This only applies to first batch test units. Second batch public D7 units have a factory correction that eliminates this modification.
Bypassing the Controller LCD Power Boost Circuit
There have been reported instances of burning / smoke coming from the D7 controller board (in beta testing) and has been found that the controller board has a boost power regulator circuit that is not required (from a different model?). This can cause a clicking sound in the D7 and isn’t required because the UV LED is using an off-board LED driver power module.
Some quick notes and a potential mod on the electronics or even just the wiring. The stock LCD Printer Board V1.0 has an onboard current limiting regulator meant to directly drive a large LED such as the UV light source and current limit it. The issue there is that many diode arrays such as the one used are strings of series LEDS and requires a higher input voltage than 12V. This is why the mini brick style LED driver module is in between the control board and the actual LED array. So the note was that my particular machine was making a noticeable “clicking” sound that was coming from the inductor on the control board. After doing analysis and reverse engineering of the board and routing, I also grabbed this data sheet on the onboard current limiting driver IC http://www.ti.com/lit/ds/symlink/lm3429-q1.pdf.
The point is, we do not need redundant regulation and in fact, it causes a bunch of issues, one of them being this clicking pulse that cannot be good for the electronics long term. So what I also discovered is that the FET is controlling the ground return path. So the current limiter appears to control the +12V LED output and the FET controls the return to ground. There is a second 12V controlled output and on that, the 12V + terminal is directly connected to the 12V input. So the trick is 2 things. First simply move the + input wire of the LED driver module to the other 12V+ screw terminal on the control board. That limits the entire current limiting section we don’t use anyway. However, that does not stop the “ticking” sound. The quick fix on that is to disable the LED current limter be desoldering the inductor. This then allows a nice smooth PWM transition of brightness and control over the UV LED. Pretty cool change and could save Wanhao some money if they just build the board sans the components.