Got a Cobra 142 GTL base on the desk today.
Issue(s):
1. Squeals through speaker when Transmitting.
2. Clarifier not centered at 12 o'clock.
3. Receive weak in all modes.
4. Both sidebands sound terrible.
Evaluation:
1. The external speaker jack on the back of the radio is loose, which causes a squeal through speaker when Transmitting. Fixed by tightening up external speaker/PA speaker screws.
2. PLL offset oscillators and the carrier offset oscillators are way off. Clarifier has been unlocked (not the right way though) and a 4.7uh choke tied off to the varacator diode. Also, they didn't complete the unlock procedure fully. They never removed the ground wire from clarifier to small board with switches on it. And they had the 2 wires backwards. Fixed by putting clarifier back stock, aligning all oscillators, then unlocking clarifier my way without the choke, then centered oscillators for 12 o'clock clarifier position.
3. Receive is weak due to oscillators being out of whack and the receive IF cans have been messed with. Fixed by alignment.
4. SSB sounded garbled and oscope pattern didn't look right. Fixed by replacing TR32 that someone yanked out.
Output before:
Variable on back of radio, goes from 0 (yuk) watts up to 6 watts.
PEP swing - 14w
Peak swing - 10w
Average swing - 6w
Output after:
PEP swing - 20w
Peak swing - 14w
Average swing - 9w
Clarifier slides from 27.205 center slot down to 27.2015 and up to 27.2073.
Now I'm perfectly fine with this slide range, but the owner is gonna probably want more. Which resistor controls the slide range on these PC-385 chassis? I know R175 in the 2000's and 148's you can swap out for a different value to increase the range, not sure about the 142 though.
