I need an electrical schematic too, for this version. I see some modification on pcb, instead of LM334 i found two diodes, and instead of coil 22uH i found a resistor with 0 ohm value. All of those where covered with some epoxi.
https://i.postimg.cc/ZRsxQbbS/Se510cb3c6afe4f628b63ef59f1816bcct.webp
https://i.postimg.cc/502mpYMg/photo-2024-03-02-12-29-49.jpg
https://i.postimg.cc/rpJJSG7z/photo-2024-03-02-12-29-49-2.jpg
https://i.postimg.cc/ZRsxQbbS/Se510cb3c6afe4f628b63ef59f1816bcct.webp
https://i.postimg.cc/502mpYMg/photo-2024-03-02-12-29-49.jpg
https://i.postimg.cc/rpJJSG7z/photo-2024-03-02-12-29-49-2.jpg
Hello, I decided to buy a set of 606. I had collected a couple of 707 before, everything was fine. But 606 doesn't work as it should. The constant output voltage in one channel is 31 mV, in the other 190 mV. The frequency response is overwhelmed from 8 kHz. Huge noise and distortion.
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This is wrong. Where can I find the actual schematic for which this board is made? The board doesn't work and without a real circuit it's hard to fix it!
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I always check all the details before installation. But I decided to double-check with a multimeter that all resistors were installed correctly. And the 2M2 resistor showed a resistance of about 500K. The resistance leakage turned out to be due to the 1.0 uF capacitor. Perhaps I haven't found everything yet. I don't think all kits are like this. I bought two sets of QUAD 707 from different sellers and everything was fine. And the operational amplifier looked different from the ones I bought earlier and there was corrosion on the legs. I just replaced it with the Lm301 that I had.
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I don't think the 1UF capacitor is damaged. Because it is a CBB capacitor.
I think it's possible that the 25V33UF capacitor is damaged. It is an OSCON capacitor produced by Samwha capacitors in South Korea
But I once discovered a 25V33UF samwha OSCON capacitor with a short circuit. Replacing it with a 25V22 or 35V47UF ordinary electrolytic capacitor can solve the problem.
A diode is a constant current diode. Also known as a steady current diode. Place the circuit in a fixed current state of 1.5MA.
Can replace 2SJ503 and LM334. Diodes can also be omitted. The use of IC has the same effect as JFET.
So it cannot be replaced. Be careful to protect. So I applied glue to avoid collision damage.
Fourthly, I believe that the operational amplifier TL271 cannot be damaged. It is a genuine product produced by Texas Instruments.
It is recommended not to replace with LM301 or other operational amplifiers. Although operational amplifiers are universal. But the effect will vary.
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