From: sseeger@stellartec.com (Steven Seeger) To: "'webmaster@qrz.com'" Subject: ICOM T81A Mod Date: Wed, 23 Jun 1999 10:35:26 -0700 I'm not sure I'm sending this to the right person, but it'd be great to see it listed in the RADIO MODS section. I've noticed you don't have any mods for the T81A quad bander from ICOM. I just wanted to say that after reading the other mods for various radios I've figured out the receive mod for this one. It seems to be a touch trickier. The radio must be powered off in VFO mode so that when you turn it on, it isn't in the memory channels. Hold down SQL and the MULTI button (you must hold down the button as you would confirming choices in the radio, ie not in any one diretion but all of them) and then viola, there's all the receive. Just wanted to share it with everyone. :) -Steven KF6WJH Rob Neff (N7ORY) writes: Removing the battery pack and two screws at the bottom. Remove the antenna and ring-nut, also remove knob. Lift the circuit out carefully. Below LCD, right side of pcb, there will be 5 or 6 places for diodes. 1st and 5th diode installed from factory. To the right of small diodes, another set of larger diodes parallel to the row of smaller ones.. The layout looks like this.. [-] [ ] ( ) [ ] ( ) [ ] ( ) [-] They are labled (from top to bottom for the small diodes) d55,d54,d57,d66,d61.. The larger ones are labled (top to bottom) d53,d52,d51.. To open TX, remove the diode from the 5th spot down in the row of small diodes (d61), and also remove the first of the larger diodes (the one at the top, d53). This mod does not require resetting the cpu. New TX freq limits: 50.000 to 54.000 MHz 136.000 to 173.995 MHz 400.000 to 469.000 MHz 1.2 same To open TX farther, remove the first smaller diode, d55. This appears to TX on 220. It does open up 5 meters however. It will TX above 54 Mhz. The first mod does NOT open 5 meters. 50.000 to 75.000 MHz 136.000 to 229.000 MHz 400.000 to 599.995 MHz 1.2 same. From: "Rob Neff" To: Subject: IC-T81A MARS/CAP MOD Date: Wed, 18 Aug 1999 10:04:56 -0700 This is the complete mod. Please read completely. Open the radio by removing the battery pack and the two screws at the bottom, inside the back. Then remove the antenna and the ring-nut that holds that in place, also remove the knob. Lift the circuit out of the case carefully. Looking at the front of the unit, cover off of course, just below the LCD on the right side of the PCB there will be a series of 5 or 6 places for diodes. On my unit, only the first and 5th diode are installed from the factory. Just to the right of those diodes is another set of larger diodes, three of them, in a row parallel to the row of smaller ones.. The larger diodes have 3 legs. The layout looks like this.. [-] [ ] ( ) [ ] ( ) [ ] ( ) [-] They are labeled (from top to bottom for the small diodes) d55,d54,d57,d66,d61.. The larger ones are labeled (top to bottom) d53,d52,d51.. The 6 legged diode to the right of the larger ones does not get messed with! Its d58 BTW Ok, now for the meat. To open TX on the T81, remove the diode from the 5th spot down in the row of small diodes (d61), and also remove the first of the larger diodes (the one at the top, d53). This mod does not require resetting the CPU. New TX freq limits: 50.000 to 54.000 MHz TX 136.000 to 173.995 MHz TX FM 400.000 to 469.000 MHz TX 1240.000 to 1300.000 MHz TX To open up TX farther, remove the first smaller diode, d55. This appears to TX on 220. It also opens up 5 meters. It will TX above 54 MHz. The first mod does NOT open 5 meters. On my unit it will only go up to 63 MHz before it unlocks though. 50.000 to 76.995 MHz TX 136.000 to 229.000 MHz TX 400.000 to 599.995 MHz TX 1.2 GHz stays the same. Operate responsibly and never transmit out of band unless you are licensed and the radio is type accepted for that frequency. These diodes are VERY small and its very easy to accidentally bridge pads with solder that shouldn't be. If you perform this mod you do so of your own accord and with out warranty to its success. If you perform the mod and your receive is very weak, or non existent, one of the lower solder pads on the row of small diodes may be bridged. I had this happen to me and I about died till I figured it out. USE A LOW WATTAGE, FINE TIPPED SOLDERING IRON. !!!SAVE THE PARTS!!!