TH25AT The Mars & Cap mod for the Kenwood TH-25AT is to remove resistors R18-21. They are located on a panel under the display. This one is a real pain to access but this mod gives transmit coverage from 140-163 Mhz. The TM-721A mod gives trans mit from 142-152 Mhz. ллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллл TH25AT.1 The following information is for the modification of the Kenwood TH-25AT 2 meter handheld. Thanks go to Brad Killebrew, N5LJV for providing this modification. I have not tried this modification so I can't verify that this will work. TH-25AT MARS/CAP MODIFICATION The following modification will allow the TH-25AT to transmit from 141.000 Mhz to 162.995 Mhz. Specifications are guaranteed for the Amateur band only. The transceiver may require realignment of the PLL circuits. 1. Disconnect the battery pack and antenna. 2. Remove the VOLUME, SQUELCH, and TUNING control knobs by pulling them straight up from the top panel. 3. Using a 7mm spanner wrench, remove the nut from the VOLUME control and the nut from the TUNING control. 4. Remove one screw located by the PTT switch. 5. Remove one screw located by the speaker jack. 6. Remove two screws from the battery terminal plate. 7. Carefully pull the front panel up from the transceiver (do not break the wires connected between the front panel and the body of the transceiver). Lay the front panel to the side of the transceiver (keep track of the PTT and F.LOCK covers if they come off). 8. Gently lift the top panel from the transceiver by pulling it forward and then up (the "O" ring on the BNC connector will produce some tension). 9. Rotate the top panel toward the front of the radio to expose the 3/4 x 3/4 inch board. 10. Using a 45 watt (or less) soldering iron that has an isolated or grounded tip, unsolder and remove chip resistors R19 - 21 from the Control Unit (X53-3080-02). 11. Carefully assemble the transceiver by reversing steps 1-9. Pull the BNC connector "O" ring up a little before installing the top panel. 12. Reset the microprocessor by the following the preocedure in the instruction manual (page 16) called CLEARING ALL MEMORY. NOTE: PROTECTING YOUR LICENSE Check the frequency before transmitting to insure you are operating in your authorized transmit range. ллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллл TH25AT.3 TH-25AT MARS/CAP MODIFICATION The following modifications will allow the TH-25AT to transmit from 141.000 to 162.995 MHz. Specifications are guaranteed for the Amateur band only. The transceiver may require realignment of the PLL circuits. 1. Disconnect battery pack and antenna. 2. Remove the volume, squelch and tuning control knobs by pulling them straight up from the top panel. 3. Using a 7mm spanner wrench, remove the nut from the volume control and the nut from the tuning control. 4. Remove one screw from the back of the radio, by the PTT switch. 5. Remove one screw near the speaker jack. 6. Remove two screws from the battery terminal plate: --- remove ---- / \ +---------------------+ [ 0 0 [ [ [ [ +------+ [ [ [ [ [ [ +------+ [ [ [ [ O O [ +---------------------+ 7. Carefully pull the front panel up from the transceiver (do not break the wires connected between the front panel and the body of the transceiver). Lay the front panel to the side of the transceiver (keep track of the PTT and F.LOCK covers if they come off). 8. Gently lift the top panel from the transceiver by pulling it forward and then up (the O-ring on the BNC connector will produce some tension). 9. Rotate the top panel toward the front of the radio to expose the 3/4 x 3/4" board. 10. Using a 45 watt (or less) soldering iron that has an isolated or grounded tip, unsolder and remove chip resistors R19, R20 and R21 from the control unit (X53-3080-02). 11. Carefully reassemble the transceiver by reversing steps 1-9. Pull the BNC connector O-ring up a little before installing the top panel. 12. Reset the microprocessor by following the procedure in the instruction manual (p. 16) called CLEARING ALL MEMORY. Disclaimers: The source of this information is unknown and not personally verified. It is illegal to transmit outside the ham bands with this equipment. Frank W9MKV reid@gold.bacs.indiana.edu ллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллл Subject: KENWOOD TH-25/45 OUT OF BANAD MODIFICATIONS Here are some mods for the TH-25AT and the TH-45AT. Please note that I do not encourage transmitting on a frequency for which you do not have a license, nor do I encourage transmitting on a non-amateur frequency without FCC type accepted equipment (in the United States). First let me recommend that you buy the service manuals for these radios. The service manual is not expensive (about $15 I think) and it will greatly help you in performing these modifications. Look at the schematic for your radio. In the lower left hand corner is an IC labled IC2. This is an ASIC microprocessor. At the lower right hand corner of this uP are several diodes and pull-up/pull-down resistors. They are D4, D3, R19, R18, R28, R20, R21, R22, R25, R26, and a couple of resistors that are not even on the schematic that attach to B2 (pin 51 on IC2) and B3 (pin 50 on IC2). The TH-45AT schematic shows R23 on the ASIC uP pin B2. The schematic for the TH-25AT shows: R18-R21 R25 R26,27 R28 R36 TH-25A M,M2 -12 O X X X X TH-25A M3,M4,X -23 O X X O X TH-25AT K -11 O O X X X TH-25AT M,M2 -12 O X X X X TH-25E T -52 X X O O O TH-25E W -62 X O O O O And the schematic for the TH-45AT shows: R19-R21 R22 R23 R25 R26,27 R28 R36 TH-45A M1,M2,X -21 O O O X X O X TH-45A M3,M4 -22 O X O X X X X TH-45AT K -10 O X O X X O X TH-45AT M1,M2 -21 O O O X X O X TH-45AT M3,M4 -22 O X O X X X X TH-45E T -51 X O X X O X O TH-45E W -61 X O X O O O O where O means USED, and X means NOT USED. Some of the above codes are: K USA T England X Australia M Other Areas These components are found on the flexible circuit board under the display. To get to them, take the radio apart. Some unsoldering of obvious grounding wires may be necessary. You will see where the flexible circuit board plugs into a socket on the main circuit board. Before unplugging it, make sure you know what's in the memories, because they will be lost. Unplug the flexible circuit board and unfold it so that the components are accesable. One of the fold-out parts of the flexible board will look something like this: +----------------+ ! R R R D3 R R ! ! 2 2 2 7 2 ! ! 5 3 2 1 ! ! ! ! R O O R20! The O's are solder pads. ! 2 O O R19! ! 6 O O R18! ! O O R28! ! ! ! R ! ! D4 6 ! ! +-------+ ! ! ! ! The fold out board is actually square, but with only characters for graphics, I couldn't draw it that way. On both radios, R36 is for the European tone burst to "whistle up" repeaters. On both radios, D4 is for selecting the type of display. With D4 in, the display is normal. With D4 removed, the display is a channel display. D3 is for selecting VHF or UHF. With D4 in, the radio thinks its a VHF radio. With D4 removed, the radio thinks its a UHF radio. Don't change this on your radio. TH25AT.6 On the TH-25AT: (All frequencies given in MHz.) R22 in R28 out This is how the radio is delivered in the USA. TX 144-1, 141-163 (I think). R22 out R28 in The radio tunes from 142-151. This may be the modification given to US MARS members. I don't remember where the unit will transmit. It may or may not transmit outside the range from 144-148. R22 in R28 in The radio tunes only from 144-148. R22 out R28 out Frequencies may be selected from 100-200 MHz (on the display only - your PLL will not lock up in this entire range). In addition, TX is possible where your PLL locks up. R25 out Removing R25 disables automatic offset selection. R23 and R24 are used for selecting the step size for tuning. I can't remember which positions are for which step sizes, and alas I didn't write down what I found. If you want to play with this, go ahead. TH25AT.11 On the TH-45AT: (All frequencies are given in MHz.) R18 in R28 in This is how the radio is delivered in the USA. The radio covers 438-450 MHz. R18 in R20 out The radio is prohibited from tuning outside 440-450 MHz. R18 out R28 in The radio will only tune from 215-230 MHz. Note that the PLL would not lock up! (What did you expect?) Could it be possible that Kenwood originally planned a 220 version of this radio, but then scrapped their plans? R18 out R28 out The radio will tune from 200-500 MHz (on the display only - your PLL will not lock up over this entire range). Transmitting is possible anywhere your PLL will lock up. I have found a quick and easy way to retune your PLL (in the TH45-AT) with a minimum of test equipment. All you need is a scope and a small tuning tool. First, take off the battery pack holder plate. Then, remove the silvery sticker covering the tuning pot access holes. If the radio is positioned on its back, with the top folded over so that the touch tone pad is also facing down, the test point you want (TP1) is on the bottom half of the radio, near the center (left to right), and close to the battery; the tuning pot you want (TC1) is on the bottom, and closest to the PTT switch. Under no circumstances change the tuning of TC51. This is used to calibrate the output of the radio with the display the radio is giving; you don't want to mess with it. Once again, the Service Manual makes it very clear where these points are, if you are having trouble with my descriptions. On with retuning the PLL. With the radio on, and receiving, monitor the voltage and the waveform on test point TC1. Tune the radio DOWNWARDS in frequency until the PLL unlocks. Note that the radio will beep when this happens, and the waveform on TP1 will change. Tune the radio about 1 MHz higher so that the PLL locks up again, and note the voltage on the testpoint, TP1. Now, tune the radio to the LOWEST frequency that you want to be able to receive. Adjust TC1 until the voltage on the test point TP1 is the same as what was noted earlier. Button the radio back up, and you're done. You will not be able to tune the PLL to any range you want. There are limits. On my radio, I have been able to retune the radio so that I can recieve from 439.2-468.6 MHz with a set of batteries fresh out of the charger. The tuning range will probably diminish as the battery voltage decreases. I have not retuned the PLL on my 2m HT, but I'd imagine the same technique will prove fruitful. I may have some more information on these radios someplace. If I can find it, I will add to this posting, and post it again with the updated information. Enjoy. Kenneth J. Hendrickson N8DGN Note: I haven't tried or verified these mods, proceed at your own risk! WA2ISE ллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллллл Here is the function of the diodes and pull up or pull down resistors (for both the TH-25AT and the TH-45AT unless otherwise specified): D4 selects the display type. installed: channel display removed: normal frequency display You probably don't want to install this. R6 is the pullup resistor for D4. Do not remove it, so that if D4 is removed, pin 44 of IC2 will be properly pulled up. D3 selects VHF or UHF. installed: VHF removed: UHF You definitely don't want to change this! R7 is the pullup resistor for D3. Do not remove it, so that if D3 is removed, pin 45 of IC2 will be properly pulled up. R25 selects automatic offset selection. installed: automatic offset selection enabled. removed: automatic offset selection disabled. R25 seems to have no effect on the TH-45AT. R23,27 frequency selection step size. Frequency selection step sizes is only known for TH-45AT. R23 R27 frequency selection step sizes: --- --- --------- --------- ---- ------ out out 5 and 10 kHz in out 5 and 25 kHz (TH-45AT default) out in 5 and 12.5 kHz (author's preference) in in 10 and 20 kHz R23 probably has no effect on the TH-25AT. I never checked. I was quite satisfied with the 5 and 10 kHz step sizes for the TH-25AT. I never tried changing R27 to see what would happen. R24 ? something with the CTCSS tone ? installed: When a TX offset is selected, the CTCSS tone is always transmitted. The TONE button does not work correctly. When the TONE button is depressed, the display goes to 430.000 c, and nothing seems to work. (A "c" is displayed in the channel number position.) The action of the TH-25AT is unknown. removed: CTCSS tone selection works correctly. Both the TH-25AT and the TH-45AT are delivered this way. You probably don't want to install this. R19 function unknown. R19 is not installed in the European version. R20 function unknown. R20 is not installed in the European version. R21 function unknown. R21 is not installed in the European version. R19, R20, and R21 are all in parallel. Thus, if any of them is installed, it is like all of them are installed. R26 function unknown. R26 is installed in the European version. On the TH-25AT: R22,28 select RX and TX frequency range. R22 R28 RX range TX range --- --- -- ----- -- ----- in out 144-148 141-163 (USA default) in in 144-148 144-148 out out 100-200 100-200 (only where your PLL locks up.) out in 142-151 ???-??? R18 exact function unknown. installed: as delivered in USA. removed: TX disabled from 146-148. The RX and TX frequency range based on R22 and R28 are unknown if R18 is removed. On the TH-45AT: R18,28 select RX and TX frequency range. R18 R28 RX range TX range --- --- -- ----- -- ----- in out 440-450 440-450 in in 438-450 438-450 (USA default) out out 200-500 200-500 (only where your PLL locks up.) out in 215-230 215-230? (PLL won't lock up.) R22 TX offset selection installed: 1.6 MHz offset (perhaps for 220, or Europe) removed: 5 MHz offset (USA default) --------------------------------------------------------------------- PLL adjustment --- ---------- I have found a quick and easy way to retune your PLL (in the TH45-AT) with a minimum of test equipment. All you need is a scope and a small tuning tool. First, take off the battery pack holder plate. Then, remove the silvery sticker covering the tuning pot access holes. If the radio is positioned on its back, with the top folded over so that the touch tone pad is also facing down, the test point you want (TP1) is on the bottom half of the radio, near the center (left to right), and close to the battery; the tuning pot you want (TC1) is on the bottom, and closest to the PTT switch. Under no circumstances change the tuning of TC51. This is used to calibrate the output of the radio with the display the radio is giving; you don't want to mess with it. Once again, the Service Manual makes it very clear where these points are, if you are having trouble with my descriptions. On with retuning the PLL. With the radio on, and receiving, monitor the voltage and the waveform on test point TC1. Tune the radio DOWNWARDS in frequency until the PLL unlocks. Note that the radio will beep when this happens, and the waveform on TP1 will change. Tune the radio about 1 MHz higher so that the PLL locks up again, and note the voltage on the testpoint, TP1. Now, tune the radio to the LOWEST frequency that you want to be able to receive. (Be very careful when you adjust TC1. If you are not careful, you could break TC1 loose. This will cause your radio to have microphonics. Mechanical vibrations will change the value of this capacitor, and thus change the tuning on the PLL. If you encounter this problem, you can repair it by dripping wax through the small hole onto TC1, or by replacing TC1. It is of course better not to break it in the first place.) Adjust TC1 until the voltage on the test point TP1 is the same as what was noted earlier. Button the radio back up, and you're done. You will not be able to tune the PLL to any range you want. There are limits. On my radio, I have been able to retune the radio so that I can recieve from 439.2-468.6 MHz with a set of batteries fresh out of the charger. The tuning range will probably diminish as the battery voltage decreases. I have not retuned the PLL on my 2m HT, but I'd imagine the same technique will prove fruitful. --------------------------------------------------------------------- In the rare case that original ideas Kenneth J. Hendrickson N8DGN are found here, I am responsible. Owen W328, E. Lansing, MI 48825 Internet: kjh@pollux.usc.edu UUCP: ...!uunet!pollux!kjh ======================================================================= Date: 10 Jun 89 19:41:32 GMT Subject: Kenwood HT-45A mods? ( and TH-25AT ) Ok, I've promised it for a long time and now it's time to live up to my promises. Here are some mods for the TH-25AT and the TH-45AT. Please note that I do not encourage transmitting on a frequency for which you do not have a license, nor do I encourage transmitting on a non-amateur frequency without FCC type accepted equipment (in the United States). Lament: when are the Japanese going to produce a 440 FM HT for the US market that has receive coverage outside the US amateur band? Lord knows that there's a market for it - there's MONEY to be made. First let me recommend that you buy the service manuals for these radios. The service manual is not expensive (about $15 I think) and it will greatly help you in performing these modifications. Look at the schematic for your radio. In the lower left hand corner is an IC labled IC2. This is an ASIC microprocessor. At the lower right hand corner of this uP are several diodes and pull-up/pull-down resistors. They are D4, D3, R19, R18, R28, R20, R21, R22, R25, R26, and a couple of resistors that are not even on the schematic that attach to B2 (pin 51 on IC2) and B3 (pin 50 on IC2). The TH-45AT schematic shows R23 on the ASIC uP pin B2. The schematic for the TH-25AT shows: R18-R21 R25 R26,27 R28 R36 TH-25A M,M2 -12 O X X X X TH-25A M3,M4,X -23 O X X O X TH-25AT K -11 O O X X X TH-25AT M,M2 -12 O X X X X TH-25E T -52 X X O O O TH-25E W -62 X O O O O And the schematic for the TH-45AT shows: R19-R21 R22 R23 R25 R26,27 R28 R36 TH-45A M1,M2,X -21 O O O X X O X TH-45A M3,M4 -22 O X O X X X X TH-45AT K -10 O X O X X O X TH-45AT M1,M2 -21 O O O X X O X TH-45AT M3,M4 -22 O X O X X X X TH-45E T -51 X O X X O X O TH-45E W -61 X O X O O O O where O means USED, and X means NOT USED. Some of the above codes are: K USA T England X Australia M Other Areas These components are found on the flexible circuit board under the display. To get to them, take the radio apart. Some unsoldering of obvious grounding wires may be necessary. You will see where the flexible circuit board plugs into a socket on the main circuit board. Before unplugging it, make sure you know what's in the memories, because they will be lost. Unplug the flexible circuit board and unfold it so that the components are accesable. One of the fold-out parts of the flexible board will look something like this: +----------------+ | R R R D3 R R | | 2 2 2 7 2 | | 5 3 2 1 | | | | R O O R20| The O's are solder pads. | 2 O O R19| | 6 O O R18| | O O R28| | | | R | | D4 6 | | +-------+ | | | | The fold out board is actually square, but with only characters for graphics, I couldn't draw it that way. On both radios, R36 is for the European tone burst to "whistle up" repeaters. On both radios, D4 is for selecting the type of display. With D4 in, the display is normal. With D4 removed, the display is a channel display. D3 is for selecting VHF or UHF. With D4 in, the radio thinks its a VHF radio. With D4 removed, the radio thinks its a UHF radio. Don't change this on your radio. On the TH-25AT: (All frequencies given in MHz.) R22 in R28 out This is how the radio is delivered in the USA. TX 144-148, RX 141-163 (I think). R22 out R28 in The radio tunes from 142-151. This may be the modification given to US MARS members. I don't remember where the unit will transmit. It may or may not transmit outside the range from 144-148. R22 in R28 in The radio tunes only from 144-148. R22 out R28 out Frequencies may be selected from 100-200 MHz (on the display only - your PLL will not lock up in this entire range). In addition, TX is possible where your PLL locks up. R25 out Removing R25 disables automatic offset selection. R23 and R24 are used for selecting the step size for tuning. I can't remember which positions are for which step sizes, and alas I didn't write down what I found. If you want to play with this, go ahead. On the TH-45AT: (All frequencies are given in MHz.) R18 in R28 in This is how the radio is delivered in the USA. The radio covers 438-450 MHz. R18 in R20 out The radio is prohibited from tuning outside 440-450 MHz. R18 out R28 in The radio will only tune from 215-230 MHz. Note that the PLL would not lock up! (What did you expect?) Could it be possible that Kenwood originally planned a 220 version of this radio, but then scrapped their plans? R18 out R28 out The radio will tune from 200-500 MHz (on the display only - your PLL will not lock up over this entire range). Transmitting is possible anywhere your PLL will lock up. I have found a quick and easy way to retune your PLL (in the TH45-AT) with a minimum of test equipment. All you need is a scope and a small tuning tool. First, take off the battery pack holder plate. Then, remove the silvery sticker covering the tuning pot access holes. If the radio is positioned on its back, with the top folded over so that the touch tone pad is also facing down, the test point you want (TP1) is on the bottom half of the radio, near the center (left to right), and close to the battery; the tuning pot you want (TC1) is on the bottom, and closest to the PTT switch. Under no circumstances change the tuning of TC51. This is used to calibrate the output of the radio with the display the radio is giving; you don't want to mess with it. Once again, the Service Manual makes it very clear where these points are, if you are having trouble with my descriptions. On with retuning the PLL. With the radio on, and receiving, monitor the voltage and the waveform on test point TC1. Tune the radio DOWNWARDS in frequency until the PLL unlocks. Note that the radio will beep when this happens, and the waveform on TP1 will change. Tune the radio about 1 MHz higher so that the PLL locks up again, and note the voltage on the testpoint, TP1. Now, tune the radio to the LOWEST frequency that you want to be able to receive. Adjust TC1 until the voltage on the test point TP1 is the same as what was noted earlier. Button the radio back up, and you're done. You will not be able to tune the PLL to any range you want. There are limits. On my radio, I have been able to retune the radio so that I can recieve from 439.2-468.6 MHz with a set of batteries fresh out of the charger. The tuning range will probably diminish as the battery voltage decreases. I have not retuned the PLL on my 2m HT, but I'd imagine the same technique will prove fruitful. I may have some more information on these radios someplace. If I can find it, I will add to this posting, and post it again with the updated information. Enjoy. In the rare case that original ideas Kenneth J. Hendrickson N8DGN are found here, I am responsible. Owen W328, E. Lansing, MI 48825 Internet: hendrick@frith.egr.msu.edu UUCP: ...!frith!hendrick [ Editor Note: With my radio, I had to remove the following resistors to enable full rx/tx: R19, R20, R21, R22, R28 de VE3PZR ] ====================================================================== ============================================================================= Newsgroups: rec.radio.amateur.misc Subject: TH25 and 45 automatic power off defeat Keywords: mod Message-ID: <1991Dec10.044456.26533@cbfsb.att.com> Date: 10 Dec 91 04:44:56 GMT Sender: news@cbfsb.att.com Organization: AT&T Bell Laboratories Lines: 57 copied from packet: Msg# TSF Size #Rd Date Time From MsgID To 8733 BF 2759 0 08-Dec 0330 KD2EJ 28521_WB2QJA INFO@ALLBBS () Sb: TH-25-45AT AUTO POWER OFF. SB-939 TH-25/45AT Automatic Power OFF Function 8-02-88 Some users of the TH-25AT/45AT have expressed a desire to defeat the automatic power off function. The following modification will explain how to do this. It should be noted that this modification does not effect the battery saver function. Required Part: Diode Kenwood Part #1SS133 1. Disconnect the battery pack and antenna. 2. Remove the Volume, Squelch, and Tuning Control knobs by pulling them straight up from the top panel. 3. Using a 7mm spanner wrench, remove the nut from the volume control and the nut from the tuning control. 4. Remove one screw located by the PTT switch. 5. ReMOve one screw located by the speaker jack. 6. Remove two screws from the battery terminal plate. 7. Carefully pull the front panel up from the transceiver (do not break the wires connected between the front panel and the body of the transceiver.) Lay the front panel to the side of the transceiver (Keep track of the F.LOCK cover if it comes off.) 8. Remove the PTT cover. 9. Remove one screw from the PTT switch unit. 10. Gently lift the top panel from the transceiver by pulling it forward and then up (the "O" ring on the BNC connector will produce some tension.) 11. Carefully unfold the flex Printed Circuit Board (PCB) to expose IC2. 12. Using a 45 watt (or less) soldering iron that has an isolated or grounded tip, add a diode between pins 23 and 58 of IC2. 13. Carefully assemble the transceiver by reversing step 1-11. Pull the BNC connector "O" ring up a little before installing the top panel. 14. Reset the microprocessor by following the procedure in the instruction manual (page 16) called CLEARING ALL MEMORY. This is an optional change that is not covered under warranty. Time required for this modification is 1 hour or less. SYSOP NOTES: Later versions of the TH-25/45AT came with a programmable defeat for the Auto power off function. Do not install this modification if your manual provides a procedure for turning the power off function off! Step 11 tells you to carefully unfold the flexible pc board. It is extremely important that you do not try and bend the board in a direction that is opposite from its current bend. To do so will break the board or the foil traces inside the board! (c) 121589TKC ============================================================================= Msg Nr. : 135517 Da : IW3GRX Per : MOD Tipo/status : PN Data/ora : 0108/1657 Dimensione : 7721 Bid (Mid) : 4445_IW3GRX Titolo : Alcune modifiche per il TH25 ************************************************************************** TH-25AT TH-45AT Ok, I've promised it for a long time and now it's time to live up to my promises. Here are some mods for the TH-25AT and the TH-45AT. Please note that I do not encourage transmitting on a frequency for which you do not have a license, nor do I encourage transmitting on a non-amateur frequency without FCC type accepted equipment (in the United States). Lament: when are the Japanese going to produce a 440 FM HT for the US market that has receive coverage outside the US amateur band? Lord knows that there's a market for it - there's MONEY to be made. First let me recommend that you buy the service manuals for these radios. The service manual is not expensive (about $15 I think) and it will greatly help you in performing these modifications. Look at the schematic for your radio. In the lower left hand corner is an IC labled IC2. This is an ASIC microprocessor. At the lower right hand corner of this uP are several diodes and pull-up/pull-down resistors. They are D4, D3, R19, R18, R28, R20, R21, R22, R25, R26, and a couple of resistors that are not even on the schematic that attach to B2 (pin 51 on IC2) and B3 (pin 50 on IC2). The TH-45AT schematic shows R23 on the ASIC uP pin B2. The schematic for the TH-25AT shows: R18-R21 R25 R26,27 R28 R36 TH-25A M,M2 -12 O X X X X TH-25A M3,M4,X -23 O X X O X TH-25AT K -11 O O X X X TH-25AT M,M2 -12 O X X X X TH-25E T -52 X X O O O TH-25E W -62 X O O O O And the schematic for the TH-45AT shows: R19-R21 R22 R23 R25 R26,27 R28 R36 TH-45A M1,M2,X -21 O O O X X O X TH-45A M3,M4 -22 O X O X X X X TH-45AT K -10 O X O X X O X TH-45AT M1,M2 -21 O O O X X O X TH-45AT M3,M4 -22 O X O X X X X TH-45E T -51 X O X X O X O TH-45E W -61 X O X O O O O where O means USED, and X means NOT USED. Some of the above codes are: K USA T England X Australia M Other Areas These components are found on the flexible circuit board under the display. To get to them, take the radio apart. Some unsoldering of obvious grounding wires may be necessary. You will see where the flexible circuit board plugs into a socket on the main circuit board. Before unplugging it, make sure you know what's in the memories, because they will be lost. Unplug the flexible circuit board and unfold it so that the components are accesable. One of the fold-out parts of the flexible board will look something like this: +----------------+ | R R R D3 R R | | 2 2 2 7 2 | | 5 3 2 1 | | | | R O O R20| The O's are solder pads. | 2 O O R19| | 6 O O R18| | O O R28| | | | R | | D4 6 | | +-------+ | | | | The fold out board is actually square, but with only characters for graphics, I couldn't draw it that way. On both radios, R36 is for the European tone burst to "whistle up" repeaters. On both radios, D4 is for selecting the type of display. With D4 in, the display is normal. With D4 removed, the display is a channel display. D3 is for selecting VHF or UHF. With D4 in, the radio thinks its a VHF radio. With D4 removed, the radio thinks its a UHF radio. Don't change this on your radio. On the TH-25AT: (All frequencies given in MHz.) R22 in R28 out This is how the radio is delivered in the USA. TX 144-148, RX 141-163 (I think). R22 out R28 in The radio tunes from 142-151. This may be the modification given to US MARS members. I don't remember where the unit will transmit. It may or may not transmit outside the range from 144-148. R22 in R28 in The radio tunes only from 144-148. R22 out R28 out Frequencies may be selected from 100-200 MHz (on the display only - your PLL will not lock up in this entire range). In addition, TX is possible where your PLL locks up. R25 out Removing R25 disables automatic offset selection. R23 and R24 are used for selecting the step size for tuning. I can't remember which positions are for which step sizes, and alas I didn't write down what I found. If you want to play with this, go ahead. On the TH-45AT: (All frequencies are given in MHz.) R18 in R28 in This is how the radio is delivered in the USA. The radio covers 438-450 MHz. R18 in R20 out The radio is prohibited from tuning outside 440-450 MHz. R18 out R28 in The radio will only tune from 215-230 MHz. Note that the PLL would not lock up! (What did you expect?) Could it be possible that Kenwood originally planned a 220 version of this radio, but then scrapped their plans? R18 out R28 out The radio will tune from 200-500 MHz (on the display only - your PLL will not lock up over this entire range). Transmitting is possible anywhere your PLL will lock up. I have found a quick and easy way to retune your PLL (in the TH45-AT) with a minimum of test equipment. All you need is a scope and a small tuning tool. First, take off the battery pack holder plate. Then, remove the silvery sticker covering the tuning pot access holes. If the radio is positioned on its back, with the top folded over so that the touch tone pad is also facing down, the test point you want (TP1) is on the bottom half of the radio, near the center (left to right), and close to the battery; the tuning pot you want (TC1) is on the bottom, and closest to the PTT switch. Under no circumstances change the tuning of TC51. This is used to calibrate the output of the radio with the display the radio is giving; you don't want to mess with it. Once again, the Service Manual makes it very clear where these points are, if you are having trouble with my descriptions. On with retuning the PLL. With the radio on, and receiving, monitor the voltage and the waveform on test point TC1. Tune the radio DOWNWARDS in frequency until the PLL unlocks. Note that the radio will beep when this happens, and the waveform on TP1 will change. Tune the radio about 1 MHz higher so that the PLL locks up again, and note the voltage on the testpoint, TP1. Now, tune the radio to the LOWEST frequency that you want to be able to receive. Adjust TC1 until the voltage on the test point TP1 is the same as what was noted earlier. Button the radio back up, and you're done. You will not be able to tune the PLL to any range you want. There are limits. On my radio, I have been able to retune the radio so that I can recieve from 439.2-468.6 MHz with a set of batteries fresh out of the charger. The tuning range will probably diminish as the battery voltage decreases. I have not retuned the PLL on my 2m HT, but I'd imagine the same technique will prove fruitful. I may have some more information on these radios someplace. If I can find it, I will add to this posting, and post it again with the updated information. Enjoy. ----> Abortion is murder; Affirmative Action is discrimination. <---- In the rare case that original ideas Kenneth J. Hendrickson N8DGN are found here, I am responsible. Owen W328, E. Lansing, MI 48825 Internet: hendrick@frith.egr.msu.edu UUCP: ...!frith!hendrick *****************************************************************************