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This is only a preview of the February 1997 issue of Silicon Chip. You can view 25 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "Computer Controlled Dual Power Supply; Pt.2":
Items relevant to "Control Panel For Multiple Smoke Alarms; Pt.2":
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one of the output power transistors,
an NEC D587.
Unfortunately, this has stumped
the locals, who don’t require a lot of
stumping, if I may say so. If you can
help me in sourcing a supplier I would
be most grateful. The only reason the
speakers go is because my other half
is getting hard of hearing. A hearing
aid would be cheaper but this is a
no-go area. Hope you can help. (H. F.,
Perth, WA).
• We suggest that you consider in
stalling PTC polyswitch thermistors
in series with the speakers. These
go temporarily open circuit if their
current rating is exceeded. We suggest
you try installing a type RXE090 or
RXE110 PTC thermistor. These are
available from Jaycar Electronics in
Perth. Phone (09) 328 8252.
As far as the output transistors are
concerned, why not contact your local
Mitsubishi service agent? They are at
329 Collyer Road, Bassandean WA
6054. Phone (09) 377 3400.
Troubleshooting the
Insulation Tester
The Insulation Tester described in
the May 1996 issue of SILICON CHIP
is a very useful piece of equipment
but I have found that the voltages
produced are somewhat lower than
expected. The 100V, 250V and 500V
ranges all produce about 150V. The
600V and 1000V ranges both produce
about 450V.
This is an improvement upon the
19V, 148V, 465V, 540V and 290V being
produced from the respective (lowest
to highest) voltage ranges after first
completing the project but still not
optimal. I effected this improvement
by replacing the CMOS oscillator
chip as I had noticed that the CRO
traces from the oscillator when the
100V range was selected were almost
nonexistent. Could the replacement IC
be faulty as well or is there a problem
with the error amplifier?
Keep those great projects coming.
(N. P., Seven Hills, NSW).
• Your problem is possibly due to
incorrect transformer windings. Check
that the secondary is wound in the
same direction as the primary wind
ing as shown in the diagram of Fig.4
(page 35, May 1996). Try winding the
secondary in the opposite direction to
the way it was.
In addition, check that the range
Dud micro in
Dolby decoder
I have recently purchased the
Dolby Pro-Logic Surround De
coder, Mk 2, as described in the
November & December 1995 issues.
My problem is that, upon powering
up the unit, the display does not
flash “—” at all and the relays do
not change state. In addition, the
noise LED does not light when the
noise sequencer button is pressed.
I have measured the voltages on
the power supply module and all
are ±5%. I have also measured the
voltages on ICs 1-9 as indicated on
page 78 of your magazine article
(bearing in mind the errata previ
ously advertised).
I have identified that when the
unit is powered up, the measured
voltage at PC0 is 0V and remains
at 0V; ie, it does not go high. Hence
Q1 does not switch on to energise
the relays. I have removed IC6 and
applied 5V to each of the 7-segment
LEDs and ascertained that the
7-segment displays are not burnt
out but are in good working order.
resistors on switch S2b are arranged
on your PC board in the correct order.
Flatpack transistor
washers
I am looking to use the new flatpack
MJL21194/21193 tran
sistors as fea
tured in the April 1996 issue but am
having trouble finding the isolating
mica/silicon washers. The magazine
article shows a washer bigger all round
than the transistor. Where did you get
yours? (R. G., Chapel Hill, Qld).
• You can obtain these washers from
Altronics in Perth. They have two
types: silicone/fibreglass Cat. H-7220
x 4 or mica type Cat. H-7120 x 4. You
can phone Altronics on 1 800 999 007.
Trigger happy laser
pistol user
I am writing in regards to the laser
pistol and electronic target described
in the December 1996 issue of SILI
CON CHIP. Could you please suggest
a way to alter the circuit so that the
Each of the switches S5, S6 and
S7 produce 5V at pins 17, 18 and
19 of IC6 respectively when not
pressed and 0V at the same pins
when the respective switches are
pressed. Pin 2 of IC6 remains at 5V
all the time.
I have noted that the voltage sig
nals for “B, A, E, R, S, D” are 5.4V,
1.0V, 2V, 2V, 2V respectively and
that they do not change under any
condition. I have noticed, though,
that IC6 was supplied as an MC
68HC705C8ACP, not an MC68HC
705C8P. I assume that this is just
another variation of the MC68HC
705C8P microprocessor chip and
is a valid substitute. Could you
please help me identify what is
the problem with this kit? (C. C.,
Leeming, WA).
• It appears that the microproces
sor (IC6) is either not programmed
or faulty. If it is programmed it
will be marked accordingly. Either
way, the microprocessor should
be replaced. The ACP version is
slightly different to the P version
but we have programmed them to
accommodate this difference.
laser will remain on constantly when
ever the trigger is pressed down? It
occurred to me to short the 1.5kΩ
resistor but I figured this would still
create a pulse because of the 100µF
capacitor. Your help in this matter
would be much appreciated. (J. N.,
Greenacre, NSW).
• As you suggest, shorting the 1.5kΩ
resistor will allow the laser to stay on
while ever the trigger is pulled. The
100µF capacitor can then be omitted.
Notes & Errata
MultiMedia Loudspeakers, November
1996: the perspective diagram on page
61 shows the wrong enclosure depth;
it should be 224mm.
Control Panel For Multiple Smoke
Alarms, December 1996: a 47kΩ re
sistor should be added to the circuit
between pin 11 of IC5f and the +9V
rail, while one of the 100µF bypass
capacitors on the +9V rail should
be 10µF. Note also that the parts list
should show four 1kΩ resistors (not
SC
three).
February 1997 93
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