Small switch mode power supplies modification secrets

Assuming you already have the universal external power module and beforeinstallation you need to remove the power IC and the power FET and make surethe below components are good:Main Fus

Small Switch Mode Power Supplies

Modification Secrets

Brought to you by Jestine Yong

Copyright@ All Rights Reserved

Warning! This is a copyrighted material; no part of this guide may be reproduced or transmitted in any form whatsoever, electronic, or mechanical, including photocopying, printing, recording, or

transmitting by any informational storage or retrieval system without expressed written, dated and signed permission from the author You cannot alter, change, or repackage this document in any manner.

Jestine Yong reserves the right to use the full force of the law in the protection of his intellectual property including the contents, ideas, and expressions contained herein Be aware that eBay actively cooperates in closing the account of copyright violators and assisting in the legal pursuit of violations.

DISCLAIMER AND/OR LEGAL NOTICES

The reader is expressly warned to consider and adopt all safety precaution that might be indicated by the activities herein and to avoid all potential hazards This E-book is for informational purposes only and the author do not accept any responsibilities or liabilities resulting from the use of this

information While every attempt has been made to verify the information provided here, the author cannot assume any responsibility for any loss, injury, errors, inaccuracies, omissions or inconvenience sustained by anyone resulting from this information Most of the tips and secrets given should only be carried out by suitably qualified electronics engineers/technicians Please be careful as all electrical equipment is potentially dangerous when dismantled Any perceived slights of policy, specific people

or organizations are unintentional.

Limit of Liability / Disclaimer of Warranty:

The authors and publisher of this book and the accompanying materials have used their best efforts in preparing this program The authors and publisher make no representation or warranties with respect

to the accuracy, applicability, fitness, or completeness of the contents of this program They disclaim any warranties (expressed or implied), merchantability, or fitness for any particular purpose The reader is expressly warned to consider and adapt all safety precautions that might be indicated by the activities here in and to avoid all potential hazards By following the instructions contained herein, the reader willingly assumes all risks in connection with such instructions The authors and publisher shall in no event be held liable for any loss or other damages, including but not limited to special, incidental, consequential, or other damages As always, the advice of a competent legal, tax,

accounting or other professional should be sought.

This manual contains material protected under International and Federal Copyright Laws and Treaties.

No parts of this manual shall be reproduced or transmitted by any means, electronic, mechanical, photocopying, printing and recording or otherwise Any unauthorized use of this material is

prohibited All product illustration, product names and logo are trademark of their respective

manufacturers.

Small Switch Mode Power Supplies Modification

Secrets

2 True Case Histories 1

3 True Case Histories 2

4 True Case Histories 3

6 Conclusion

Small Switch Mode Power Supplies Modification Secrets

This small switch mode power supplies modification worked superb Iteliminates your headache in solving many different types of power suppliesproblems Check out the advantages again in solving the below problems:When there is lightning strike on the power supply, usually there will besome bad components In some cases the power side components couldburn beyond recognition If there is no schematic diagram or same model

of power supply to compare to locate the original parts value, it would betough to repair the power supply

The power IC and power FET in power supplies come with many

different types of part numbers If you can’t locate either one of the partsthis mean you will not be able to repair it

Save cost- In some power supplies the price of power IC and the powerFET can be quite expensive You no longer have to keep stock for varietypart numbers for power IC and power FET This modification method cantruly save the cost

Save time- Sometime we spent too much time in troubleshooting the

power supplies Problems like no power, low power, too high power,

power shut down, intermittent power problem and etc can be solved by

using the method that I’m going to show to you as you read on

Easy to follow- It can be done in less than 20 to 25 minutes if you follow

my steps

The most important thing is the parts are quite cheap and you can checkout where to buy the parts at page 39

True Case Histories 1

A customer sent to me a 22” Benq LCD Monitor (G2220HD Model) with the

complaint of no power He told me someone had tried repair it before butunsuccessful The moment I opened the cover I saw the power IC was missingand I do not know what the original part number was The power FET shortedand part of the current sense resistor outer layer also came off (see the photobelow and next page)

Power/Inverter Board with missing Power IC- Figure 1

Missing Power IC and Current Sense Resistor Cracked- Figure 2Finding the original schematic in order to look for the original part (power IC)will not be easy Even if you could find the power IC you still have to proceed

to buy the parts, replace the power FET and check all the primary side

components and make sure they are all good This also will not guarantee thepower supply will come back to life after it had been badly repaired by

someone Precious time will be lost doing a repair work that had been done by

others In my opinion the best solution is to modify with a universal external

power module onto it How this can be done? Check the photos in the next

page and read the step by step explanations

Universal External Power Module- Figure 3

Universal External Power Module-Figure 4

Assuming you already have the universal external power module and beforeinstallation you need to remove the power IC and the power FET and make surethe below components are good:

Main Fuse

Bridge Rectifier

Main Filter Capacitor

Power Transformer primary winding

Optoisolator IC

Secondary output diodes and

Secondary filter capacitors (made sure the capacitors are not bulged)Note: For main fuse, bridge rectifier, Optoisolator IC and secondary outputdiodes you can use a normal analogue multimeter to test Filter capacitors youcan useESR meterto test and Power transformer (primary winding) you canuseBlue Ring Testerto check it If you do not have a Blue Ring tester no

worries because usually the primary winding of power transformers are quite robust and rarely have problem.

The primary winding is the pins of the drain of power FET (center leg) and thepositive (+) leg of main filter capacitor and it should show 8 LED light as

shown in the photo in the next page:

Identifying the Power Transformer Primary Winding Legs- Figure 5

Note: In some smaller power supplies the Blue Ring Tester only registered 5 to

7 LED lights on the transformer primary winding

Besides the above components, you are also required to check on the

corresponding components in the power supply especially the semiconductorslike diode, zener diode and transistor (if have) and made sure they are good Thereason to check all these components is to prevent the newly install universalexternal power module from not working or blowing caused by the shortedcomponent/s I just mentioned

Assuming all of the components mentioned above tested good, you now canbegin to install the universal external power module Apply some heat

compound to the module before fitting it to the heatsink See the photo in thenext page

Apply heat compound before fixing the module to heatsink- Figure 6Since there is no extra hole for the 5 wires from the power module to passthrough, you may need to use a drill to make a hole on the circuit board as seenfrom the photo below:

Drill a small hole so that the power module wires can be inserted- Figure 7

Note: Make sure the drill did not break any circuit track behind the board.

Please refer to the diagram below on the connection of the 5 wires:

A typical power supply schematic diagram to show where the 5 wires need to be

connected- Figure 8Black wire- Connect to the negative leg of Main filter capacitor

Green Wire- Connect to the positive leg of Main filter capacitor

Red Wire- Connect to the Run DC circuit output (after the Run DC diode)White wire- Connect to pin 4 of Optoisolator IC (make sure the circuitline is cut-more details in the next page)

Yellow Wire- Connect to the drain pin of Power FET (Make sure youremove the power FET

Note: Remember to remove the power IC and power FET from the power supply board

Next step is to cut the pin 4 circuit track of Optoisolator IC so that the externalcircuitry would not affect the operation of the Optoisolator IC

If you refer to the diagram in figure 8 again you will notice that the Optoisolator

IC pin 3 is not going to hot ground (some other circuits are going to hot groundlike the one below):

A typical SMPS Optoisolator IC pin 3 connected to hot ground- Figure 9

Since the board that I’m modifying, the pin 3 of Optoisolator IC did not go to

hot ground thus I have to cut away the circuit line and connect a wire betweenpin 3 and hot ground as seen from the photo in the next page:

Connection of Optoisolator IC pin 3 to hot ground- Figure 10

This is how the 5 wires are connected in the power supply board- Figure 11

Modification Completed- Figure 12Once done soldering the 5 wires, please recheck your work Before you turn thepower supply On solder a 100 watt light bulb on the fuse points so that if there

is any error in fixing the wires, the power module would not blow If the powermodule blows you will waste your precious time and have to redo everythingagain

Note: Please refer to page 26 on how to connect the bulb

If the power supply is working the fuse would not light up and you will get tomeasure the two output dc voltages In this example the output voltages were 5

volt and 19 volt If you have confirmed the power supply is working fine

then you have to do a proper wiring work as seen in figure 36, 37 and 38.

Once done on the wiring work and powered On this is what I saw-see next page

A dead power supply was brought back to life- Figure 13

True Case Histories 2

A friend of mine who have some experience in electronics repair brought in a

LG 17” LCD Monitor and showed to me the burnt power IC of the power

supply He asked if I could repair it and I told him no problem He actuallywanted to repair the power supply himself but because of the burnt power IC hegave up

Note: It is not easy to repair the power supply especially if you can’t identify the

part number and can’t get the original schematic diagram

Burnt power IC found in this 17” LCD Monitor power board-Figure 14

For your information this power supply design does not have power FET This

means it only uses one power IC Even though it only uses one power IC, themodification method still works

Note: This is why having this ebook you will have advantage over other repair

technicians that do not know this method of modification

A typical Power Supply schematic that uses one power IC (for your

reference)-Figure 15

As usual, before you start to use the universal external power supply modulehere are the things that you need to check first:

Main Filter Capacitor

Power Transformer primary winding

Optoisolator IC

Secondary output diodes and

Secondary filter capacitors (made sure the capacitors are not bulged)

Note: Main fuse, bridge rectifier, Optoisolator IC and secondary output diodesyou can use a normal analogue multimeter to test Filter capacitors you can use

ESR meterto test and Power transformer (primary winding) you need to use

Blue Ring Testerto check it If you do not have a Blue Ring tester no worries

because usually the primary winding of power transformer rarely have problem.

In this model that never use power FET, the primary winding are the pins of thepositive (+) leg of main filter capacitor and the next pin It should show 8 LEDlight as shown in the photo in the next page:

The burnt power IC also affected the back circuit track- Figure 17Blue Ring Tester showing 8 LED lights when checking on the transformer

Primary winding –Figure 16

If there are parts that found to be bad, make sure you replace it first before youstart your modification work In this power supply, besides the burnt power IC, Ialso found the main fuse open circuit Once you have confirmed all the otherparts are good then start the modification work.

Drill a hole so that the 5 wires of the universal power module can pass

First break the circuit track that is leading to the pin 3 and pin 4 of theOptoisolator IC.

You can use a pen knife to cut the circuit track- Figure 19

Here are the 5 wires of the Power Module coming out from the hole that I have

drilled- Figure 20

The function of each wires- Figure 21

Black wire- Connect to the negative leg of Main filter capacitor

Green Wire- Connect to the positive leg of Main filter capacitor

Red Wire- Connect to the Run DC circuit output (after the Run DC diode)White wire- Connect to pin 4 of Optoisolator IC (make sure the circuitline is cut)

Yellow Wire- Connect to the drain/output pin of Power IC (Make sureyou remove the power IC

Modification Completed- Figure 22

In order to be in the safe side, once you have fixed in everything, please connect

a 100 watt bulb across the fuse (with the fuse removed) and power On A goodpower supply the bulb will go off and you will get the output voltages In the

test I’ve got 5.15 V and 12.60 outputs which indicate the power supply is

working If the bulb glows with full brightness this means there is somethingshorted or you have connected the 5 wires wrongly and you need to turn thepower supply off and recheck the connection again

12.6 volt output- Figure 245.15 volt output- Figure 23

Once you have tested that the power supply is working fine you can actually

redo all the 5 wires soldering and do a proper wiring before closing back the cover You can refer to figure 36, 37 and 38 to see how I have properly done

a nice work on a DVD player power supply

There you are, simple and fast modification that always work

Power supply working perfectly good- Figure 25

True Case Histories 3

The complaint of the AKIRA DVD player was no power but the main fuse wasgood This power supply design use only one power IC and the power FET isbuilt into the Power IC

The Akira DVD Player Internal boards Figure 26

The Akira DVD player power supply unit- Figure 27When I checked on the output diodes there was no output voltage even after allthe connectors from power supply to the mainboard were pulled out.

Sometimes a shorted component in the mainboard could cause no power

symptom so removing all the connectors is just one of the procedures in powersupply troubleshooting I did not check the bridge rectifier because the mainfuse did not blow

I proceeded to check on the main components The first thing I did was todischarge the main filter capacitor-see next page