pin 1 goes high until the LED D4 forward
biases. This voltage starts rising and the
voltage at the feedback point pin 2 of the
XL4005 causes the switching regulator to
begin to shut down. The side benefit of
forward biasing D4 is that it begins to light
and shows that the switching regulator is
current limiting. The second comparator of
the LM358 uses a set point that is 1/10 of the
current limiter value established by R6. This
comparator is used when charging
rechargeable batteries. It indicates when the
rechargeable battery reaches a trickle current
by lighting the charge complete LED.
To solve the problem of
over-voltage to the +5V and
+3V regulators, we must
modify the CV/CI module;
refer to Figure 7. To do this,
we must first separate the
CV/CI module switching
regulator from the display
board. Carefully remove the
blue input terminal block
from the switching regulator board
shown in Figure 7 (A “1”). We must
then scrape off the red solder mask
shown in B “ 2” and cut the trace shown
in C “ 3.” Then, the scraped area from
step B “ 2” must be tinned as shown in
C “ 4.” It might be wise at this point to
use solder wick to remove any excess
solder. After reassembly of the module,
we will be soldering a red wire to this
The last step is to put the blue input
terminal block back on; be careful to
assemble it in the right direction.
Remove the two trim pots. I think the
best way to do this is to cut them apart
with a pair of dikes until the wires are
flush with the circuit board. If you try to
save the pots at this point, you may
damage the circuit board which is far
more valuable than the trim pots: see Figure 8.
Using solder wick, remove the charge complete LED,
the battery charging LED, and the constant current LED.
Now, connect a wirewrap wire to the plus and minus solder
pads of each of the three LEDs, along with the current pot
and the voltage pot. I like to use hot melt glue to prevent
the wires from breaking the pads off and to secure them to
the circuit board. Connect the two boards back together
with the standoffs. Solder a red wire to the + 7.2V input; this
will be connected later. Take a look at Figure 9.
For mounting the module, I took some insulated steel
floral wire as shown in Figures 10 and 11. I used five
minute epoxy to tack the wire down. Next, I prepared my
front panel. First, I printed the front panel artwork, then I
May 2014 29
; FIGURE 7. CV/CI module PCB modification.
; FIGURE 6. Switching
power supply module
32V input, 7.2V output.
; FIGURE 8. CV/CI module trim pot modification.