I'm looking at this Pioner SX-737 which has distortion on one channel, the distortion starts after 20 minutes of playing.
The only other thing to mention is that this sandcast resistor becomes incredibly hot after only 2 to 3 minutes, so hot that I can't hold my finger on it.
Any ideas guys? Thank you!
The only other thing to mention is that this sandcast resistor becomes incredibly hot after only 2 to 3 minutes, so hot that I can't hold my finger on it.
Any ideas guys? Thank you!
If the caps are original, it's time for them to go. And replace that resistor.
jeff
Thanks for replying Jeff. I replaced the white sandcast resistor and the three caps and whilst doing this replaced all the transistors on the power amp board not pictured. Sadly that resistor is still becoming extremely hot.
Here's the parts I've replaced so far.
Replace the big cap and trace where the 180 ohm resistor goes and what voltage should be on it.
Did you replace the To 220 transistor and the to92 or both. Both should be done. If there is a zener there it should be tested.
Did you replace the To 220 transistor and the to92 or both. Both should be done. If there is a zener there it should be tested.
The hot resistor is not necessarily abnormal.
It may be normally dissipating enough power to reach such a temperature.
Measure the DC voltage across it to see.
It may be normally dissipating enough power to reach such a temperature.
Measure the DC voltage across it to see.
Is that resistor 180 ohms, or 180K ohms, cause on the schematic it's supposed to be 180 ohms.
jeff
And how would a 180k resistor get "incredibly hot"? At even 100V it would be well below 0.1W dissipation.
Exactly what I was thinking.
OK, I had a look at some used AWR-057 PS boards on ebay, and they all have the same "K" designator on that 180 ohm resistor, so please disregard my question.
jeff
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Interesting, and that's no exaggeration when I say after approximately 2 to 3 minutes from power on, the resistor gradually becomes so hot that I can't hold my finger on it for more than a second or two. You can see burn marks around those traces.
So next is to recap these? Or just the big 1000uf 50v cap? Many thanks to everyone replying and helping me learn!
Awr-057 is a power supply. To understand the function look at the schematic. The 180-ohm 5W resistor is there to reduce the voltage, share the load with the series pass regulating transistor attached to the heatsink.
It’s supposed to get hot, so you are assuming somethings wrong but in fact it’s supposed to be that way and is most likely not the cause of your issue esp if one channel works properly.
On Pioneer big schematics they usually state current drawn from each supply, so you can measure the voltage drop across the 180-ohm to calculate the current drawn.
It’s supposed to get hot, so you are assuming somethings wrong but in fact it’s supposed to be that way and is most likely not the cause of your issue esp if one channel works properly.
On Pioneer big schematics they usually state current drawn from each supply, so you can measure the voltage drop across the 180-ohm to calculate the current drawn.
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Sadly there is now no output on either channel upon power up today and that resistor is like tapping your finger very quickly on a clothes iron. Double checked pinout on the new amp transistors too.
Relay isn't kicking into action now.
Hope someone can help guide me as it's such a nice amp with a great warm tone.
Thanks in advance guys!