Fan regulator
This simple mod, originally described by tinhead on EEVBlog forum, is intended to make built-in cooing fan quieter. Typical problem with cooling fans is the noise they make and typical solution is to decrease voltage (and therefore current) to the fan to make it rotate slower. Hantek DSO5000-series oscilloscopes have 3 terminal 12V regulator dedicated for the fan (pointed at by an arrow on the title picture). To change the fan voltage I simply need to replace the regulator marked U7 on the power supply PCB.
Tinhead’s original mod was to replace 7812 (12V) regulator with 7805 (5V). It will work assuming good quality fan. Mine refused to start from 5V so I used MC7808 – a 8V regulator. Another good candidates were 7806 and 7809 but after first try I decided 8V is good enough – the fan is spinning well and the noise level is low.
The following picture shows power supply PCB unscrewed from the chassis and turned upside down. Again, an arrow shows the regulator. The PCB is single layer; replacing the regulator is a simple matter of removing solder with a solder wick, pulling the original regulator out and soldering on the replacement. If everything is at hand, the mod takes about 15 minutes to complete, including testing.
Enjoy!
Oleg.
Bottom side of the PCB