Harris MW-5 Service Bulletin Download Page 1 | Manualshive

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Summary of Contents for MW-5

Page 1: ...ct the audio lines from the transmitter Carefully observe the actions of the plate current and power output meter while depressing the HIGH VOLTAGE ON button If the plate current meter in the isolated plate section momentarily deflects upscale the overload current is being conducted through the modulator section the PA and modulator are in series with the plate current meter between the modulator ...

Page 2: ...tifiers typically measure open or a high resistance in the forward direction This is because the forward voltage drop of the rectifier is often greater than the battery voltage of the ohmeter You should never measure resistance less than infinity in the negative direction B DC Overloads Plate current meter deflects power output meter does not 1 Complete loss of PA grid drive The PA tube developes ...

Page 3: ...A2Al Ul defective Check for squarewave output at the carrier frequency at terminal 8 of the oscillator board h 1A2Al Q4 shorted Check 1A2Al R23 and R24 for over dissipation Causes for zero IPA current would be a No drive to the IPA input Check continuity from pin 3 of the oscillator board to pin 1 of the IPA module b 1A2A3 Fl blown and probably Ql and Q2 on the IPA module are shorted Other than a ...

Page 4: ...n the audio driver Measure the voltage at lAlTBl 21 to determine if the bias supply is working Q2 on the Audio Driver may be removed at this time since its only purpose is to boost positive modulation capabilities The voltage drop across 1AlA3 CR8 CR11 should be about 230 volts with the filaments on Normally the modulator grid voltage will remain at 230 volts with the modulator screen circuit brea...

Page 5: ...ted Check for 39V at cathode with the filaments on 1AlA3 Q2 shorted It should already have been removed lAlAl Q5 shorted The collector voltage of QS is approximately 4 volts in its normal on stat e and 8 volts in its off state with just the filaments on The off state voltage increases to 10 volts wi t h the screen supply energized Q5 should be o ff with terminal K grounded lAlAl Q3 shorted Measure...

Page 6: ...DM signal at pin 10 of the audio driver with a scope The signal should closely resemble that shown on the PDM and audio driver schematic If it does not trace the signal back through the audio driver and PDM boards Components that typically degrade the slope of the PDM signal are leaky zener diodes coupling the PDM signal and the transistors which amplify it The slope of the PDM signal is important...

Page 7: ...PDM filter coils 1Ll 1L3 A change in these coils is usually visible 3 Check the PDM frequency It should be in the range of 70 85 Khz Changes within this range have an effect on 10 Khz distortion noise and a relatively small effect on response 4 Make substitutions in the PDM filter for 1C5 lCB and lCl0 Improper PDM filtering will affect high frequency response 5 Poor antenna sidebands can also affe...

Page 8: ...ecks of the screen and cathode circuits may also be made b If the modulator bias is over 200 volts negative when the high voltage is on the PDM and Audio Driver are holding the modulator tube cut off Remove any connection at 1TB2 9 EBS Phasor Off which may be holding the PDM Off Aside from the EBS Phasor Off and the adjustment of the power controls components likely to cause the modulator bias to ...

Page 9: ...ustment Turn the high and low power contr ols to minimum Turn the transmitter off and r emove then invert the directional coupler The reflected portion will now sample forward power Switch the power output meter to reflected Turn the transmitter on and gradually turn the power output up until 400 watts is regi stered on the meter The VSWR circuit should trip at this point If adjustment is necessar...

Page 10: ...blue CTS or Mallory potentiometers as are used for the dissipation 10 and carrier shift controls The flat CTS and Mallory potentiometers were used for high and low power controls in early productions therefore these potentiometers will not be printed circuit board compatible with some older MW 5 transmitters Check to see what your transmitter uses before ordering this part Part Number 550 0976 000...

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