Radoslav Borisov borissov

After encountering error E9 (a problem with the locking mechanism) on my Beko washing machine, I replaced the locking mechanism, but the error persisted. Upon further investigation, I concluded that the issue was with the main control board. After removing the board and conducting a visual inspection, I discovered charred components. I ordered a new T2 transistor and new R21 and R50 resistors. After replacing the locking mechanism and the components on the board, the machine is working like new again.

![Added new T2 transistor and new R21 and R50](https://gist.github.com/user-attachments/assets/21794909-9d09-4062-b171-f

After prolonged use and numerous issues with the Keychron K8 in Bluetooth mode, I concluded that the problem was entirely hardware-related after exhausting all possible software solutions.

Upon opening the keyboard, I noticed that the Bluetooth module was placed in a highly unsuitable location—sandwiched between the aluminum case on top and the battery underneath. This positioning severely impacted signal strength, leading to frequent connection drops and input issues.

To improve connectivity, I decided to relocate the antenna by extending it using a blue wire from a Cat6 Ethernet cable, which was the best option available at the time. While the wire’s dimensions and properties might not be ideal, a Wi-Fi antenna from an old laptop or router would likely be a better choice.

The PP500 phono preamplifier, built around the JRC4580 op-amp, originally uses 3.3 kΩ resistors and 4.7 µF capacitors in the feedback network. While this design is stable, it can result in a lower output level when used with medium-output MM cartridges such as the Audio-Technica AT3600L.

To increase the gain and improve the low-frequency response, a parallel RC modification was applied. In this case, a 1.5 kΩ resistor in parallel with the original 3.3 kΩ resistor, combined with a 10 µF capacitor in series, was added. This effectively adjusts the feedback loop, increasing the overall gain while maintaining the low-frequency cutoff around 10 Hz, ensuring

Optimizing Gain and Power Supply Noise

The PP500 phono preamplifier, built around the JRC4580 op-amp, originally uses 3.3 kΩ resistors and 4.7 µF capacitors in the feedback network. While this design is stable, it can result in a lower output level when used with medium-output MM cartridges such as the Audio-Technica AT3600L, and the stock power section is highly susceptible to interference.

To optimize both the gain and power filtration, a comprehensive modification was applied. In the feedback network, after iterative testing with different values (1 kΩ, 2 kΩ, and 2.5 kΩ), a 4.7 kΩ resistor in parallel was selected as the perfect sweet spot—balancing high clarity with the necessary volume output. This was combined with an upgraded 10 µF capacitor to optimize the low-frequency response and ensure proper RIAA correction.

Significant improvements were also made to the power supply stage to eliminate noise. The stock 1000 µF filtering capacitor was replaced with a much larger 2200 µF unit, byp

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