18-05-2013, 10:03 PM
A few squirts of contact cleaner has freed up the switches. Still no AM/FM.
Checking back on AM one BF was O/C, swapped, all appeared OK but no sound.
Checked for LO using 7600, LW,MW and SW all OK. Touching I/P to front end at the Fet, brought in MW stations, also at the tuned L, dead at the Antenna I/P side though, all switches are OK Rather Odd !!!!!!!! Couldn't find anything immediately, this is going to be a bit of a pain I reckon. On the FM side dead in front of the stereo demod. IC (MC1305P) doesn't appear to be drawing any current. (Just happened to have a couple of MC1305Ps in the goodies box (As you do !!!!!)) .
Swapped it..... SOUND albeit distorted. swapped it for another with same result.
Getting Hum on both channels (Previously Intermittent) and one of the PAs is getting a bit warm. A quick check on an emitter R showed it was passing a few Amps. I noticed that part of the trimmer pot for the quiescent current had rusted away. It was 470Ohms, nearest in the goodies box 1K Ceramic. Swapped them in both channels and fitted a 1K in parallel.
Cool now without hum (Previous cap change was not necessary)
Everything is distorted now AM/FM and external Audio I/P.
A good time to break off and have a drink or 3 and think about what has happened.
Mike
Checking back on AM one BF was O/C, swapped, all appeared OK but no sound.
Checked for LO using 7600, LW,MW and SW all OK. Touching I/P to front end at the Fet, brought in MW stations, also at the tuned L, dead at the Antenna I/P side though, all switches are OK Rather Odd !!!!!!!! Couldn't find anything immediately, this is going to be a bit of a pain I reckon. On the FM side dead in front of the stereo demod. IC (MC1305P) doesn't appear to be drawing any current. (Just happened to have a couple of MC1305Ps in the goodies box (As you do !!!!!)) .
Swapped it..... SOUND albeit distorted. swapped it for another with same result.
Getting Hum on both channels (Previously Intermittent) and one of the PAs is getting a bit warm. A quick check on an emitter R showed it was passing a few Amps. I noticed that part of the trimmer pot for the quiescent current had rusted away. It was 470Ohms, nearest in the goodies box 1K Ceramic. Swapped them in both channels and fitted a 1K in parallel.
Cool now without hum (Previous cap change was not necessary)
Everything is distorted now AM/FM and external Audio I/P.
A good time to break off and have a drink or 3 and think about what has happened.
Mike
