Saturday, November 27, 2010
Friday, November 26, 2010
Do it yourself coat hanger antenna
The secret of clear TV picture is the Quality of the Antenna .Most people believe that the more expensive the TV antenna is more powerful it is. That is not true, what matters is, does the antenna meet the basic design specifications.
In this video you will be shown how you can make a simple but powerful TV antenna cheaply using readily available coat hanger- why not try this project over the weekend.
In this video you will be shown how you can make a simple but powerful TV antenna cheaply using readily available coat hanger- why not try this project over the weekend.
Tuesday, November 23, 2010
Radio Dead on batteries (D.C) but work on 240 volts a.c)
This means there is something wrong on the dc line power supply. First I used my dc bench power supply and connected to the radio via ammeter (in series with the digital meter in amp range)
I noticed the meter has a high reading on ampere range. In fact it was 0.5 Ampere. (Normal current consumption of a radio should be between 0.06A and 0.08A)This is too high for a radio and therefore I suspected a heavy short inside the set on dc power line.
Usually when you find high current and nothing happens means that there is a short and the best way to know where the short is his to touch components on suspect areas and if any is getting hot then the problem is there.
After opening the set I followed the dc line and noticed the red positive wire joined together with the black wire negative. I confirmed there must have been a mistake there from the factory and fixed the wire to the right place and the set started working on the dc normally.
Conclusion
It is very important to measure current to the set because it can give a hint if the problem is short or open circuit even before you open the set.
If the current is zero expect an open circuit or component and if the current is high expect a shorted component.
First have a logical thinking to figure out what the problem is even before opening the set.
Also confirm the set is dead on both power sources (i.e. dc and ac power source) this can help you to know where the fault section is pretty first.
For example if a radio is hit by power surge in most cases only the transformer goes and this effectively cut off the power to the radio via the ac outlet but if you put batteries the radio will work and this is enough clue that the transformer has blown.
Repair tip
Before you open any equipment make sure you have gathered all the necessary information from observing the equipment and thinking logically where the problem is.
Then only open the equipment and go straight to the suspect circuit- do a thorough visual check for any suspect components-ie burnt components, visual check of all capacitors ie top swollen and also touching to feel any unusually hot components: this should be done even before doing any measurement.
Thank you guys
Let meet in the next class
I noticed the meter has a high reading on ampere range. In fact it was 0.5 Ampere. (Normal current consumption of a radio should be between 0.06A and 0.08A)This is too high for a radio and therefore I suspected a heavy short inside the set on dc power line.
Usually when you find high current and nothing happens means that there is a short and the best way to know where the short is his to touch components on suspect areas and if any is getting hot then the problem is there.
After opening the set I followed the dc line and noticed the red positive wire joined together with the black wire negative. I confirmed there must have been a mistake there from the factory and fixed the wire to the right place and the set started working on the dc normally.
Conclusion
It is very important to measure current to the set because it can give a hint if the problem is short or open circuit even before you open the set.
If the current is zero expect an open circuit or component and if the current is high expect a shorted component.
First have a logical thinking to figure out what the problem is even before opening the set.
Also confirm the set is dead on both power sources (i.e. dc and ac power source) this can help you to know where the fault section is pretty first.
For example if a radio is hit by power surge in most cases only the transformer goes and this effectively cut off the power to the radio via the ac outlet but if you put batteries the radio will work and this is enough clue that the transformer has blown.
Repair tip
Before you open any equipment make sure you have gathered all the necessary information from observing the equipment and thinking logically where the problem is.
Then only open the equipment and go straight to the suspect circuit- do a thorough visual check for any suspect components-ie burnt components, visual check of all capacitors ie top swollen and also touching to feel any unusually hot components: this should be done even before doing any measurement.
Thank you guys
Let meet in the next class
Friday, November 19, 2010
What is the future of electronics repairing?
A friend of mine who is a Salesman once told me this statement which still ringers in my mind like yesterday, we were taking a walk discussing and all of a sudden he told me these words” Humphrey my professor of economics told me that the first Sale is not important for the business but the second sale is very important”
Stunned by his words I asked him to elaborate further, and then he gave me this example...Suppose you have a small shop and a customer come to buy for the first time, the sale you make on his first visit is not very important in marketing world..So I asked him what is more important my learned friend…he told me the second visit/sale is very important because it means the customer was satisfied with your service.
This principal can be applied to every area of our life and because I am in electronics repairs and I believe most of you are let me apply it to electronics repairing business.
Suppose you have a repair shop, do you do your work to the highest standard so that you can keep your customers coming again and again or you are satisfied with the first visit only? A satisfied customer will always come back and bring more customers by referrals to your shop.
Statistics show that the best way of increasing your sales is not necessarily by increasing the number of calls but be keeping the customers you have coming back again and again.
When I joined the electronics world I was having one issue I wanted to deal with as a matter of urgency, to change the perception of customers toward the so called technician and I thought this was a Kenyan technician problem but sampling the emails I get across the world I have concluded that this problem is global.
For me getting my first repair was so hard to get but when I fixed the Television the customer was very satisfied and he referred to me yet another customer and when I went to collect the television he told me that he had no intension of having it 21 inch JVC repaired by a technician and whenever his equipment break down he buys a new one but he reluctantly accepted me to check it because his friend has convinced him that I can assist him by repairing his set.
So I was given a credit of doubt and I started working on the Television and it successfully came back to life, this was my second repair and since that time this customer has been coming to me whenever there is a problem with any electronics gadget in his house to date not mentioning many other referrals he make to me.
As technicians we have a collective responsibility to see that our services meet and exceed our customers’ expectations at all times, and by doing this we will keep our customers satisfied and keep on coming back with even more referrals.
The technology is changing at a very high speed and therefore a technician who want to remain relevant in today’s technology must be ready to invest on learning continually otherwise he or she might become irreverent pretty fast as far as repairs is concerned and therefore I urge my fellow technicians to set aside some money for personnel improvement in his/her area of specialization and also do some customer care courses to improve on his relationship with customers.
In conclusion my dear technician the future of electronics repairing is very bright for all of us if we are willing to listen to our customers and continually improve on our services in order to satisfy our customers at all times.
If you are willing to follow these basic steps...Then I will look for you at the top!
Any suggestion, comments and opinion of how you are dealing with this perception on technicians is most welcome. Also I would like to hear from customers/consumers about your experiences with the technicians near you.
Thank you guys
Let meet in the next class
Stunned by his words I asked him to elaborate further, and then he gave me this example...Suppose you have a small shop and a customer come to buy for the first time, the sale you make on his first visit is not very important in marketing world..So I asked him what is more important my learned friend…he told me the second visit/sale is very important because it means the customer was satisfied with your service.
This principal can be applied to every area of our life and because I am in electronics repairs and I believe most of you are let me apply it to electronics repairing business.
Suppose you have a repair shop, do you do your work to the highest standard so that you can keep your customers coming again and again or you are satisfied with the first visit only? A satisfied customer will always come back and bring more customers by referrals to your shop.
Statistics show that the best way of increasing your sales is not necessarily by increasing the number of calls but be keeping the customers you have coming back again and again.
When I joined the electronics world I was having one issue I wanted to deal with as a matter of urgency, to change the perception of customers toward the so called technician and I thought this was a Kenyan technician problem but sampling the emails I get across the world I have concluded that this problem is global.
For me getting my first repair was so hard to get but when I fixed the Television the customer was very satisfied and he referred to me yet another customer and when I went to collect the television he told me that he had no intension of having it 21 inch JVC repaired by a technician and whenever his equipment break down he buys a new one but he reluctantly accepted me to check it because his friend has convinced him that I can assist him by repairing his set.
So I was given a credit of doubt and I started working on the Television and it successfully came back to life, this was my second repair and since that time this customer has been coming to me whenever there is a problem with any electronics gadget in his house to date not mentioning many other referrals he make to me.
As technicians we have a collective responsibility to see that our services meet and exceed our customers’ expectations at all times, and by doing this we will keep our customers satisfied and keep on coming back with even more referrals.
The technology is changing at a very high speed and therefore a technician who want to remain relevant in today’s technology must be ready to invest on learning continually otherwise he or she might become irreverent pretty fast as far as repairs is concerned and therefore I urge my fellow technicians to set aside some money for personnel improvement in his/her area of specialization and also do some customer care courses to improve on his relationship with customers.
In conclusion my dear technician the future of electronics repairing is very bright for all of us if we are willing to listen to our customers and continually improve on our services in order to satisfy our customers at all times.
If you are willing to follow these basic steps...Then I will look for you at the top!
Any suggestion, comments and opinion of how you are dealing with this perception on technicians is most welcome. Also I would like to hear from customers/consumers about your experiences with the technicians near you.
Thank you guys
Let meet in the next class
Friday, November 12, 2010
Samsung Television dead
I received a phone call from a customer who wanted me to go and check his television which has developed a problem and was not working.
So I walked to his residence for that mission with a few tools: a multi meter which in electronics world is actually the eyes of the technician, I mean you can’t see electricity (voltage) with your own eyes but the meter can see and tell you if there is voltage or not and a screwdriver to open up the set.
The set was brought to me and I asked a brief history of the set especially the last moment before it died, I was told there was some smoke seen coming out of the set before they switched of quickly.
I didn’t intend to confirm that by powering it on again and therefore I opened the set and started scanning around the power supply looking for a component with catastrophic failure because I figured that since there was smoke, there must have some fire also and where there is fire there must be a heat mark or component swollen or broken to pieces.
Yes! I noted one capacitor with the top part swollen, the capacitor was rated 100uF/160V, in electronics sometimes if you don’t have the schematic you can have an idea of the voltage expected on any line by using the working voltage of the main filter capacitor of that line, for example usually when designing circuit the rule of the thumb is that the working voltage of the filter capacitor should be double the expected voltage on that line.
Therefore a capacitor rated 160 volts like the one above expect around 90 volts to 120 volts on that line, usually in television this capacitor with the 160Volts rating supply the B+ voltage to the fly back and therefore it is the main power on the secondary side of the power supply.
Next I decided to check the state of the fuse and it passed the meter test with flying colors, so I decided to apply power and do some voltage testing.
I applied power and to my surprise nothing happened, no smoke so I concluded that whoever said that he switched off after seeing the smoke did it a little too late.
So I started my voltage testing, with my meter negative probe on the main capacitor negative pin, I started to test the voltage at the actual main capacitor and there were zero Volts …Nothing!
Hint: when you get zero volt on a circuit means there must be an open circuit or component but not a short, usually a short causes voltage to go low and pulsating(at least there must be some funny reading on the meter)
I checked the ac voltage across the power cable input connector on the circuit board and found 220 vac, so what is preventing the voltage from reaching the main capacitor.
So I checked backward from the main capacitor looking for any open component or circuit cracked, from the testing I noted that the surge limiter is open circuit.
After this I decided to take the television with me to the work shop for further testing, at least now I have some clues to the problem.
I replaced the two component and applied power using my homemade series bulb and I noted that the bulb was lighting with intense light.
I concluded there must be a shorted component on the supply and therefore I switched off and started touching component around the power supply looking for any which is getting very hot. I bumped on one high wattage resistor which was too hot to my fingers.
So I concluded that I have a bigger problem than I estimated, the TV was quite old and was using I.C STR50103A as the regulator and because I could not get the circuit diagram of this TV I rushed to my friend Google and I got this data sheet.
Before I went for the datasheet I had taken the voltage testing of this i.c and was as follows:
Pin 3 is the main dc in from the main capacitor, I was expecting around 300 vdc but I can only measure 252 vdc.
Pin 4 is the output of B+ to the horizontal circuit, please note this tv is very old and therefore is using series type of switch mode power supply. Here again I was expecting around 100 volts consindering the filter capacitor on that line is rated 160 Volts.
That why I decided to check on the datasheet for this ic to get the expected voltages on those pins and this is what I got:
Pin 3 is 282 Volts (around 300 vdc on 220 vac outlet or 155 vdc on 110 vac outlet) and pin 4 the output to the horizontal circuit is 118 vdc but this has gone up to 250 volts.
Now you can see why this B+ capacitor has to blow is due to this increased voltage on that line(from 118 volts to 250volts)
With that I concluded that this ic STR-50103A must have gone forever, looking at that ic internal structure you can see two transistors and I concluded that one must have shorted collector emiter and therefore instead of doing his work has a regulator it is acting just like a jump wire.
I replaced this ic plus the surge limiter and the blown capacitor and powered again the set via series bulb and the machine came back to life.
Just before I went into celebrations for the job well done I noticed that the picture was very clear(like digital picture but no audio)
I was not told about this before so I conforted myself that may be there is sound mute via remote control and started looking for one from the owner and they told me that it got lost over 10 years ago and therefore they have been using only the keys.
I opened the set again this time looking for the audio circuit of this set and it was not easy to locate because I was looking for an ic bolted on an heat sink only to find that this TV is using discrete components for the audio circuit.
I started doing some voltage testing not sure how much voltage to expect because I could not locate the circuit diagram for this television.
Then by coincidence when following a 110 volts from the underside of the circuit I noted a pin with 110volt and zero volt on the other leg. This component is in series with 110 volt so how can it be zero volt, I turned the board the other side and I saw the component was white in color and from the circuit it was marked as a fuse.
Took a resistance test on it and it turned out to be open and I was very sure this could be the end of my woes and indeed it was the cause and after replacing it and powering the set I liked what my ears heard…
Thank you guys
Let meet in the next class
So I walked to his residence for that mission with a few tools: a multi meter which in electronics world is actually the eyes of the technician, I mean you can’t see electricity (voltage) with your own eyes but the meter can see and tell you if there is voltage or not and a screwdriver to open up the set.
The set was brought to me and I asked a brief history of the set especially the last moment before it died, I was told there was some smoke seen coming out of the set before they switched of quickly.
I didn’t intend to confirm that by powering it on again and therefore I opened the set and started scanning around the power supply looking for a component with catastrophic failure because I figured that since there was smoke, there must have some fire also and where there is fire there must be a heat mark or component swollen or broken to pieces.
Yes! I noted one capacitor with the top part swollen, the capacitor was rated 100uF/160V, in electronics sometimes if you don’t have the schematic you can have an idea of the voltage expected on any line by using the working voltage of the main filter capacitor of that line, for example usually when designing circuit the rule of the thumb is that the working voltage of the filter capacitor should be double the expected voltage on that line.
Therefore a capacitor rated 160 volts like the one above expect around 90 volts to 120 volts on that line, usually in television this capacitor with the 160Volts rating supply the B+ voltage to the fly back and therefore it is the main power on the secondary side of the power supply.
Next I decided to check the state of the fuse and it passed the meter test with flying colors, so I decided to apply power and do some voltage testing.
I applied power and to my surprise nothing happened, no smoke so I concluded that whoever said that he switched off after seeing the smoke did it a little too late.
So I started my voltage testing, with my meter negative probe on the main capacitor negative pin, I started to test the voltage at the actual main capacitor and there were zero Volts …Nothing!
Hint: when you get zero volt on a circuit means there must be an open circuit or component but not a short, usually a short causes voltage to go low and pulsating(at least there must be some funny reading on the meter)
I checked the ac voltage across the power cable input connector on the circuit board and found 220 vac, so what is preventing the voltage from reaching the main capacitor.
So I checked backward from the main capacitor looking for any open component or circuit cracked, from the testing I noted that the surge limiter is open circuit.
After this I decided to take the television with me to the work shop for further testing, at least now I have some clues to the problem.
I replaced the two component and applied power using my homemade series bulb and I noted that the bulb was lighting with intense light.
I concluded there must be a shorted component on the supply and therefore I switched off and started touching component around the power supply looking for any which is getting very hot. I bumped on one high wattage resistor which was too hot to my fingers.
So I concluded that I have a bigger problem than I estimated, the TV was quite old and was using I.C STR50103A as the regulator and because I could not get the circuit diagram of this TV I rushed to my friend Google and I got this data sheet.
Before I went for the datasheet I had taken the voltage testing of this i.c and was as follows:
Pin 3 is the main dc in from the main capacitor, I was expecting around 300 vdc but I can only measure 252 vdc.
Pin 4 is the output of B+ to the horizontal circuit, please note this tv is very old and therefore is using series type of switch mode power supply. Here again I was expecting around 100 volts consindering the filter capacitor on that line is rated 160 Volts.
That why I decided to check on the datasheet for this ic to get the expected voltages on those pins and this is what I got:
Pin 3 is 282 Volts (around 300 vdc on 220 vac outlet or 155 vdc on 110 vac outlet) and pin 4 the output to the horizontal circuit is 118 vdc but this has gone up to 250 volts.
Now you can see why this B+ capacitor has to blow is due to this increased voltage on that line(from 118 volts to 250volts)
With that I concluded that this ic STR-50103A must have gone forever, looking at that ic internal structure you can see two transistors and I concluded that one must have shorted collector emiter and therefore instead of doing his work has a regulator it is acting just like a jump wire.
I replaced this ic plus the surge limiter and the blown capacitor and powered again the set via series bulb and the machine came back to life.
Just before I went into celebrations for the job well done I noticed that the picture was very clear(like digital picture but no audio)
I was not told about this before so I conforted myself that may be there is sound mute via remote control and started looking for one from the owner and they told me that it got lost over 10 years ago and therefore they have been using only the keys.
I opened the set again this time looking for the audio circuit of this set and it was not easy to locate because I was looking for an ic bolted on an heat sink only to find that this TV is using discrete components for the audio circuit.
I started doing some voltage testing not sure how much voltage to expect because I could not locate the circuit diagram for this television.
Then by coincidence when following a 110 volts from the underside of the circuit I noted a pin with 110volt and zero volt on the other leg. This component is in series with 110 volt so how can it be zero volt, I turned the board the other side and I saw the component was white in color and from the circuit it was marked as a fuse.
Took a resistance test on it and it turned out to be open and I was very sure this could be the end of my woes and indeed it was the cause and after replacing it and powering the set I liked what my ears heard…
Thank you guys
Let meet in the next class
Friday, November 5, 2010
How to troubleshoot CRT Television switch mode power supply problems (s.m.p.s)
Most problems with equipment using switch mode power supply (s.m.p.s) like television and monitor are power related, this is because power supplies runs under considerable stress due to high voltages and current involved around these circuits.
In order to understand how to solve s.m.p.s problem I am going to show you how to analyze common failure mode in CRT television, you can use this principle in repairing CRT monitor too.
Case One: CRT Television Dead
Here dead I mean the set does not show any sign of life, power ON LED is not lighted and nothing happens even after power is switched on.
First confirm the television power cable is not broken inside, you can check this by measuring the voltage across the AC power input connector on the circuit board.
If the voltage is reaching the circuit board, then look for the fuse and see if it is blown, if the fuse is okay check also the surge limiter is open or not.
If these two components are okay then most likely there is no short on the primary side of the power supply.
Short in the primary side of the power supply usually cause the surge limiter or the fuse to blow.
From now on we shall be using the main capacitor negative as the Ground for all the measurements of the voltages on the primary side of the power supply.
I have modified my meter ground probe with a crocodile clip so that I can attach it to the ground point of the equipment I am repairing and therefore I use only one hand to probe the circuit.
This is safety precaution because as you know for there to have a potential difference there must be a connection between the live and the ground.
So if you are using your two hands and incidentally touch the live and the ground then the current will flow through your body and this can be fatal. But if you are using one hand it is not possible.
One thing I have learn in electronics is that if you master doing your troubleshooting using voltage tests you will have an added advantage because in electronics it is not always the component that fail but it could be just a crack on the circuit board that is preventing the voltage to flow or even dry joints and therefore if you concentrate on looking for the bad component you are going to waste a lot of time and end up not repairing the set.
Therefore I encourage you to narrow down to the faulty circuit (area) by using voltage testing only. This one is very fast and valuable method I have come to learn.
Now set your meter to DC range of 1000VDC and use the main capacitor as your ground.
First check the voltage across this main capacitor and if you get around 300 vdc on 220vac outlet or 150 vdc on 110 vac outlet then it is assumed the supply is okay up to the main capacitor.
If there is no voltage at the main capacitor then check backward looking for open component or circuit board cracked or dry joint on the power path.
Be sure this main DC(300vdc or 150vdc) is reaching the power regulator ic collector/drain pin, Now still using the same ground move the positive probe and measure the vcc-IN pin of the power regulator ic.
Depending on the regulator used you can check the correct vcc-IN Supply (start up Voltage) from the data sheet for the ic used from the internet.
These two voltages are very important and if any is missing the supply will appear dead, if the vcc-IN is missing this means there is a open circuit or start up resistor is open.
Follow backward and find what is preventing the start up voltage from reaching the vcc-IN pin.
Another hint: if you see this vcc is less than normal and pulsating there is a possibility that there is a short on that pin, to confirm just lift up that pin and if the voltage increases then it means there is a short on that pin internally and the ic must be replaced.
There is also a filter capacitor for this source usually 100uF/35V, please check the ESR of this capacitor or directly replace it if you don’t have an ESR meter.
There is also a resistor linked to the source pin of this ic called the current sense resistor which sometimes open or change value and this can cause the power supply not to start. Usually it is a very low ohm resistor, less than 2 ohms and around 2 watts so it is a big one.
If up to here you have checked and everything is okay, then you should suspect a short on the secondary side of the s.m.p.s.
First measure for short of any of the secondary diode using analogue meter set to X1, when you measure across any diode on the secondary you should not have two reading and if you get two reading lift up one leg and test again. If you still get two reading then you can conclude that diode is shorted.
Also when using this method and find that the diode has two reading in-circuit and when lifted up you get one reading, it could also mean there is a short on that source (line).
You can follow that source looking for the shorted component; usually the most common components to short are transistors, ics, diodes, capacitors.
Remember when doing voltage testing on the secondary circuit you should be using the COLD GROUND of the set.
The best cold ground to use is the turner ground (out part) or the CRT ground return.
If you find still there is no voltage at the secondary output or the voltage is low, it is the time to substitute for the main B+ Load with a dummy load.
You can make a dummy load by using a 40 watts bulb/250 vac, a bulb holder, crocodile clip and a wire(read and black) and connect them as shown on the picture below.
Now identify the main supply to the fly back called the B+ and disconnect the supply just before the fly back B+ vcc pin. Don’t cut the circuit board to do this just lift up one side of a resistor( high wattage) in series with this B+ voltage or sometime they use a jumper wire just before the B+ vcc pin of the fly back and attach your dummy load between this point and the cold ground.
If the bulb light steadily and you measure between 90 Volts dc to 140 dc depending on the size of the television then you can assume that the s.m.p.s is okay and the problem is on the secondary side.
For those who want to be expert in Switch mode power supply(S.M.P.S) repair i personally recommend this book by Jestine Yong...i have personally read it and added a few tricks to my arsenal..click on the book for more info on how to have it on your workbench.
Recommended books
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