Since owning my first Collins radio (a KWM-1 in 1967) I have kept a file of "fixes" for them, based upon discussions of these on the air with other Collins owners. Several of these "fixes" came from several sources such as magazines, bulletins and my own experience at the workbench. Now with the wonders that the Net has to offer I am placing this collection of repair notes in an appropriate place so that all radio enthusiasts from everywhere can have access to them with just a few keystrokes on the keyboard. No one "owns" this material, so feel free to copy it and distribute it as widely as you want. Enjoy!! 73, H. Michael Crestohl, KH6KD/W1 & VE2XZ Cynthia Reid Crestohl, VE2QF Nahant Massachusetts, U.S.A. mc@shore.net ALL: Service Tip: Repairing PTO Problem: At certain frequencies there was a backlash in the PTO. The dial could be moved plus or minus 1 KC without changing frequency. Close inspection revealed that the play was in the PTO itself and not in the dial mechanism. Solution: 1. Remove PTO mounting screws and dial set screw so the PTO can be pulled free. 2. Remove the collar from the PTO shaft. This normally limits the number of turns of the shaft. 3. Remove the nut securing the PTO rear cover and remove cover. 4. Remove the 2 Phillips screws located on the front of the PTO on either side of the shaft. These screws go all the way through the coil form and are threaded into the rear cover. They are sealed with Glyptal but can be removed with care. 5. Remove the rear cover from the PTO. NOTE: THERE IS A SMALL METAL BEAD THAT FITS BETWEEN THE PTO SHAFT AND THE REAR COVER. IT FITS INTO DIMPLES IN BOTH PARTS. DON'T LOSE IT!!!! 6. The PTO slug moves back and forth on the threaded shaft when it is turned. The slug is not supposed to rotate - there is a spring to prevent this. There is a graphite libricant on the PTO shaft which tends to build up in places causing the slug to rotate instead of moving fore and aft for a slight distance, thus causing play and backlash. Turn the shaft and remove the slug, Clean the excess lubricant off with isopropyl and a Q-tip. 7. Re-assemble the PTO by reversing the procedure. It is possible to do this without disturbing any of the internal wiring of the PTO, hence the calibration is not affected. K9WEH KWM-1: Problem: Emission switch contacts burned causing loss of voltage. Solution: There is an identical unused section on the switch. Wire this (using a short jumper) in parallel with the burnt out contacts without removing any existing wires. KWM-1: Problem: Spurious signal 1KC below regular frequency as reported by other stations. Main signal on 14.050 was S9 and spurious was S1 Solution: Suspected poor grounding on the PTO shaft. Cleaned shaft with Q-tip and Isopropyl. Spurious disappeared. KWM-1: Problem: Original equioment crystal position will not cover the upper part of the 20m phone band. Solution: Installing a 9125 KC crystal in one of the seldom used positions allows coverage from 14.250 to 14.350 W6NIU KWM-1: Problem: Early KWM-1 models were not equipped to run a linear amplifier. Solution: Pick up keyed 265 VDC and run to one of the unused feed-through capacitors to J5 (which receives the power, etc plug). Wire matching plug pin through appropriate resistor to a high resistance, low current relay (total resistance minimum of about 25K) Nount conveniently near rear cover and use this relay to control relay in linear. KWM-1: Problem: Relay contacts intermittent on receive. Solution: Dirty relay contacts. These are very hard to get to on some of the relays. Cut narrow strips of 3by5 card. Wet tip with contact cleaner such as DeOxit and draw through contacts several times. Manually open relay to insert strip and let it close on the strip while drawing through. Follow with dry clean strips until the strip comes out clean. This procedure produces a temporary fix abd must be repeated whenever trouble occurs. W6NIU KWM-1: Problem: Poor drive at either end of the band. Solution: Tune KWM-1 to 14250. Put it in the tune position with sufficient grid drive to produce S3 reading on the meter. Peak the band-pass IF transformer for maximum grid drive, reducing the mic gain control to keep the grid drive around S3. This should correct the problem, assuming that the crystals are of normal activity and when you move from one edge of the band to the other, re-tune the exciter, tune and dip the plate for correct operation. KWM-2/2A: Problem: S-Meter not working on receive. Solution: Replaced V-17 and V-15 (6BN8). KWM-2/2A: To make a quick check of the final tubes (6146) set meter switch to GRID and key mic. If meter goes below 0 - the finals are going soft. Meter needle should stay at 0 or more. KWM-2/2A: Problem: Transmitter dead - was fine the night before. Solution: Examined the disc capacitor mounted over the variable condenser in the PA cage. It was found that heat from the finals melted wax from the disc which dripped down into the variable condenser, shorting it. Cleaned out the wax from the condenser. KWM-2/2A: Problem: Receiver and transmitter do not track properly. Solution: Check diode CR5 (HC7001) and RF Amp V7 (6DC6) KWM-2/2A: Problem: Erratic grid drive - drops very low when transmitting. Solution: Replace V13 (6U8/6DK8). KWM-2/2A: Problem: Transmitter goes into oscillation from a cold start often quite bad when headphones plugged in. This could be stopped if the KWM-2 was bumped sharply. Solution: An intermittent short was found in V16 (6EB8). Replaced V16. KWM-2/2A: Problem: Grid drive very eratic when tuning EXCITER TUNE to try to get a peak reading (EMISSION on TUNE, METER switch on GRID) Solution: Changed driver V8 (6CL6). KWM-2/2A: Problem: Audio leaking on transmit. Solution: Replace C102 (100 uF) in cathode of V16 (6EB8). Very common problem in KWM-2/2A units. W4WCG KWM-2/2A: Service tip: ALC zero adjust. Procedure: Check ALC jack (bias) with VTVM. If this bias exceeds 1.8 Volts plus or minus 20% replace V17 to bring this voltage into the correct limits. Adjust R30 ALC ZERO potentiometer (top of chassis near R45) until the meter indicates zero. KWM-2/2A: Problem: Difficulty in raising the ALC level when changing bands. Solution: Clean the band switch or rotate it a few times to clean the contacts. KWM-2/2A: Problem: On transmit, KWM-2 made a buzzing noise, until the transmitter failed completely. Solution: Found plug-in relay K2 open. Plugged in a new relay and that cured the problem. Note: replacement relays available from: Gould Allied Control, 100 relay Road, Plantsville CT 07479 To replace K2 use catalog # TP163-4C-115VDC coil res 15000. To replace K4 use catalog # TP163-6C-115VDC coil res 9000 These relays can be bought from any large radio stores that sell relays or any nationwide Gould Allied Control distributor KWM-2/2A: Problem: Difficulty in using 6146B finals. 32S-(*) Solution: Apparently the inter-electrode capacitance of the 6146B is different from the 6146 or 6146A finals. This difference in a circuit where RF-inverse feedback is used makes the otherwise insignificant difference very important. KWM-2/2A: Problem: High failure rate of 6CL6 driver and 6U8A tubes 32S-(*) Solution: The 6CL6 driver located in the PA cage tends to run hot. Replace tube shield with IERC TR series. These shields reduce the envelope temperature and give longer life to these tubes. KWM-2/2A: Problem: VOX not working. 32S-(*) Solution: R89 (68K), R112 (68K) on cathode of V11A and R87 (470K) had overheated and burned. Replaced V11 and the three 1/2W resistors with 1W or 2W of same value. W5CRK 32S-(*) Problem: Transmitter cycles on to TRANSMIT when on STANDBY. Solution: Replaced C118 and C119 with premium grade Mylar capacitors. 32S-(*) Problem: Decreased grid drive on top 50KC of each 200KC crystal. Solution: Drive decreased gradually to zero. With meter in GRID position adjust T1 (on top of chassis) for maximum drive while reducing the overall grid drive to the appropriate grid current reading. 32S-(*) Problem: Slow action VOX relay Solution: Replaced V11 (6U8A). 32S-(*) Problem: Erratic grid drive. Solution: Replaced R8 (MIC GAIN) which had become worn and dirty. 32S-(*) Service Tip: Replaced R29 and R30 (4700 Ohm 2W) that had been running hot with a single 2500 Ohm 10W resistor. 32S-(*) Modification: To improve ALC attack times by regulating the screen voltage of V6 (RF Amp) Procedure: As the ALC voltage is biasing off this stage, the screen voltage soars, tending to counteract the ALC effect. A 100K 1/2 Watt resistor in parallel with R38 and a 100K 1 Watt resistor placed from pin 6 of V6 to ground will improve ALC action. 75S-1 Problem: Hum when AF gain control was advanced past half scale. Solution: Replace each of the 6U8A tubes in the receiver with 6EA8. This is a direct replacement. The 6EA8 will give better service as the 6U8s will begin to hum after about 6 to 8 months of use in the receiver. WA4JTI 75S-3 Problem: AGC would not hold after warmup. Solution: Replace V7 (6BA6) second IF amplifier tube. W5SU 75S-3C: Problem: Abrupt drop in signal strength from S9 to very weak with corresponding drop in background noise to near zero. Solution: Found a direct short between the primary and secondary sections of T9 (455Kc) IF Transformer coupling the 1st IF Amp and Q-Mult. Replaced T9. W4FAA 75S-3B Service Tip: To provide a little more gain replace present RF Amp tube with a 6CB6.