A, AF, AX, D, DF, DX Version of HOT

If you repair CRT Monitor I’m sure you might have came across Philips Horizontal output transistor (HOT) that have many version behind each part number. For example, BU2508A, BU2520AF, BU 4522AX, BU4523DX and etc. For your information the A version does not have a built in damper diode but the D version have damper diode in it. You may refer to semiconductor databook or from the internet to see the specification of each HOT.

The question is, could an A version be replaced by the D version and vice versa? I understood that many repair technicians replaced the A version with the D version and did not replace the D version with the A version. The reason was that the HOT with a built in damper diode is much better than the HOT without damper diode in it. Yes, it is true that many of the Monitor in the market with the A version can be replaced with the D version but i did came across certain brand of Monitor that only can run well with the original part number! That means, the D version would not last. It worked for only a week or two before the HOT blow again. Putting back the A version solved the problem.

Since HOT is easily available from the market, i suggest that you put back the exact part number to avoid call back because a repeated repair is a loss to you and your business

Power Supply Blow Again After Sometime

If you have replaced power components (be it a power IC or power FET) and the power supply blow again after sometime, then i suggest that you check on the secondary side. The secondary side that I’m referring to is the legs of the power transformer. I came across the power transformer secondary pins that had intermittent dry joints problem and the power supply could work (may be few hours ) but after that it will blow again. It is interesting to know that the blown parts were exactly the one that were replaced earlier. It will cause overvoltage, because no load at the secondary side. This tiny dry joints were quite hard to see and if possible get a magnifying glass to help you out.

Sometimes it can be your fault too because you did not apply the heat compound to the power IC (power IC that attach to heatsink) or even to the power FET. Always check corresponding components if you found that the power FET had shorted

Schematic Diagrams Website

One of my reader Ray suggested that i put up a category of schematic diagram website since there are so many blog readers asked about schematic diagrams. Whether the websites will impose for a fee or a free schematic diagrams website like eserviceinfo.com i would like you to let me know so that i could compile those websites into this blog for easy reference. Please click on the famous free schematic website below to look for the schematic that you need

Open Winding In Yoke Coils

Well, I’m not sure about you and as for me so far after so many years in this repair line i had only came across only few PC tube that have open winding in yoke coils. It seems that yoke coils are more prone to short circuit compare to open winding. Horizontal yoke coil get shorted easily compare to vertical yoke coil most probably due to stress from the higher voltage and current to the winding. By using a normal ohm meter you could easily check if the winding is open circuit or not. To check for shorted winding in horizontal yoke coil, one have to use a Blue Ring tester.

If either one of the coil have problem (in a color picture tube) the best is to replace the whole picture tube. Yes in fact you can just replace the coil but you have to spend lots of time to adjust the convergence. The display you might get could be color patches all around the tube if you have decided to replace only the yoke coil. I suggest that you replace the pc tube in order to save time

Open Circuit In Heater (Filament) Of CRT Tube

After so many CRT Monitors sent in for repair, i could say that i only came across one unit of a 14″ Acer Monitor that had an open winding in the filament (heater). The complaint was no display but have high voltage and i found that the heater was present but there was no glow in the filament. Checking the filament with an ohmmeter revealed that in fact the filament already had an open circuit internally. This is very uncommon and normally the filament is quite robust.

Do you know that our filament could take about 10 to 11 volt? A normal tube is using 6.3 volt dc and by increasing the heater voltage one can bring back a tube to life but again it depends on how severe is the tube. I had done an experiment before many years ago where i deliberately increase the heater voltage to see what voltage the filament could withstand. I tested it by using my adjustable power suppl. Increasing the voltage up to 11 volt seems to be still okay but when i set to 12 volt dc, the filament immediately break.

Now, if you ever come across any tube that have dim display and you have confirmed that the tube already weak then modify a circuit that can only go up to 10 volt. 11 volt could be marginal and the best is from 8 to 10 volt. 12 volt will surely burn up the filament. If you have the time and a bad tube (winding shorted and etc) then you can do the experiment yourself and see how is the outcome. You will see that the filament will glow extra bright before it burn out

Shorted Degaussing Coil

So far i have not come across any shorted Degaussing coil before but i do came across a leak (black tape open) degaussing coil that touches the cold ground (the metal that locked the PC Tube) that had caused the ELCB to trip whenever you apply the AC power. If you need to check on the condition of this coil, you can use a Blue Ring Tester to check it and it should have many LEDs lit. Assuming if the degaussing coil have problem you can always salvage another good coil from a junk Monitor and use it

Electric Shock From Heatsink

During my early day in Monitor repair there was an old NEC 14″ CRT monitor that came in for repair with the complaint of no power. Since i donot have the original part number i had use a substitution part number. After the replacement of the HOT (not original part number) i wanted to test whether the new substitution HOT would work or not, i used my finger to touch on the heatsink. I did not expect that i would get a shock from the heatsink! My finger developed a sharp pain and it lasted for few hours. Normally by touching on the heatsink or the HOT one would know if the substitution HOT will last long or not.

I began to inspect why the HOT heatsink could have current in it. Later i found that this design actually have the HOT collector (the HOT metal plate body) directly connected to the heatsink. In many Monitors, usually the heatsink is the cold ground. I had learned my lesson from that day onward that do not simply touch any electronic parts in it if you are not really sure of what you are touching

Looking At Color Test Pattern Software

There was one time a friend of mine came into the technical department and jokingly said “why when every time i visit your place you keep on looking at the test pattern, don’t you have nothing else to see at the computer screen?”. For your information we as Monitor repairer have to depends on the Monitor test pattern software to identify the fault. This repair job is not like repairing Audio equipment where you have to listen to the sound. The good thing about the Monitor test pattern is that whenever anything wrong with the circuit, you could see that the test pattern will change for example a missing colour, one horizontal/vertical line, sync out, small/big width and etc. From the display problem shown, and if you have the experience you can actually go straight to the exact circuit location. For example, a missing red color will prompt you to check on the VGA cable, CRT board and straight to the RED circuitry.
Without a test pattern software we may have some difficulty in identifying certain problem like colour problem, jagged linesa and etc. Yes you can always run the Windows display but with the test pattern you could instantly know what is actually wrong with the Monitor be in the LCD or CRT Monitor. Search from Google about this testing sofware and i’m sure will easily find one

Photo Of The Internal Part Of A CRT Monitor

If you wish to learn more abou the CRT Monitor repair please click on the photo to visit Sam Goldwasser website

High Tension Or High Voltage

Have you heard of any of your repair friends that says there is no high tension in the Monitor/TV? Some of my repair friends refers the flyback transformer section as High tension section while to some they just called it as High voltage section. So which one should you use, high tension or high voltage? Actually for those who are a seasoned electronic repairer whenever someone say high tension or high voltage, you will automatically know that they was referring to the flyback transformer area/section.

If you are new in this repair field i guess you stick to high voltage section-why? According to the Stan Gibilisco Electronics Dictionary Boo, high tension means “Pertaining to utility power-transmission lines on which there are very high voltages, typically 100 kilovolts (100 kv) or more” while the meaning of high voltage ” In a cathode ray tube, the voltage that accelerates the beam electrons”

Since the high voltage produced by the flyback transformer is only about 24 Kv (less than 100 Kv) then the best word to describe about the flyback transformer area is the “High Voltage

Always Check Corresponding Components

Now in troubleshooting it is not always only one component that give problem. I used to receive email saying that they have found the bad component and after the replacement the power section or the HOT blow again. In certain electronic problems, there are usually few bad components that made a section malfunction. That means just by replacing a bad components would not solve the problem. One must check for other components too.

For example, if you found that the power FET had shorted don’t get excited and straight away replace the power FET and turn on the equipment. Chances is very high the new replacement of the power FET would blow again. Actually if you found a bad component in the power side (shorted FET), your next step would be to make sure all other corresponding components are good which include the primary winding of power transformer and also the secondary side diodes. If you have check all of the components then finally you can turn on the equipment but again please connect a light bulb in series with the mainline so that if there is still problem in the smps the components that you have replaced would not blow again due to the current have been limit by the light bulb

No Supply Voltage To Power IC

If you come across SMPS that have no supply voltage to the VCC pin of the Power IC, then there are four possible causes (assuming the fuse, bridge rectifier and filter capacitor are okay). The first one would be an open circuit in the start up resistor (high ohm resistor) that had prevented the voltage from going to the VCC pin of the power IC. The second one would be the VCC line circuit track open or dry joint . The third cause was Power IC shorted and the last cause was shorted corresponding components that are related to the Power IC. I came across a shorted ceramic capacitor (104 50 volt) that had pulled down the supply voltage.

If you need to isolate this problem, i guess the fastest would be by removing the Power IC and power on the equipment. For your information it will not blow the SMPS and after the removal of the Power IC and you get back the supply voltage, you can make the conclusion that it could be the Power IC had shorted or the corresponding components have problem. In certain cases you could also remove the switch mode transformer together with the Power IC and how’s the result like. Its on your preference because in troubleshooting and repairing SMPS there are many methods to isolate a fault. Test on the methods that can give you the most accurate result

What Voltages To Expect From The Secondary Output Of SMPS

Is the secondary output voltages important? Yes definitely, in fact all these output voltages are the testing point to check how well is the SMPS. That means by just placing your test probe on those output pins you would know if the SMPS is working good, bad or have intermittent problem. The question now is what if you have not repair that type of SMPS before? What are the voltages you should expect? Its easy, just look at the working voltage of the filter capacitors. If the filter capacitor is rated as 1000uF 25 VOLT then you can expect the output voltage somewhere from 14 to 18 volts. If you get about 5 to 6 volts then you know the SMPS is not producing the right voltage. The marking on the filter capacitors is a very good indicator of what output voltages that you should expect.


If you are repairing the Monitor SMPS, then surely you will know what output voltages to expect because CRT Monitors generally have a standard heater voltage which is 6.3 Volt DC. Not only that if you are checking the Boost circuit (that consist of B+ coil, B+ FET, B+ Diode, B+ Filter capacitor and current sense resistor) voltage line then you can expect about 45 to 50 VDC. If you get lesser than that say 25 volt, this clearly indicates the SMPS or the secondary side components that had caused the output to go low. This you have to troubleshoot and find it out with your troubleshooting skill.

Assuming you have not repair any Monitor (it can be other type of electronic equipment) before, what you need to do is to download the Monitor schematic diagrams and compares each of the SMPS output voltages so that you will roughly know what voltages a CRT Monitor can produce. Use this way to apply on other types of SMPS to locate the right output voltages.

Sometimes one have to spare some of their precious time to do their own research as with this way you will become independent faster than you can imagine. Without any sacrificial of your own time, you will only get slower result and this will overall affect your skill in electronic troubleshooting. Always think of a way that can help you to repair faster with accurate result either with the help of test equipments, coming out your own universal schematic diagram for a particular equipment or even from your own research and development (R & D). All the best to you

How To Locate The Primary Winding Of Flyback Transformer

Got a question from ERG member:

Can the Blue Ring Tester that I purchased from you be able to test the TV Flyback Transformers?

Jestine- Yes you can
And what If I do not have some of the TV schematic diagrams, how should I identify which pins in pair. Meaning to say pin No.? & pin No.? are related for testing.

Jestine- Check for the flyback pin that goes to the collector pin of HOT and the B+ pin (supply from power supply). That is the primary winding of flyback transformer.


If you are repairing the CRT Monitor then you have to find out from center pin of the B+ FET that goes through a Diode (ultra fast recovery diode) and then to the flyback pin. Another pin was from the collector of HOT. Both the pins is the primary winding of the flyback transformer. Try practice to find these two pins because i came across quite a number of technicians could not trace these pins. The primary winding is important if you are in the CRT TV/Monitor repair because a shorted/ partial shorted winding could cause the equipment to shutdown, low power, power blink or even blow up the HOT. If you come across a shorted HOT please make sure you test this primary winding before you put in a new HOT otherwise if the primary winding have problem, it may takes a split of seconds to kill the new HOT.

Again, it come back to the important of using flyback tester/Blue Ring Tester to find out the bad winding. Without the tester, surely it would take you a longer time to troubleshoot the problem that related to shorted primary winding in Flyback transformer

Understanding The TV Horizontal Output Stage

Here is a pdf file of how you can understand the TV horizontal output stage by Sencore. Click on the photo to check it out

Understanding The Operation Of A CRT Monitor

Here is a free note by National Semiconductor on How you can understand the operation of a CRT Monitor. Please click on the Monitor photo to view the pdf file. Make sure you have the adobe acrobat reader in your computer to read this file

Unstable Crystal Oscillator

Do you know that the crystal oscillator use in the electronic circuit board could become unstable or have problem when it gets hot? It could also cause intermittent problem and shutdown the function of microprocessor in electronic equipment. Problems like missing On screen display (OSD) in Monitor, intermittent appearance of the OSD, Computer motherboard “hang” and etc are just some of the problem cause by defective crystal.


As for the crystal problem when it gets hot, in fact you can use the hair blower to point at the crystal and observe the problem. Although we rarely replace crystal in electronic equipment, this doesn’t mean that you don’t need to check on the crystal. Get the same frequency value and replace and retest the set again. If you have the crystal tester or checker, then it would be easy for you to test out the crystal. In some digital meter, there are also a feature to test the crystal frequency while it is operating. If you get the exact frequency then you know the crystal is working fine and if the result is different from the value printed on the crystal body then get a replacement. The picture shown above is a 4 Mega hertz Crystal Oscillator

About UC3842 PWM IC

This UC3842 IC is one of the most famous PWM IC use in SMPS circuit. It can be found in many electronic equipment ranging from Monitor, TV up to computer power supply. Do you know that not all part number of UC3842 can be 100% substitute with another similar part number? Lets take this for example, you found the part number of SG THOMPSON UC3842 IC have problem and your supplier give you IP3842 while others give you HA17384 and Motorola UC3842.

Do you think that all these IC spec is the same? Not really until you have tested out on the equipment you repair. I came across Monitor produced hissing sound and power blink when different number used. After putting back the exact part number, all of these symptoms gone! Now not all equipment have the same problem-you just have to test it out yourself. Hope you can learn from my experience and if possible get back the same part number

TV And Monitor CRT Information

This fantastic website by Sam Goldwasser has helped me in many ways especially dealing with the picture tube (CRT). If you are in the CRT TV and Monitor repair field and haven’t read this article then you really have missed out some good information. The latest update for this article was 3 May 2008 and you can click on the picture to visit the website

Monitors That Had Been Touch By Someone Before

The chances of successful repair rate for an electronic equipment that had been repaired by inexperience technician before usually is not high. Why? Because many inexperience technicians sometimes do not know what they are doing. They made lots of error and if they can’t repair the set they would send to a professional repair shop or dealers hopefully the repair shop or the dealers could solve the problem for them. I don’t blame them for trying out and this is a fact i do came across quite a number of Monitors that had been touch up by someone before.

I really do not know who are they because i got the Monitors from our dealers and our dealers don’t repair Monitors. The thing that you don’t want to see the moment you open up the Monitor cover is MISSING COMPONENTS. If there is lot of components missing i will pack up the Monitor and return the set back to the dealers and will let the dealers about the problem hoping that they don’t receive such Monitors from the same customers again.

Besides components missing, sometimes you may encountered problem such as transistor installed the other way round, many big solder pad across the circuit board, solder bridge between components, loosen cables (degaussing and color cables out from the circuit), wrong part number especially on the diodes and transistors and etc. Normally we will not spend much time on such equipment because we know that the chances for us to repair the set was quite slim.

Recently there was a Monitor that had been repaired by someone and we found that the model have a common fault of IC problem. We found many solder joints problem and noticed that some of the joints have bridged over the other pins. We have cleaned the board but somehow the Monitor refuse to work-weird problem. We suspected that the person who repaired the Monitor may have shorted some other things in the circuit. Tracing back all of his previous job took us a lot of time and we decided not to repair it as we have more Monitors waiting for us to repair.

Well in this repair business we can’t always expect all equipment that come in for repair have not been repair by anyone before. You have to take note on which customers that always sent the equipment that have been repair before by someone so that you would not waste more time on such customers equipment. It’s just not worth it every time you have to waste more time to cover up other peoples inefficiency work