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How to unpack SMDs
without losing them
Thanks for a terrific challenge
with the SMD Trainer Board project
(December 2021; siliconchip.com.au/
Article/15127). I am looking forward
to getting to the smallest part that I
can manage.
One thing missing from all the
descriptions is how do you get the
little blighters out of their capsules
(cocoons, packaging, enclosures) without them escaping? I have struggled
with this problem more than anything
else so far, and am only on the large
components above the line.
This could be a good competition
for us old coots – the oldest person to
get the smallest component working.
I am 82. (D. L., Clare, SA)
● We usually hold the strips
component-
s ide-up and peel the
plastic cover off from the side using
tweezers. Peel it back to expose just
the number of components you want,
then turn it upside-down just above
your workbench surface, and they
should drop straight down onto it. It
helps to have a uniformly coloured,
flat mat (or even a sheet of paper) to
empty them onto so you can easily see
where they land.
You usually have to flip them over
after tipping them out, but there isn’t
much you can do about that.
We would be interested to hear
about the smallest parts that you
can manage. There are three of us
here in our early-to-mid 40s, and we
struggle with anything smaller than
M1206/0402. Even they are a bit challenging. We find M1608/0603 easy
enough, and anything larger than that
is a relative doddle.
USB Cable Tester
problem solved
I recently put together the USB
Cable Tester (November & December
2021; siliconchip.com.au/Series/374).
It all went together quite easily and the
calibration worked well.
108
Silicon Chip
But when I put it together finally
with the batteries inserted, it would
not go to sleep. For the LCD screen to
be initialised correctly, I had to wire
an external power switch to switch it
on with the box closed, after the LCD
had plugged into its socket.
With this switch connected, the LCD
was initialised correctly and showed
the countdown screen, but after the
countdown finished, I did not get the
main idle screen as shown in Screen 7
on page 92 of the December 2021 issue.
Instead, I get the following display:
USB Cable Tester
DFP: VBUS,SHLD,
When I insert a cable, the device
appears to work correctly. For example, with a Type A to Type B cable
inserted, I get:
CABLE INSERTED:OK
USB 2.0 0+ 0Check DFP and UFP.
327mV at 1A: 326mW
This tallies with Screen 8. If I then
press S1, nothing happens, so S1
doesn’t seem to act the way it should.
The device remains on and doesn’t
go to sleep. I hope someone can point
out where my mistake could be. (J. H.,
Nathan, Qld)
● We think you have a short circuit
between the Vbus pin and the shield
of one of the USB sockets (hence the
“DFP: VBUS,SHLD” message with no
cable inserted). Check the resistance
between those pins with an ohmmeter and inspect the sockets for solder
bridges.
Note: J. H. sent us a reply which
stated: your diagnosis was spot on.
There was a short between Vbus and
shield, but you would never guess
what caused it! After completing the
calibration tests, I inserted the jumpers JP1 and JP2 back on one of their
respective pins only.
Unfortunately, with the jumper for
JP1 sideways, the underside of the
jumper came in contact with the shield
of the neighbouring USB-C socket.
Even more unfortunately, there was a
little bit of the jumper’s internal metal
connector protruding from the base,
Australia's electronics magazine
which was enough to cause the short
between Vbus and shield. After fixing
that, the device works perfectly.
I’m so happy it wasn’t my soldering
that was at fault, as I would have to
go back to soldering 101 and repeat
the course.
Replacing USB Cable
Tester sockets
I have bitten off more than I could
chew by tackling the USB Cable Tester
kit (siliconchip.com.au/Series/374)!
I successfully soldered CON5 (Mini
USB). I then attached CON8, but in
testing it, it detached, pulling one of
the tracks off the board. So I really
need to start again.
I see that I can buy a replacement
board, but where do I get CON5 and
CON8 in the USA? Can you supply
these three parts so I can start again?
I’m not sure if I can use CON8 in practice because I don’t think it will ever
be strong enough to stand having a
connector inserted. The alternative
is to proceed without CON8. Will the
Tester function without it? (R. T., New
York, USA)
● You can certainly leave off any sockets, and the circuit will still function
otherwise (naturally not being able to
test that cable type).
We have all our micro-USB sockets (CON8) tied up in kits, but the
specified part, Würth Elektronik
692622030100, is currently in stock
at both Digi-Key and Mouser. As they
are both based in the USA, you should
have no trouble ordering from them.
CON5 is a very common type of connector made by many manufacturers.
You can use EDAC Inc. 690-005-299043 which is inexpensive and also
in stock at both Mouser & Digi-Key
(search for the part numbers).
We think the problem you had with
CON8 coming off the board and tearing tracks might be that you didn’t
manage to wet the mounting tabs on
either side properly with solder. Next
time, you could try adding flux paste
to both those tabs and the matching
siliconchip.com.au
pads on the PCB and make sure you
get the solder nice and hot so that it
fully adheres to both.
Not all software
includes ASM files
I built the SMD Test Tweezers kit
(October 2021; siliconchip.com.au/
Article/15057), but it does not work. I
need to find a data sheet for the OLED,
as I don’t yet know if the fault is in the
OLED or the PIC.
Also, I tried to download the .asm
file from your shop. I found the .hex
file but could not find the .asm file. (L.
C., Forest Hill, Vic)
● The OLED modules are based on
the SH1106 controller IC, although
we have seen some very similar modules with an SSD1306 controller. Both
data sheets can be found using web
searches.
The microcontroller code for this
project is written in the C language,
so there is no .asm file. Assembly language files usually are only used when
the micro is programmed in assembly language (which we are doing
less these days as it is more work and
harder to debug). The MPLAB X project, including the C source code for
this project, can be downloaded from
siliconchip.com.au/Shop/6/5948
Troubleshooting AM/
FM/SW Digital Radio
I have built the AM/FM/SW Digital Radio (July 2021; siliconchip.
com.au/Article/14926). When I power
the radio, all I get is a blank LCD (it
does light up). I built it using a pre-
programmed micro. What is likely to
be the problem? I tried pressing the
Reset button but that did not help. (R.
B., Burlington, NC, USA)
● It could be any number of problems.
Have you checked the voltages at critical points, such as the supply rails?
Do you get anything at all when you
adjust the contrast potentiometer on
the LCD screen? If LCD is not set up
due to program fault or wrong connection, usually just a line of squares
will appear.
SMD soldering can be tricky, and
it’s very easy to have short between
adjacent pins of fine-pitch devices. I
find a jeweller’s loupe is essential for
getting a close-up view.
Note: we received a follow-up email
that states: I just got the radio working! I decided to check the continuity
of connections to each pin of the display and ATmega chip. To be safe, I
removed the ATmega chip when doing
this test. All connections to the display
were fine. When testing the connections to the chip socket, I discovered
that I had not soldered two of the pins
for the encoder.
Fixing that, lo and behold, the radio
worked. The writing on the display is
visible only when I view it at an angle
of 45° or so. I see only white rectangles
when viewing it head-on. Adjusting
the contrast improved things somewhat, but viewing head-on, the writing
is not visible. I will fool around with
the contrast control some more. If it is
still not good, I will get a new display
from AliExpress.
Ways of mounting
ultrasonic transducers
The ultrasonic transducer I ordered
from your online shop (Cat SC5629)
to build the High Power Ultrasonic
Cleaner (September & October 2020;
siliconchip.com.au/Series/350) came
with a threaded steel ‘slug’. I searched
those articles and the internet for an
explanation of its purpose to no avail.
There is a tiny spike at one end of
the slug.
Also, given that the transducer has
a threaded hole in its face, do you
think that bolting the transducer to the
bath would provide better results than
using epoxy? (G. M., Hughesdale, Vic)
● Our suppliers didn’t give us any
instructions regarding those slugs
either; however, we think that they
are to plug the threaded hole in the
face of the transducer if it is not being
used to bolt the transducer to its mating surface. Doing so would slightly
increase the contact area between the
two surfaces, but we don’t think the
difference is enough to matter.
Still, it probably wouldn’t hurt to
insert the slug if you will be gluing
it to the surface. Just make sure to
thread it with the spike first, and turn
it until it is flush with the transducer’s face. The spike is just the result of
the way the slugs are cut from a longer
threaded rod.
SMD Test
Build it yourself Tweezers
● Resistance measurement:
10W to 1MW
● Capacitance measurements:
1nF to 10μF
● Diode measurements:
polarity & forward voltage, up to about 3V
● Compact OLED display readout
● Runs from a single lithium coin cell, ~five years of standby life
● Can measure components in-circuit under some circumstances
siliconchip.com.au
Complete Kit for $35
Includes everything pictured, except the
lithium button cell and brass tips.
October 2021 issue
siliconchip.com.au/Article/15057
SC5934: $35 + postage
siliconchip.com.au/Shop/20/5934
Australia's electronics magazine
March 2022 109
As for bolting the transducer on,
you certainly could do that, but you’ll
have to be careful drilling the hole
to avoid distorting the bath face and
clean up any burrs after drilling. The
surface needs to be very flat at the
mounting point. You’ll also have to
make sure it’s sealed properly so that
it can’t leak.
Keep in mind that when gluing the
transducer, the epoxy will fill in the
gaps between the two faces to ensure
good contact. Waterproof grease
smeared on the transducer’s face and/
or bath face is needed to provide a similar effect if you’re bolting it on.
Unexpected cause for
SC200 Amplifier fault
I hate having to ask for help, but I’ve
spent days on this and I need to move
on. My SC200 Amp (January-March
2017; siliconchip.com.au/Series/308)
has all the transistors in their correct
places. The soldering looks good, so
I don’t think there are any dry joints.
Transistor isolation from the heatsink
measures fine.
I’ve put 68W resistors in series
with the power supply connections,
as shown in Fig.14 on page 80 of
the March 2017 issue. I’ve used this
arrangement to successfully set up
Ultra-LD Mk.3 and Mk.4 amplifiers
in the past.
When I turn on the power, LED1
doesn’t light up, but LEDs 3, 4 and 5
do light up.
I spent a lot of time measuring voltages and couldn’t find the problem.
However, I noticed that if I put a DMM
probe in the area of the PCB around
the bases of Q3 and Q4, LED4 turns
off. About 10s to 20s later, LED4 turns
on again so that all LEDs are on. That
suggests a long time constant, possibly
associated with the 1000μF capacitor
in the feedback circuit.
If I put a DMM probe on the base of
Q8, LED1 and LED2 turn on, and LED4
turns off but begins returning to full
brightness almost immediately. That
said, sometimes when I switch it on,
all five LEDs turn on straight away.
With LED1 off at first turn-on, the
voltages across the safety resistors are
very low. With all the LEDs on, the
voltages are just less than 1V. There’s
no voltage across the output transistor
emitter resistors.
I tried disconnecting the feedback by
lifting one end of the 12kW feedback
110
Silicon Chip
resistor and earthing the base of Q2. In
this situation, LED1 turns on as soon
as power is applied, but all the other
LEDs are still illuminated. I’d really
appreciate any advice you can give
me! (D. H., Sorrento, WA)
● That behaviour is quite baffling and
suggests a major fault somewhere,
such as an open-circuit or short-circuit
transistor.
The fact that probing the base of Q8
causes things to change makes it likely
that the problem is around Q7 or Q8.
It’s almost as if the base of Q8 is floating. Check carefully around there. You
might want to consider replacing Q7
as it is easy enough to do. Also, look at
the 22kW and 2.2kW resistors and 1nF
and 150pF capacitors in that section to
verify they have the correct values, etc.
Note: we got a response a couple of
days later that read: this is embarrassing. Based on your advice, I decided
to re-check every joint and component from the input to the Vbe multiplier. With the benefit of more light
and a head-band magnifier, I got to the
10W resistor from input ground to 0V
and spotted a green ring. Somehow, a
10MW resistor had gotten into my bag
of 10W resistors!
I replaced it and all now works well.
I will measure all component values
in future.
More SC200
troubleshooting
I have been building your SC200
Amplifier project. I made two modules for a stereo amplifier. One module is working, but the other has some
problems.
The Clip Detector LED is active, and
considering the following measurements, I see it is working correctly.
I am using the 5W 68W resistors in
series with the power connection as I
am still testing.
I get the following measurements
using the CON2 power connection as
a reference:
• Positive rail: +55.9V
• Negative rail: -57.0V
• TP1: -54.2V
• TP2: -55.3V
• TP3 to TP7: all -54.3V
Removing fuse F2 makes no difference to the LED status. Green LED5
stays on while Red LED4 does not
turn on under any scenario. On the
other side, LED2 and LED3 work as
expected.
Australia's electronics magazine
Measuring around the circuit, I get
the following measurements.
• D2 A: -54.7V, K: -55.3V
• Q7 C: -6.87V, B: -54.8V, E: -55.3V
• Q8 C: -55.3V, B: -55.3V, E: -55.9V
• Q9 C: -54.3V, B: +54.7V, E: +55.2V
• Q10 C: -54.3V, B: -54.7V, E: -55.2V
• Q11 C: +56.0V, B: -54.2V, E: -54.8V
• Q12 C: -57V, B: -55.3V, E: -54.9V
I thought that Q8 might be internally
shorted between collector and emitter, but it does not measure as a short.
I have not replaced it, though. I have
checked the isolation between all the
devices and the heatsink.
Given the measurements above,
I thought there might be a short to
the negative rail; however, I cannot
find one. Do you have any thoughts
as to what would be the cause of
the unusual measurements? (B. D.,
Menangle, NSW)
● The reason that removing fuse F2
doesn’t cause the state of LED4 or LED5
to change is that the entire output stage
is being pulled to the negative rail, so
there’s never any significant voltage
across F2. What we need to figure out
is why that is happening.
It’s likely to be either due to Q9
not supplying any current (because
of a fault in Q9 or incorrect bias) or
Q8 being continuously switched on
(again, because of a fault or its biasing). You were on the right trail looking for shorts to the negative rail and
checking Q8.
Q9’s emitter is 0.7V below the positive rail, which is about right, indicating a collector-emitter current of 7mA.
So it is probably not at fault.
Q8’s base-emitter voltage of 0.6V
indicates that it is likely switched
on, perhaps too hard. Q7’s emitter
voltage indicates that it is supplying
enough current to Q8 to be responsible for this.
With the output pegged to the negative rail, Q2 should be switched on,
supplying current to Q4. As a result,
Q3 should also be sinking plenty of
current, preventing Q7’s base voltage from rising so high. We suggest
you check the voltages across the
68W emitter resistors of Q3 and Q4 to
verify that they are similar, indicating that both of these transistors are
likely working.
If that looks OK, it might be that Q1
is shorted or otherwise faulty and supplying too much current for Q3 to sink.
Some measurements of the voltages
continued on page 112
siliconchip.com.au
Advertising Index
AEE ElectroneX........................... 34
Altronics.................................75-78
Analog Devices............................. 9
Dave Thompson........................ 111
Digi-Key Electronics...................... 3
Emona Instruments.................. IBC
Hare & Forbes............................... 5
Jaycar.............................. IFC,53-60
Keith Rippon Kit Assembly....... 111
Lazer Security........................... 111
LD Electronics........................... 111
LEDsales................................... 111
Microchip Technology.............OBC
Mouser Electronics....................... 7
Ocean Controls........................... 10
PMD Way................................... 111
SC SMD Test Tweezers............ 109
Silicon Chip Shop............ 106-107
Silvertone Electronics................. 65
Switchmode Power Supplies..... 11
The Loudspeaker Kit.com.......... 67
Tronixlabs.................................. 111
Vintage Radio Repairs.............. 111
Wagner Electronics....................... 8
around Q1-Q4 would help to diagnose this fault further, but given that
they are inexpensive devices that are
relatively easy to replace, if you can’t
find a soldering problem or component
value error in that area, you could just
replace all four.
wide. This can also damage the ignition coil that could arc over internally
and short out the windings. That fault
is more difficult to check; the easiest
method is to swap the coil and see if
that fixes it (after checking the IGBT
using a resistance meter).
Jacob won’t climb his
ladder anymore
Modifying EA Active
Crossover frequencies
We bought our son a Jacob’s Ladder kit for Christmas. We separately
bought the coil recommended in this
kit.
Upon original completion, the kit
worked fine. While using it, it stopped
working and has not worked since.
We asked the retailer about this, and
they agreed that we had built the kit
correctly. Still, they were concerned
by the age of the kit on their shelves
(which they stated may have been
there for many years) and the possibility that components may have
dried out over this period, leading to
the failure.
Do you have any experience with
regards to which components regularly fail? (G. D., Redcliffe, Qld)
● Electronic components sitting on a
shelf should not fail after less than ten
years. The only parts that are likely to
age significantly are electrolytic capacitors, and we have plenty of 30-plusyear-old electros that are still fine.
Modern electrolyte formulas handle
ageing much better than much older
devices.
The semiconductors, resistors etc
will definitely still work.
Check fuse F1, which may have
blown. The most likely failure is
the IGBT (Q1). Usually, when these
fail, they end up with a short circuit
between the gate and collector (left
and centre pins) or the collector and
emitter (centre and right pins).
The IGBT is most likely to be damaged due to the spark gap being too
I recently came across several Twoway Electronic Crossover kits I started
assembling about 10 years ago that I
would like to complete. They were
sold by Altronics, Cat K5570.
The problem is that I have lost the
instructions that came with them.
Also, they were initially designed for
crossing between mid-high and high
elements. I would like to use them for
crossing over at 100Hz. Can you suggest the component values required for
sub-bass applications? (M. O., Croydon, NSW)
● Those kits are based on the Active
Crossover for 2-Way Speaker Systems project from Electronics Australia, May 1992. A scan of that article is available for purchase from
our website (siliconchip.com.au/
Shop/15/6072).
To change the crossover to 100Hz,
the component values can be scaled
using the original crossover frequency
versus resistor value tables. You can
change the 2043Hz value to 100Hz
by multiplying the resistor values by
10 and the C2-C7 capacitor values by
2.043.
So R2-R4, originally 39kW, become
390kW and R5-R7 become 470kW
(from 47kW). The original 2.2nF
capacitors can be 3.9nF in parallel
with 560pF (4.46nF total, within
1% of the required value of 4.49nF).
Capacitor tolerance (typically at least
±5%) will be the main cause of frequency shifts from the required crossover frequency.
SC
Notes & Errata
Vintage Radio, February 2022: the 100nF capacitor directly below the 6K8M valve in Fig.8 should connect to the GND rail instead
of the AGC line. In that same figure, there’s a 33μF 600V HT filter capacitor missing from the 250V rail to GND.
USB Cable Tester, November & December 2021: in the circuit diagram, Fig.1 on page 30 of the November issue, the numbers
for pins 8 and 10 on IC1 are swapped. Pin ANE2/RE2 connecting to USBU-GND via a resistor should be pin 10, while pin ANE0/
RE0, connecting to USBU-ID via a resistor, is actually pin 8.
The April 2022 issue is due on sale in newsagents by Monday, March 28th. Expect postal delivery of subscription copies
in Australia between March 25th and April 15th.
112
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
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