Silicon Chip – July 2019

siliconchip.com.au Australia’s electronics magazine July 2019 87

Fit a fuse with a rating as recom-
mended for the transformer you are
using. This may be around 1A, or pos-
sibly slightly more if using a toroidal
transformer, as these can have a high-
er inrush current when power is first
applied.
During the following testing steps,
if using a mains power supply, ensure
that you can’t come into contact with
any of the mains conductors while
probing the board.
Set your multimeter to a low DC
volts range (eg, 20V). Before apply-
ing power, check the markings on the
board to see where you will be prob-
ing. The right-hand end of the 0Ω re-
sistor/wire link below D26 is a con-
venient place to connect your black
ground probe.
You will be checking the voltages at
the +9V, -9V, +5V, +3.3V, and VA (5V)
pads, as indicated in Fig.11 on page 83
last month, and the PCB itself. These
voltages can vary slightly from those
indicated.
The acceptable ranges are: 9.2-10.4V
(±9V), 4.7-5.4V (+5V, VA) and 3.15-
3.6V (+3.3V).

There is no visible indication when

the power supply board is powered up.

As soon as you have applied power,

check the DC voltages at each of the

above points.

If any of these are wildly off, check

the AC voltage(s) being applied to

CON13 and ensure that they are not

too far from the nominal 12V. The

transformer being lightly loaded at

this time, readings of 13-14V would

not be surprising.

Note that because of the resistor val-

ues used to set the regulator output

voltages, and since there is no current

being drawn from the power supply

as yet, it is possible that the regulat-

ed rails may be even higher than the

ranges above suggest.

That’s because the worst-case mini-

mum load requirements of the regula-

tors are not catered for with the other

boards unplugged.

So if any of the expected readings

are below the ranges specified, or well

above them, then you should switch

off and check for faults.

But if they are slightly too high, you

can try connecting a 100Ω resistor from

Fig.16(a): how to connect a

PICkit to program the CPU

using hook-up wire or patch

cables. Note that the PICkit is upside-

down so that pin 1 is at the bottom.

Keep the wires short, or programming

may fail.

GN

D

CON1 0 COCONN

CON9

SP

I2/I

2 S

1

1

100nF

100nF

100nF

ICSP

CO

N2

3

1

1

REG3

POPORTRTBB

JP 5

1.2kW

390 W

D1 5

10kW

1kW

8

7

6

(PGEC) 5

(PGED) 4

(GND) 3

(VDD) 2

(MCLR) 1

BACK

OF

PICKIT 4

8

7

6

(PGEC) 5

(PGED) 4

(GND) 3

(VDD) 2

(MCLR) 1

BACK

OF

PICKIT 4

Fig.16(b): alternatively,

you can use an IDC header

on a short 10-way ribbon

cable soldered to a pin

header for programming.

Fig.17: the first

step to set up

MPLAB X IPE

is to select the

correct PIC chip,

as shown here,

and check that it

has detected your

programmer.

the test point to ground to see if that

brings the reading back down into the

expected range. If it does, then you

can proceed.

Otherwise, start looking for solder-

ing or component faults.

Programming the micro

Once you’re confident that the pow-

er supply is working, if your micro

is not already programmed, now is

a good time to do that. If you have a

An alternative to

mounting the unit in the plastic

case, as seen opposite, is to use a 19-inch

rack mounting case – here seen with a brushed

aluminium front panel for a really professional appearance.

Programming
with a PICKIT 4
is much faster
than with a
PICKIT 3,
which is
especially
helpful in
this project,
as the HEX
file is rather
large – 2MB.