This simple modification, originally described by tinhead on the EEVBlog forum, is intended to make the built-in cooling fan quieter. A common issue with cooling fans is the noise they produce, and a typical solution is to reduce the voltage (and therefore the current) supplied to the fan, causing it to spin more slowly. The Hantek DSO5000-series oscilloscopes feature a three-terminal 12V voltage regulator dedicated to the fan (indicated by an arrow in the title image). To adjust the fan voltage, I simply need to replace the regulator labeled U7 on the power supply PCB.

Tinhead’s original modification involved replacing the 7812 (12V) regulator with a 7805 (5V) regulator. This can work, assuming the fan is of good quality. However, my fan refused to start at 5V, so I used an MC7808 — an 8V regulator. Other suitable options included the 7806 and 7809, but after the first test, I decided that 8V was sufficient: the fan spins reliably, and the noise level is low.

The following image shows the power supply PCB unscrewed from the chassis and flipped upside down. Once again, an arrow indicates the regulator. The PCB is single-layer, so replacing the regulator is straightforward: simply remove the solder with a solder wick, pull out the original regulator, and solder in the replacement. If all the tools and parts are ready, the entire modification takes about 15 minutes, including testing.