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|Here I was tonight gathering up the loose odds and ends of a nice old Emerson ED354 that I basically had completed last fall. It was awaiting cabinet work so it sat all winter.
One of my customers who tells me he does furniture refinishing offered to help do a couple cabinets for me at $25 each... so I gave him two to do.
Well he brought them back today ( not my level of quality... but hey for $25 I couldn't make him feel bad) and anyway...that's what prompted the need now for me to get this Emerson reassembled.
I saw that it still needed a new power cord though but everything else had been done. So I hooked up a temp power cord and fired it up as a test while my iron warmed up to solder on that new cord.
Well it came to life quickly and sounded beautiful... so I shut it off and put on the new AC cord.
So I quickly checked that everything is in order.. antenna connection... B+ ...yes, yes yes..
Fire up my scope to see the oscillator... sure enough that's fine!
Fire up the signal generator to 455khz modulated... connect it to the ext. antenna terminal lug on the loop antenna ... and boom!.. plenty strong tone!
Okay I've got IFs aligned and signal getting ALL the way through right from the antenna.
What the heck kind of a problem is this I thought?
So I now changed the signal generator to 1-Mhz with modulation and connected it right to the antenna... and sure enough as I turn the tuning dial.. the signal is there right where it should be on the center of the dial....
Ok.. so that means that EVERYTHING is in fact working.... yet I still can not get a signal off the air!
What gives here?
So I clipped another antenna lead to the grid of the 6sa7 RF stage... but I still got no signal... except a slight weak one with volume all the way up.. and that is a nearby 50kw station... how can this be??
So fiddling around measuring voltages on the RF stage .... and each time I touch pins, the leads make static sounds that are real loud... but the signal is still down in the mud!
just shot-gun fiddling...I clipped the external antenna right onto the oscillator coil and now I can get some stations... but way off frequency of course as I'm killing the oscillator.. but there is at least medium strength signals coming in now.
So I stopped and said... wait a minute I should be able to just use my brain and think this through... but just like Curly from the 3 stooges says.. " I'm trying to think... but nothing's happening"!!
This was now the craziest thing I ever had to deal with.
So while trying to think I started replacing a few wires here and there just to make sure I didn't have any internal breaks or cold joints... and nothing is making any difference.
I was drawing blanks. I had no clue what to do.
Then I look at the other trimmer for the oscillator right next to it and I notice that the screw head looks a little different.
I cut it shorter and the radio plays like a dream.
|Troubleshooting a screw?|
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