both here and elsewhere about 1kW inverters. my immediate answer is usually something along the lines of "there's no such thing as a free lunch". first of all do the math. 1000W/12V=83A. assuming about 15% in losses, that's pretty close to 100A. not only are we talking "heavy iron" here for a transformer, we're talking heavy copper too, since the wire used in the primary circuit needs to have negligible copper losses at 100A. you also need about 20 MOSFETs per side (of a split winding on the transformer) assuming 10A devices, and a safety factor of 2:1. that also makes for a very large heat sink. so basically we're looking for a "welding" transformer with a 12Vct @100A winding, 00ga wire (or at the very very least 2ga kept very very short) 40 MOSFETs, and a very big heat sink.

like i said above, there are 1000W inverters that can be had for free, but it takes a bit of looking to find one that works from 12V....

Screendump of the schematic done in Splan5


The PCB artwork in Jpg format

i'm compiling a counterfeit transistor identification guide. i've seen a lot of these in the last few years, and the counterfeiters are learning from their mistakes. these transistors are usually knock-offs of popular audio output transistors (such as the 2SA1943 and 2SC5200) or TV horizontal output transistors, or any other semiconductors that are normally in the medium-to-high price range ($5.00 US and up).

generally these devices are cheap devices bought in bulk, then have their original part number removed, and have it replaced by a part number consistent with a higher current/voltage/wattage device. for instance an audio output transistor rated at 200W, 300V, and 15A is counterfeited by taking a similarly packaged transistor (MT100 case style) that is only a 150W, 200V, and 10A device. the original part number is shaved, sanded, wire-wheeled or chemically treated to remove the original ink, or in some cases painted black to cover up the original number. the new number...

i started this blog because i have a few projects i'm working on and wanted to bounce some ideas around.......

when i originally set this blog up, i couldn't find a link for posting blog entries, now i've found out how, so here goes......

1) working on a white paper about audio power amp output impedance and feedback.

2) working on a device that directly measures AC impedance the same way a DMM measures DC resistance, and does frequency sweeps and impedance graphs (and a whole lot more...). this device is a spin-off of the first project. this is the prototype and is a completely analog instrument.

3)working on a DSP based version of the impedance meter, using the DSP chip to act as the waveform generator, as well as compute the results of various tests.

a couple of projects using DSP for Software Defined Radio.

people who have read my posts will see that i use LTSpice for part of my prototyping process,...