sony st-242s tuner

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Carlosraj

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Joined 2010
Hi,

I have an old sony st-242 tuner. It has been working well all this while, but lately it has developed some problem. When I switch it ON and tune to any FM radio station, it works well for about 5 minutes. The sound then slowly fades off, the radio station is no more there, there is only some intimitent poping sound. The FM stereo indicator LED goes off. What can cause this. Thanks

Carlos
 
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Carlosraj

Member
Joined 2010
Max Headroom said:
You could try just the resoldereing and see what you get.
While you are at it, inspect the whole board(s) for crook solder joints.

Let me know what result you get.

Dan.
Click to expand...

Great!, it really worked. I did not replace any component but resoldered the whole board. After resoldered, I tuned into a FM station and left it on for more then 2 hrs, and it works perfect. Thanks alot again Dan

Carlos
 
sgrossklass

sgrossklass

Member
Joined 2004
stephan.win31.de
Max Headroom said:
Congratulations on your first repair....now to mod/improve it, lol.
Click to expand...
Doesn't look that tweakable tbh. The frontend is a pretty decent little 3-ganger but I see no easy way of adding RF/IF AGC. The IF filter is one of those old 4-pin jobs. The matching version of Bill Ammons' Filter Adder PCB could be used there, maybe with two 180 kHz Muratas for a start. Should give a nice boost in selectivity.

Small-fry electrolytics around the stereo decoder (C217-C227) should be looked at; low-leakage types (orange ELNAs) are likely to be OK still, others may warrant replacement. C220/221 are a bit on the small side to begin with. Besides, I'm not sure why they did deemphasis like that. Probably to get output level up. Looks like it could use a buffer. No pilot tone filtering at all, not even to the extent shown in the LA3361 datasheet - meh. Very basic, that tuna.
 
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