07-11-2017, 07:57 PM
Hi Richard.
OK well here we go........ As the set had already been worked on and the detailed voltage readings you gave I thought I'd firstly see if I could trace out the mixer/oscillator. Using the scope I put the probe on the collector on the small board with one transistor T1. there was no results, i should have seen a sine waveform on MW & LW. So a little prod around with the meter I saw the voltage jump when on the base and at this time a low waveform was seen on the scope as i left it connected. Moving from the base further up the print the voltage was different, I then ad a look with the magnifying glass and could see the crack in the print.
Now remember what I said originally..... use ears, eyes, and nose. I actually think this was your original fault as it was away from the "land" where the base connection of the AF117 is soldered to. I then was happy with that area and fitted a known good AF117 at that point to the component side.
Moving on to the IF amp board I removed T2 and fitted another AF117 as what we call a blanket job as I have plenty of "repaired" AF117's so I could then eliminate the transistor and any discrepancies there. Signal was at its collector but nothing on T3 collector, I whipped out the AF114 you had fitted and found a dead short between collector and screen, in other words a tin whisker problem. I'll repair the AF114 though and it will be fine for another 30-40 years. Then I hit problems with the last stage, I'd already seen the can off the IF transformer but wanted to make sure I got results before delving into it.
All the tracing was done with the scope, it is my favourite piece of test equipment and in a case like yours is the best to use. A signal generator would have been useless as you'd not get any further back from the damaged IF transformer. At least I know the set will work once the transformer is fixed. A signal tracer may have been of some help too but in this case I'm sure all will agree in my method.
OK well here we go........ As the set had already been worked on and the detailed voltage readings you gave I thought I'd firstly see if I could trace out the mixer/oscillator. Using the scope I put the probe on the collector on the small board with one transistor T1. there was no results, i should have seen a sine waveform on MW & LW. So a little prod around with the meter I saw the voltage jump when on the base and at this time a low waveform was seen on the scope as i left it connected. Moving from the base further up the print the voltage was different, I then ad a look with the magnifying glass and could see the crack in the print.
Now remember what I said originally..... use ears, eyes, and nose. I actually think this was your original fault as it was away from the "land" where the base connection of the AF117 is soldered to. I then was happy with that area and fitted a known good AF117 at that point to the component side.
Moving on to the IF amp board I removed T2 and fitted another AF117 as what we call a blanket job as I have plenty of "repaired" AF117's so I could then eliminate the transistor and any discrepancies there. Signal was at its collector but nothing on T3 collector, I whipped out the AF114 you had fitted and found a dead short between collector and screen, in other words a tin whisker problem. I'll repair the AF114 though and it will be fine for another 30-40 years. Then I hit problems with the last stage, I'd already seen the can off the IF transformer but wanted to make sure I got results before delving into it.
All the tracing was done with the scope, it is my favourite piece of test equipment and in a case like yours is the best to use. A signal generator would have been useless as you'd not get any further back from the damaged IF transformer. At least I know the set will work once the transformer is fixed. A signal tracer may have been of some help too but in this case I'm sure all will agree in my method.
