Hi, I've received excellent help here before regarding replacing caps and transistors on vintage gear and would appreciate some more. I have a Technics by Panasonic SA-500 receiver that when switched to phono makes a constant, rapid popping sound that goes away when volume is turned down and increases when volume is turned up. I assume the capacitors and maybe transistors need to be replaced on the phono circuit board. Can anyone tell me which ones and good replacements for them? Found a tech schematic on hifiengine. Just need to know which components I need to replace and where to get them.
Thanks.
Thanks.
Is this on one or both channels?
The phono stage is opamp based and so unlikely these would be at fault.
Edit... if on both then check the PSU first. Check the voltages. C705 can be bridged with another as a test.
The phono stage is opamp based and so unlikely these would be at fault.
Edit... if on both then check the PSU first. Check the voltages. C705 can be bridged with another as a test.
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Put your meter on DC volts and use the chassis as ground. Carefully measure the voltage on each end of R703 for starters (in the diagram above). The voltage should be constant and approx as marked.
That's a start but its not conclusive because the meter can not show noise or ripple.
That's a start but its not conclusive because the meter can not show noise or ripple.
Ok. I will do that next week as I am off. What would be next...if the voltage is okay...
If I need new transistors do you recommend a site?
If I need new transistors do you recommend a site?
Take it one step at a time. Ideally we should do more detailed tests looking at the supply with an oscilloscope... without that its all more guesswork. If the voltages are incorrect we have something to work to. If they read OK we are guessing.
You should check the 1k resistor is OK by lifting one end of it to measure its resistance. Do the same for the 39k (it says 39k but could be 3.9k the way the typing is spaced) The 2.2 ohm is low enough to measure in circuit.
The transistor can be shorted out as a test. You can link all three pins to each other. The circuit should work normally beyond having a bit more ripple on the supply.
C705 can only be checked by replacement (or tagging a new one across the old one) That is a likely suspect.
Where you live depends on where you get parts but all these are common generic items replaceable with common off the shelf replacements. I would advise buying off eBay as to many fakes and poor products around.
Do the measurements, see where that gets you.
You should check the 1k resistor is OK by lifting one end of it to measure its resistance. Do the same for the 39k (it says 39k but could be 3.9k the way the typing is spaced) The 2.2 ohm is low enough to measure in circuit.
The transistor can be shorted out as a test. You can link all three pins to each other. The circuit should work normally beyond having a bit more ripple on the supply.
C705 can only be checked by replacement (or tagging a new one across the old one) That is a likely suspect.
Where you live depends on where you get parts but all these are common generic items replaceable with common off the shelf replacements. I would advise buying off eBay as to many fakes and poor products around.
Do the measurements, see where that gets you.
