Technical Bulletin - Pakton Technologies

Technical Bulletin - Pakton Technologies
Pakton Technologies
sales@pakton.com.au
www.pakton.com.au
ABN 66 405 694 842
1 Helium Street
PO Box 408
Narangba Qld 4504
Tel: 61 7 3888 3793
Fax: 61 7 3888 4330
Technical resources for the after sales service
of Pakton products
Scope:
This document is intended for technicians who provide after sales service and repairs to
Pakton products.
Contents:

Disclaimer

What technical information is available on Pakton products

Technical expertise requirements

Terminology and Basic test methods as used in repair charts
Disclaimer
Electrical appliance repairs can be dangerous and should only be carried out by suitably
qualified persons. If in doubt seek advice from your local electrical safety authority. Pakton
Technologies will not be responsible for damages or injuries caused by the use or misuse of
this information.
Technical information
The following information is available to approved repair agents. The release of some of this
information may require the signing of a Non Disclosure Agreement.
The following documents are available from Pakton, request this by email:

Schematics

Schematic descriptions

Component overlays

Bill of Materials

Repair charts

Technical Bulletins
The following resources are available on line:
C:\Users\user\Desktop\Daily Backup\Technical resources for repairs.docx
Last Saved 11 Oct 2015
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Technical Resources for Repairers
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
Manuals – See http://www.pakton.com.au/support.php

Component specifications – See http://pakton.net/docsSecure/.datasheets.php
Good repair procedure
The basis of good electronics repair is the scientific method.

Observe the symptoms (gather facts)

Form a theory (based on the known facts)

Test the theory
Continue around this loop until you prove a theory and repair the appliance.
It is poor repair procedure to randomly replace components in the hope of finding the bad
one.
Divide and conquer. If there is a method of cutting a problem in halve, use it. For example if a
supply rail is low it could be a problem with the regulator (source) or it could be overloaded
(load). By cutting the track between the supply and the load you can split the problem up and
make it much easier to solve.
Compare to a known good. Taking the same measurement on a known good board can quickly
confirm whether that component is really bad, before you remove it from the PCB.
Write it down. Write down the facts, form a theory. There is no such thing as black magic, and
Ohms law always applies.
Walk away. Do not sit banging your head against a brick wall for too long. Put it aside, talk to
someone about it, it does not matter if they do not even understand electronics, it may help
you to talk it through.
Single fault assumption. If the appliance used to work properly, and now it does not. Logically
and statistically it should only have one fault. Avoid theories that involve more than one fault
unless there has been a lightning or similar surge, or someone else has worked on it before
you. It is possible, of course for one component failure to cause another in succession.
Lightning damage. Diode test every semiconductor, if you find most are dead then the unit is
probably beyond economic repair.
Moisture Damage. Clean and dry the PCB first. If you find fine tracks are corroded completely
away then this unit is probably beyond economic repair.
Arc Corrosion. If there has been any prolonged arcing inside the appliance enclosure you will
see degradation of plastics as if they have been under ultraviolet light and corrosion of some
metals as if it has been sprayed with acid. This unit is probably beyond economic repair.
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“It doesn’t work”. This is not a useful explanation of a fault. Get more information, preferably
from the owner.
Intermittent faults. These can be very difficult. Think about ways of making the fault occur.
Heat (hair dryer), spray freeze and vibration are possible methods. Look for bad or cracked
solder joints or “head on pillow” with surface mount devices.
Test Charts
These are available from Pakton
Terminology

Basic Level (Repair Chart) – Repairs which can be done without a schematic or CRO.
Basic level assumes the minimum set of tools and equipment as specified in the repair
chart. We do not expect people at this level to be looking at the debug data stream.

DMM or DVM - Digital Multi-meter. I.e, Fluke 17b.
Test Methods (Basic)

Measure AC Voltage. Set the DVM to measure AC voltage function to ṽ. Make sure the
range setting is higher than the expected voltage. Unless other stated this means to use
place the red lead (probe) at the requested point to measure (i.e. mains input) and the
black lead to the ground or neutral inputs. For more information click on this link.

Measure DC Voltage. Set the DVM to measure DC voltage or
. Unless other stated this
means to use a DVM to measure the actual DC voltage at the point i.e. pin 1 of IC1 with
respect to ground. I.e. place the negative lead of the voltmeter on circuit board earth,
ground plane or neutral inputs. For more information click on this link.

Measure maximum DC voltage. This is required to check the charge voltage on
capacitors. It requires a multimeter with a MIN,MAX function. Measure DC Voltage as
above and press the MIN,MAX button until MAX is shown on the screen.

Diode Test. Set the DVM to diode test function labelled ‘
’. Connect the red lead to
the Anode and the black lead to the cathode (the end with the stripe or K). The DMM
should read between 0.5 and 0.8 for working silicon diodes. When swapped it should
read high (open circuit). For more information click on this link.

Diode Test a NPN type Bipolar transistor. To test a NPN BJT transistor, connect the red
probe to the base. There should be between 0.5 and 0.8 when the black probe is on the
collector. Same for the emitter. When swapped it should read high (open circuit). Swap
red and black for PNP type.

Diode Test a MOSFET, In-circuit. Set the DVM to diode test function as above. Connect
the red lead to the Drain (metal top tab) and the black to the Source (right side lead). It
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should not read short circuit, the actual reading depends on the PCB. Reverse the red
and black leads and it should read between 0.5 and 0.8V as per a diode.

Diode Test an SCR, In-circuit. Set the DVM to diode test function as above. Connect the
red lead to the Anode (metal top tab) and the black to the Cathode (left side lead). It
should not read short circuit, the actual reading depends on the PCB.

Resistance Test an SCR, In-circuit. Set the DVM to resistance or diode test function.
Connect the red lead to the Gate (right side lead) and the black to the Cathode (left side
lead). It should read low, but not short circuit. The actual reading depends on the SCR
and the PCB. Compare with a working unit.

Continuity Test. Switch your DMM to resistance, ‘Ω ’ or
. Place the leads on either
end of the component, fuse or track you wish to test. Continuity (short circuit) - will
beep or read low. No continuity (open circuit) - will not beep and will show overload OL.
For more information click on this link.

Measure Resistance. Switch your DMM to resistance Ω. Place the leads on either end of
the component, fuse or track you wish to test. For more information click on this link.

Measure Capacitance. Switch your DMM to capacitance
. Place the leads on either
end of the component you wish to test. For more information click on this link. Usually
done with the component out of the PCB. In-circuit test readings are sometimes
possible, but rarely accurate.

In-circuit test. This means to measure (resistance, capacitance or Diode check) without
removing the component from the PCB. It is only possible in certain situations and the
reading may differ from that measure when the component is removed.

Lift one end. When an In circuit test is not possible you may remove one lead of a two
leaded component (such as a resistor or diode) from the PCB. A measurement done
with one lead isolated is the same as measuring the component removed from the PCB.

Lift a pin. On some surface mount IC’s it is possible (with due care and fine instruments)
to melt the solder and lift a leg.

Cut track. It is sometimes necessary to cut a copper trace in order to check to find which
component is causing a power rail to be over loaded. The track (or trace) is cut with a
fine blade to cause an open circuit. You can re-connect it using solder and or a fine
copper wire.

Discharge Capacitor. Use a 10 W wire wound resistor of approximately 500 Ohms to
discharge all capacitors. Soldering leads and probes or alligator clips to the resistor will
help make this safe to use.
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Common component pins
These pinout diagrams will help identify the leads of some of the components used.
TO-220 or TO-247 SCR
SOT23 Bi-polar transistor
MOSFET
Surface mount MOSFET
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