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RX 5050 - Anyone have a schematic?

panasonic rx 5050 schematic rx5050 circuit repair

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#31 chuckulaa

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Posted 30 June 2017 - 12:14 PM

@caution sent me a potentiometer that I got in yesterday! To install it, I kept the shaft and contacts of the original pot, and the mounting bracket. I just replaced the wafer with the carbon tracks on it. I had to bend the legs to make it straight, and jumper 'pin 1.' I made the jumper with a resistor leg. Took me about 10 minutes, and the radio is now working!

 

One weird thing I noticed, capacitor 129 and 229 were different values? One was 0.33uf and the other was 0.22uf. I replaced both with two 0.22uf capacitors. I will be interested to see the schematic so that I can know what value was intended for these positions.

 

I went ahead and replaced several capacitors with replacements that I have on hand. The radio is now working, but it has a large background hiss, so I'm going to rebuild the power supply as well. I plan to purchase a schematic so that I can replace Q303 (the rusty transistor), replace the diodes from the diode bridge, and replace all of the remaining power supply capacitors. I hope that this will not only remove the hiss, but it will make this radio last a long time.

 

The RX-5050 sounds alright. It doesn't sound near as good as my '69 pioneer receiver combined with my mid 70s rectilinear speakers, but it sounds pretty decent good. It is very loud, and it is quite a bit brighter. I have found that EQing it by boosting the bass and flat lining the treble gives the best tone. If and when I purchase a schematic, I will post it to this thread, so that someone else won't have to pay for the schematic in the future! 



#32 chuckulaa

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Posted 30 June 2017 - 08:56 PM

 

 

The transistor is an 8.5v voltage regulator and not likely a problem because if it had failed, you would notice much more problems than you are observing and it would be global and not channel specific problem.  

 

 

 

 

Superduper, would you feel comfortable suggesting a modern replacement? I want to rebuild the power supply.

 

Thanks for all your help, I've been enjoying this boombox all night tonight.

 

 



#33 caution

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Posted 30 June 2017 - 10:43 PM

Glad to hear the pot worked out! Sort of weird seeing someone put a good pot BACK INTO a 5050 :lol:

Not to steal SuperDuper's thunder but I may have an exact replacement for that transistor, what's its number?



By the way, great choice of receiver. I started my musical odyssey on a Pioneer SX-6000 (1971-73) that my father shoehorned into an old Montgomery Ward Airline 2955.



#34 Superduper

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Posted 01 July 2017 - 12:26 AM

The transistor is 2SC1568.  Virtually any TO-126 NPN power transistor will work, recommended 1.0 amp or greater collector current.  The application for which this transistor functions is not critical.  However, when subbing, always compare the datasheets for the orig as well as the substitute to verify pin out assignments are the same, or adjust accordingly.  In most cases, if the assignment is different, it can usually be corrected by reorienting the device 180 degrees as the center pin is "usually" the same.  However as I mentioned earlier, why are you selectively replacing components indiscriminately without knowing for sure if there are problems?  It's easy enough to check...  with unit running, check voltage at B/C/E.  If you are getting approximately 9.2/12/8.5, then the transistor is doing it's job perfectly and there's nothing wrong with it.  The rusty part is NOT the transistor -- it is merely a heatsink that is clipped to it.  If you change the transistor, the heatsink will need to be migrated over and it will still appear rusty.  So if the appearance bothers you, then simply remove the heatsink, wire brush it, repaint and replace.

 

BTW, the original caps that you replaced were the correct value.  It is unclear why the engineers set the values differently but it could be due to the fact that the two outputs have slightly different potentials, slight as it is (5.6 vs. 5.7).  Besides, they are polyester caps -- they typically don't go bad like electrolytics.  

 

As I mentioned in another thread, the power supply is not usually a source of hiss.  PS introduced noise typically manifests as hum since it is 60hz related.  Hiss on the other hand is random noise and not of any set frequency.  If you want to know for sure, simply power it on batteries and if the hiss is still there, then you'll know that the PS is not the source of the problem.  I'm not against rebuilding the power supply.  If nothing else, new caps may help stiffen the PS and certainly can be considered preventative maintenance to ensure future issues don't rear it's ugly head.  New rectifier diodes?  Well, I suppose they are cheap enough but again, throwing parts...  why not replace all the semiconductors then?  I mean, what's the rationale for replacing these?  Anyhow, that's just me -- I like to take a logical approach towards repair.



#35 chuckulaa

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Posted 01 July 2017 - 10:23 AM

Cation, I love the pioneer SX receivers. I have a SX-1000td.

 

Because I ended up getting the RX-5050 for free, I figured it wouldn't hurt if I invested a little in it. Superduper, you build a strong case. I can't argue with a practical, logical approach. I may replace the remaining PS capacitors for preventative maintenance, but I won't pursue replacing the semiconductors.

 

I'm excited to have this RX-5050. The sound is a bit tinny and thin, but the box does have enough articulation that I can hear all the tracks in a recording. Another bonus: because it is not super valuable, or rare, it will make a nice camping/beach boombox. If it gets a little banged up its not a big deal!

 

Thanks again guys, I really appreciate it.





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