voltage by 0.3 to 0.4V, which has the effect of reducing the output power. D3 is shown on
the microcontroller section of the circuit diagram, see earlier.
If you are brave, and confident that you will NEVER connect power to the radio with
reversed polarity, you can omit this diode and fit a jumper wire over it.
The route of power through the switching and regulator circuits is as follows:
• Power enters the QCX-mini at the 2.1mm power connector on the rear panel.
• A 3-pin header pad connector could be fitted at JP26 to provide un-switched power
to additional boards; or if you wish to manage power switching in other ways, the thin
trace between pins 1 and 2 of this 3-pin header could be cut.
• D3 (1N5819) provides reverse polarity protection and can be omitted if you wish, just
bypass it with a jumper wire. You will gain some power output since the diode’s 0.3
or 0.4V loss will be removed. But your QCX-mini will have no protection against a
reverse power accident.
• A 2-pin header pad connector JP15 can also be used to provide polarity-protected,
un-switched power to another PCB above, or the trace between the pads could be
cut to provide switching control elsewhere.
• 2x5-pin connector JP3 now routes the 12V power to the front PCB
• A latching push-switch on the front panel acts as the On/Off switch for the QCX-mini
• The switched power now returns to the main QCX-mini PCB again via the 2x5-pin
connector JP3
• The switched +12V power is connected to the 7805 and the rest of the circuit. There
is also a 3-pin header JP27 which may be used to connect this switched power to
additional PCBs for modifications etc.
5. Fault-finding
Refer to :B$KEEI$EI>EI> and the groups.io discussion group for more tips!
5.1 Blank LCD or blocked LCD
If your LCD screen looks like either of these, then it is a sure sign that you have not
adjusted the contrast trimmer potentiometer R47.
101
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