This site is dedicated to providing useful information on a particular problem that some are having with the Icom IC-2100H. This fix deals with the APC (Automatic Power Control) overheating due to either a) a mismatched antenna, causing high VSWR, or more likely b) faulty choice of parts by Icom, resulting in a transistor (Q19) that cannot handle the high temperatures found inside the 2100H. Symptoms include... a) no/low power output - keying up the radio produces only a few milliwatts output, from the exciter circuit. b) full/excessive power output - resulting from a short across the transistor. This prevents the operator from being able to switch power levels (Hi, Med, Low). Icom's service bulletin indicates their service technicians are to treat this as a "mismatch" of antenna impedance, thus placing the fault with the user, however, the fact that they now ship IC-2100H's with the modification already performed, combined with the fact that they provide this material, as well as a "fix kit" indicates to me they are well-aware of this engineering flaw. They will charge you about $100 to fix this and deny any wrongdoing whatsoever. Coincidentally, I have reports that they accused some individuals of opening the radio themselves (thus, voiding the warranty, and elevating Icom above any suspicion, also providing a vehicle by which to charge customers for the repair), on radios that were new, and had never been opened at all. I like Icom radios, but this sticking point provides a bit of "heartburn" to me. Here's most of the material on the subject that I have collected. There are several diagrams, pictures, and schematics included. <<>> This is a fairly simple fix, and inexpensive too, provided you are confident with your soldering/fabrication skills. In a nutshell, there is an Automatic Power Control transistor, Q19 (replacement: SK9458, about $3.15), which overheats and melts the solder underneath it, causing the transistor to go bad. The fix is basically to replace the transistor, adding a heatsink (in the form of a small piece of metal) and being careful to not let the heatsink touch the case of the radio when it is powered up. Here's the text of some of the emails... Tim, To answer your question about the heat sink, yes, it is a small piece of copper. However, as Icom has designed it, it does not allow contact with the transistor (except where it solders to it). This is apparently important says Icom. Also, what ever you do don't remove the little rubber piece (on the chassis) that is directly under the transistor! I, thinking I was helping matters, removed this rubber piece to try to allow an air space completely around the heat sink. Well, what I didn't account for was that because the tolerances are so close simple vibration of the radio allowed the heat sink to touch the chassis resulting in another bad transistor (the heat sink solders to the collector of the transistor). Although, I thought enough to have ordered two sets of transistors & heat sink mods to allow me to replace them once again but this time putting back the little rubber piece. That was the last time I have had to mess with it. It has been working 100% ever since - about 2 years ago. I can't seem to find the paper work from Icom when I purchased the parts but if I remember correctly the transistor was only a few bucks (if that) and the heat sink mod was somewhere around 9 cents each. I think I paid as much for shipping as the parts - although they did mail via USPS. When I repaired my unit I think the replacement transistor was the same part number. It could be that now, two years later, they might be replacing it with a different part number. More reason to contact them to be for sure. Regards, Richard kq4kx Tim Dixon wrote: Richard, I'm extremely greatful to you for the valuable information you provided. Do you happen to remember if the transistor Icom sent as a replacement was also a "B934", or did they change to another transistor? I've cross referenced this piece to an SK9458, and have found one online for $3.15. I think the heat sink mod will be easy enough (I too am a Comm/Nav technician for the Air Force, servicing radios and radar systems). Is it simply a small section of flat copper sheet? The picture you provided was super helpful in locating the culprit! SK lists this transistor as a PNP Power Switch. That would jive with this being an APC transistor. I don't have a cross referenced diagram of this transistor, so I'm not sure about this, but this is what I get when checking it with a DMM diode checker: back (positive) --> left leg (negative) = .600 back (positive) --> right leg (neg) = infinity back (negative) = infinite to both legs left leg (positive) --> right leg (neg) = infinite reverse = .600 Many thanks! Tim Dixon, KG4MIQ Montgomery, AL I found a couple of SK9458's locally at an electronics shop, and purchased two, just to have an extra. I fabricated a piece of heatsink from some suitable material cannibalized from an old computer monitor. I have not had any problems whatsoever since fixing the radio, but I also added a chassis fan, using zip-ties, just for added insurance against overheating. The chassis dissipates heat much better now, even without the fan turned on. Not nearly so hot as before. Care must be taken not to allow the heatsink to touch the chassis, since they are at different potentials. The chassis is at ground, while the heatsink will approximately 6 volts on it, thus necessitating the rubber pad which insulates the transistor from the chassis. When keying the radio, the exciter circuit is still functional, which explains why it is still transmitting a few milliwatts, and can be picked up by other radios nearby. I think the pictures and scanned images are fairly self-explanatory from here. Happy hunting! Hope you can fix your radio now! 73, Tim