I repaired a crappy little boombox

rulerboyz

AK Member
I came across a Sony CFS-920 that only had sound coming from one speaker. Just for the sake of practice I decided to see if I could get the other speaker working. I first tried to determine if it was a bad speaker, but both speakers were fine. I then tested the transistors, diodes, resistors (there aren't that many in the amp section). I put new caps in the amp section (panasonic ones I got from a computer power supply). I figured it must be a bad IC so I ordered a new one (for a few dollars) it has 12 pins.

Soldering on these cheap flimsy boards can be tricky because the traces lift very easily. I had to connect all 12 of the leads with wire to the next solder joint in the path. I had replaced two transistors and that was also a challenge because I had to connect the base, collector and emitter with wires again. It took a little bit of fiddling to get the solder joints on all 12 pins in good enough shape to get sound from both speakers. I was quite satisfied with the result as far as the FM radio sound goes.
 
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You very well articulate the satisfaction of tackling a job no one would do, doing it well, and getting a great result.

:thmbsp:


rulerboyz said:
I came across a Sony CFS-920 that only had sound coming from one speaker. Just for the sake of practice I decided to see if I could get the other speaker working. I first tried to determine if it was a bad speaker, but both speakers were fine. I then tested the transistors, diodes, resistors (there aren't that many in the amp section). I put new caps in the amp section (panasonic ones I got from a computer power supply). I figured it must be a bad IC so I ordered a new one (for a few dollars) it has 12 pins.

Soldering on these cheap flimsy boards can be tricky because the traces lift very easily. I had to connect all 12 of the leads with wire to the next solder joint in the path. I had replaced two transistors and that was also a challenge because I had to connect the base, collector and emitter with wires again. It took a little bit of fiddling to get the solder joints on all 12 pins in good enough shape to get sound from both speakers. I was quite satisfied with the result as far as the FM radio sound goes.
 
I put a few new caps in the preamp section too to see if I could bring a little life to the dull sounding tape player. It worked however I must have introduced a lose connection because the tape mode is now picking up some radio interference. I imagine not that big a deal to fix, however dismantling the unit is probably the most tedious part of the repair job.
 
You fixed it the way I would. I wish I was smarter and could determine which component was bad and fix only that one. To do it our way on a big receiver is not very practical.

Finding the defective electronic part has been my biggest frustration in messing with electronics.

Sometimes one gets lucky and finds a bad solder joint or a broken wire but not often.
I did that on a SX-780 but had hints where to look from the internet but that was rare. I have a couple receivers with one good channel and even swapped power transitors but still bad.

Charlie
 
It really takes a lot of perseverance and good observations skills sometimes to find the problem (when you don't have a lot of diagnosis tools at your disposal), and sometimes it still eludes you.
 
This is a very satisfying thread. Who says a crappy little boombox isn't worth the effort? In another twenty years there will be whole websites devoted to the cult following of "vintage" crappy little boomboxes populated with odd fellows who have nothing better to do with their time than re-animate thriftshop and yardsale "scores" while their sensible and decent wives wring their hands and cast their eyes heavenward wondering aloud, "Why?". I, for one, will look forward to the specialty forum "Everything Emerson".
 
Sadly, I eventually ran into problems with the boombox when I tried to recap the cassette/preamp section. I now hear radio interference when I play a cassette, and the am/fm is just giving me FM sounding static. The problem was intermittent at first then got worse. Looking more closely at the entire circuit board I realized that there were quite a few areas that were badly corroded (especially in the radio section which I had not looked at initially). The radio has spent all it's time outside exposed to all kinds of weather, so not surprising that there are some problems with the traces. Well at least for a bried time it sounded great. Perhaps on a better healthier boombox I will try again.
 
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