Sadly not the best of good lookers but one of the 'all time greats' in portable radios came my way almost as a gift the other day (the price was right). Much smaller than early German Sat's, so less bass'y, but that comes with the advantage of lightness and extended battery life, that's thanks mainly to modern integrated computer circuits. It does have a 12 volt plug power socket on the side, another weight saver (no internal transformer.) The back screws were in a polythene bag at the rear when I collected it (always a bad sign). I turned it on and to my surprise it all worked fine, the doorbell rang and I went and answered it (the postman) and when I returned the audio had gone 'tits-up', turned into white noise, oh dear.....
The repair
Now before I start on a new project I always find a nice PDF of the full service manual and have a quick look through, then I check technical chat rooms on the net encase anybody else has spent hours of their life repairing the same fault, and low and behold my good idea came to fruition. A few people had experienced this fault over the years, in varying symptoms similar to mine, and the best suggestion was to replace
C138 a
10-30pF pre-set capacitor as shown in my diagram:-
Modern radio circuits can cover an area of a football pitch, so I've blown-up the area in question, the pot itself is contained in a metal screening box with a hole to adjust it, a little tricky to remove, so before doing that I thought I'd try adjusting the control before stripping everything down. As soon as I adjust the control the set sprung back to life! But when I tried it again a few hours later it was still dying after 5 minutes of operation. So I thought let's mark the screening can with a felt pen and try different values of adjustment until I find the one that works for this set. (looks like the control shapes the xtal derived oscillation waveform)
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| If you need to change the pot un-solder the 3 tuning control wires and remove inner chassis screws, the print will all open out nicely |
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The capacitor in question is easily found center bottom of the metal can as shown in the manual scan below. (diagram about life size) Don't forget to keep all screws in a pot so you don't loose them, I use the lid off an aerosol can. Whenever youre repairing stuff make sure the bench has a rubber coating and is kept clean, it's so easy to scratch modern painted radios while repairing them.
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| Aluminium screening can layout from manual |
After only 2 guess adjustments of the control the radio seams to work fine and as so now for over a week, if anything more develops I'll let you know.
Permanent storing of up-to 42 stations and their names can be programmed into the EPROM, that doesn't need battery's to hold in memory.The tuning of this radio is done by pressing button 'a' in my diagram followed by 4 digits and decimal point if needed and then press 'a' (red arrow) to store at end. Make sure you have selected the correct band also. The tuned frequency can be given a 4 digit name by pressing button 'a-z', select character with tune control and move to to digit by pressing 'a-z' again. Simples, lol
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