D22 - 9.1V Zener Diode 2. TR23 (2SC1096) 9 Volts regulator 3. D19 - 5.1 Zener Diode 4. IC4 (TA7222) - Audio Amp 5. TR14 (2SC2029B/10) - Finals 6. TR15 (2SC2028B/20) - Driver 7. Most capacitors over 220uF (like C123, C114 & C112) Check D22, TR23 and C119. If the receive is normal, then possibly any of two (2) faults: 1. microphone/PTT switch and/or the mic cable specifically the wire connected to pin# 3 of the connector; or 2. +8V switching transistor TR21 (2SA733P). November 17, 2010 This is a work in progress, so bare with me. This mod will increase receive strength and dynamic range, resulting in louder, cleaner signals while actually reducing noise levels. All you need to do is to replace the existing first RF amp transistor and SSB detector with a new one which has greater frequency response and lower noise characteristics. Once installed, you might need to do a receiver alignment. Tools needed: soldering iron, solder sucker, or solder wick, pen, small solder, small side cutters, right angle pic (makes removing small parts easier) #2 phillips screw driver The follwing example will be a Cobra 2000 GTL. Parts needed: 1- 2sc2999 High Gain, Low Noise Transistor. 4- 1N6263 Schottky Barrier Diodes 1- Transistor removed from the TR-14 position You can begin by removing both the top and bottom case half's, There is a total of 20 screws that need to be removed (on the Cobra 2000 the woodgrain case needs to be removed first. Take a look at the component side of the radio and find the components TR-14, TR-19, Dl, D2, D21, D22. Take note of the orientation of the transistors (TR's) and note that the flat side faces the rear of the radio, It is important that the new parts be installed the same way, The same holds true for the Diodes (D's) as the stripe must be facing the correct side on the new diodes. We will start with the transistor at position TR-14, this is the Am Detector, You need to unsolder this from the backside of the board; it's easy to find its location on the rear by holding the radio up to a bright light and using a pen to mark one of the legs (or use Sams Photofacts 249). Make sure it's a pen and not a pencil. Once you have the Transistor loose, you can place it aside as you will be using it again in a second. Place the new 2sc2999 transistor in the TR-14 position with the flat side facing the rear of the radio. Bend one or two of the leads to hold the component in place. Flip the radio over and solder the center leg. Then, straighten the two other leads and solder them as well. Move over to the Transistor at TR-19 and remove it. Take the Transistor you removed from the TR-14 position and solder it in place, Again the flat side will face the rear of the radio. This is the ssb detector. You can now replace the diodes at Dl, D2, D21, and D22 with the new 1N6263 diodes. These are low noise diodes that help quiet the natural hiss of the radio. You may want to check the s meter reading as adjust as necessary (generally 100uv for a s9 reading) Early model radios will be marked with a Q instead of a TR, they are the same component. TR-17,Dl, D2,D23, D24 Galaxy DX 33, 44, 55, 66, 73, 77, 88, 99, lib, Pluto, Super Galaxy, Galaxy II, Saturn, SSB, Melaka, RCI2980, Eagle 2000, Connex 3300 (all), Superstar 3600, 3900 (all), Osaka 3900, General Lee, Voyager VR9000, Alan 87, Nortstar Galaxy clones and other radios that use the EPT-3600 series Main Board. TR-18 (Q), Dl, D2, D34, D35 RCI-2950 2970 (non dx) Mirage 2950, Sommerkamp 2000, Galaxy Saturn Turbo, Galaxy DX 22B, Galaxy DX 2527, RCI-2990> Eagle 5000, And other radios that use the EPT-2950 series Main Board. TR-17 (Q), Dl, D2, D30, D31 Galaxy DX 919, 929, 949, 959, 979, DX 2517, DX 2547, DX 45MP, DX 48T, DX 93T, DX 95T, Ranger RG66, RG99, Texas Ranger TR696, TR6300, TR6900 (all), General Grant, Cobra 148f gtl dx+, Connex 4400, 4800, and radios that use the EPT-0929, EPT-0696, and EPT-6900 Main Board COBRA 29 GTL LTD ST WX REMOVE AND REPLACE TR7 D5 D6 AND D24 COBRA 148 GTL OLD: REMOVE AND REPLACE TR14 D1 D2 AND D21 D22. SWAP TR14 AND MOVE THE TRANSISTOR THAT CAME OUT OF TR14 TO TR19 FOR SSB RECEIVE. COBRA 140 GTL 142 GTL REMOVE AND REPLACE TR9 D1 D2 AND D21 D22 COBRA 29 XLR REMOVE AND REPLACE TR1 D1 D2 AND D2O D21 UNIDEN PC66 REMOVE AND REPLACE Q1 D4 D6 COBRA 25 LTD AND GTL, UNIDEN PC66: REMOVE AND REPLACE TR1 D4 AND D6 ON THE COBRA 25 AND UNIDEN 66, TR1 CAN BE FOUND NEAR THE REAR OF THE RADIO IN FRONT OF THE HEATSINK TO THE RIGHT OF THE FINAL AND LEFT OF THE ANTENNA JACK. DIODES CAN BE FOUND IN THE CENTER OF THE RADIO 2.5 INCHES BACK FROM THE FRONT PANEL. YOU WILL SEE A TRIMMER CAN AND A SMALL BOARD STANDING ON EDGE D4 AND D6 ARE IN FRONT OF THESE PARTS. Cobra 138XLR,139XLR,WASHINGTON UPD 858 CHIP AND TRC 457,8 D-10 D-11 D-15 D-16 TR-5 PRESIDENT JACKSON EXPORT TR-11 D19,21 D22,23 President Hr 2510 + Hr 2600 1.) Remove Transistor Q101 (Q1 on the 2600). Both radios use a 2sc945. 2.) Replace Q101 with a 2sc2999 (Q1 on the Hr 2600) Pinout is the same for both transistors. 3.) Replace Noise Blanker Diodes D201 and D202 on Sub Board PB117AA. These are 1N60am diodes. You will have to remove a shield on this board to desolder these diodes. This board seems to be the same in both radios. Note: This is a vertical board that is soldered on the underside of the main board and is to the right of the FM board. 4.) Replace the Am Detector diodes (D111 D112 Hr2510) with better Schottky Barrier diodes. In the Hr 2600, the diodes are labelled D11 & D12. Update: So far, changing Q1 to a 2sc 2999 in the 2600 has had no real effect. So I changed Q6 and Q9 as well. No change in receiver performance has been noted. Next, I will change the noise blanker diodes and the am detector diodes and see what happens. Another update: I have changed the diodes (D11, D12) and put the radio on the air. It seems to be hearing just fine. I had to remove the shield and de-solder on a angle. Frank says it was PAINLESS.....Stay tuned.....Why? Because FRANK SAYS SO!!....GO FRANK!!!