Why Horizontal Output Transistor In CRT Monitor Get Shorted?
There are many reasons why the horizontal output transistor (HOT) shorted in CRT Monitor. Here are the possible cause:
HOT have life span-it can work for many years but out of a sudden it can just go shorted. Replacing only the HOT solved the probem!
Dry joints in nearby area- Yes, dry joints in the HOT leads, flyback transformer, horizontal driver circuits could cause HOT to blow.
Shorted flyback primary winding. I came across lots of HOT failure due to shorted primary winding in flyback transformer. One of the best example was the HP 17″ 7500 CRT Monitor. Not only it blow the HOT, the B+ coil and the B+ FET blown as well!
Shorted or open internal capacitor in flyback transformer. These problems has contributed lots of HOT failure in CRT Monitor. Normally i will check the internal capacitor first before i replace the HOT and switch “ON” the Monitor.
Too high B+ voltage- A higher than normal B+ voltage will kill the HOT instantly. Make sure the B+ is supplying the right voltage to the primary winding of flyback transformer.
Running at wrong frequency- I once came across the horizontal driver circuit area was running at different frequency. It suppose to run on a 31.5 Khz (depends on resolution in your CPU setting) but this faulty Monitor run at a too low frequency killing the HOT after “ON” for few hours!
Bad electrolytic capacitor in the supply line to horizontal driver transformer- If you found a HOT shorted make sure you check on this capacitor otherwise you may get a call back from your customer saying the Monitor not working again. The capacitor usually developed high ESR value that destroy the HOT in few hours to few weeks time.
Shorted horizontal yoke coils- A shorted horizontal yoke coil could instantly kill the HOT. I always use the dick smith flyback tester to confirm first that the yoke coil is good before the replacement of a new HOT.
Safety capacitor value out- If this safety (holddown) capacitor value dropped to zero, the high voltage produced at the anode could shoot up to over 30 kilo volt thus killing the HOT in a split of seconds.
Wrong replacement-The Monitor could be repaired by someone else and they had fitted a different specification of HOT thus making the HOT won’t perform the best and breakdown after certain of time.
Nearby components- There are some possibilities too that the bad components nearby the HOT could cause the HOT to blow. Check the surrounding components before you switch “On” the Monitor.
Well, hope you can absorb these tips and start repairing CRT Monitor or TV with more confident! Have a brilliant day!
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admin
July 12, 2010 at 4:23 am
Hi jeoffrey,
The B+ voltage must reach to the flyback primary winding and at the same time the HOT base pin must have waveform.
Jestine
Mr.Gondo
July 12, 2010 at 8:29 am
sukses selalu mr.justine,
terimakasih untuk semua informasi pada website anda.
saya mau menanyakan persamaan untuk Flyback monitor sampo FEA 924 ( BH26-00072A ).
Terima Kasih banyak atas atensinya.
gondo.
admin
July 13, 2010 at 9:43 am
HI Gondo,
Terima kasih tetapi saya tiada maklumat tentang persamaan flyback tersebut.
Jestine
RGALEJA
July 16, 2010 at 9:07 am
Hi Justine,
I have CTX Monitor I was plugging it to 264Volts and suddenly fume. I look at power supply I found the resistor was burned. But I don’t know the value; even color code had been burned. Only the schematic diagram number is there R901 R802 may I Know how to find equivalent of these resistor.
Thank you.
admin
July 16, 2010 at 7:51 pm
HI Rgaleja,
If there is no info then it would be very tough. I suggest that you find a near similar model of the monitor diagram and look out for the resistor value. For example if your CTX monitor model is CTX1567 then look for anything like CTX1585, CTX1598 and etc. Sometimes they may have some similarity in design of the pcb board and you can use that for finding out the resistor value.
Jestine
paine
July 28, 2010 at 11:29 am
dear jestine,
i am verry weak in english so pointing out problem shortly
lg500g
SAA4849p is used in the circuit
1) power supply is ok all voltage out properly
2) j6810 was heating not shorted
3) fly back transformer is ok i checked it with other set.
4) fly back generates for 2 second and gets off simultaniously.
5) i checked HFB and XRAY protection circuit for faulty component but not found anything.
6) i replaced all electrolyte capacitor of power output section with there proper value.
with thanks
admin
July 29, 2010 at 8:56 am
HI Paine,
Have you check the B+ voltage? If it too high it can cause the high voltage to shut down. Please visit this link to check the internal capacitor:
http://www.electronicrepairguide.com/testing-flyback-transformer.html
Jestine
Raja Wahlang
August 2, 2010 at 3:46 am
Hi Justine,
I have a problem with my LG Flatron T710SH 17" CRT Monitor. The MOSFET 10N20C overheat and blows off but the HOT J5804 remain intact. So i thought the EHT must have gone, so i replaced with a new one with the same pin configuration and serial number. After replacement the MOSFET blows again. I have checked the sourounding components but couldnt fine the fault. Please tell me where can the fault be.
admin
August 2, 2010 at 5:29 am
Hi Raja,
If the mosfet is the B+ fet then you can try remove it and power on the monitor. I'm afraid the gate signal to the fet that cause the fet to blow. Try visit this link to check if the B+ line voltage is too high or not:
http://www.scribd.com/doc/2957819/TT204-Identifying-television-SMPS-problems
Jestine
harry
August 26, 2010 at 7:25 am
I have Gtc 17"CPU monitor acting weird, it won't start(blank),but if I shake it or take of the back cover it will start. I think maybe some soldering get losen, I have tried to locate it until now I can find it. Any solution? (It will go blank too if I change the resolution or the refresh rate).
admin
August 26, 2010 at 7:39 pm
HI Harry,
Try check these section for dry joints: CPU and EEprom ic, flyback transformer pin and the CRT socket pins in the CRT board. You can try gently knock on the Monitor board with the handle of the screw driver.
Jestine
Harry
August 27, 2010 at 3:24 am
Mr. Jestine,
Is it okay if I spray the CRT socket pin with contact cleaner?
thanks.
admin
August 27, 2010 at 9:44 am
HI Harry,
Yes you can spray it. If the problem still persist, just direct replace the socket.
Jestine
Paula
August 27, 2010 at 11:36 am
Thanks....but I thought you could be more specific to model# 27u-s60 Sharp....the hot blows out after a second the set is turned on...could this be the flyback back or capacitor in the high voltage...
admin
August 27, 2010 at 9:28 pm
HI PAULA,
I wish i can tell you the direct answer but sorry i can't be specific because in the market there are thousands of Tv model. This article are the possible causes of why HOT burnt. Yout TV problem can be in one of the list. I guess you may need to check it out accordingly as throughout this finding process you will learn along the way. So next time, whenever a TV/Monitor have the same symptom, you will know what to do and how to troubleshoot it.
Jestine
harry
August 28, 2010 at 6:31 am
Jestine,
Problem solved, it's the dry joints on diodes from the power supply.
But new problem occur, at the bottom of the screen ,flicker horizontal lines appear: http://yfrog.com/n0mymonitorj
gradually turn to normal in minutes, dry caps maybe?,
Which part should I try to locate the trouble?
admin
August 28, 2010 at 9:24 am
Hi Harry,
You need to check on the vertical section. Direct replace the e-caps or the vertical ic and retest.
Jestine
hasan
September 17, 2010 at 3:11 pm
you are the the best it remind me of sony 21inches flat screen iwas repairing i replace c 5855 twice they blew in second the third time after reading your news later yes icheck the component around and found another small transister blown i replace them yes is done THANKS J.Y
admin
September 17, 2010 at 7:21 pm
HI Hasan,
You are welcome.
Jestine
hanux
September 20, 2010 at 2:46 am
Hi Jestine
i had 17" Viewsonic monitor,
sometime my screen goes blank but the indicator's still on, after i turn off the power and turn it on, picture back to normal again, but sometime it goes blank again. is it the HOT or Flyback broken?
thank you
admin
September 20, 2010 at 5:01 am
HI Hanux,
When it goes blank, is there G2 voltage in the crt board? If no G2 voltage then the flyback is not energizing. This most probably missing either the B+ voltage or the signal to HOT. If there is G2 voltage then make sure is about 250 to 300 vdc and the heater is supplying 6.3 vdc to the crt board.
Jestine
henry
September 21, 2010 at 11:23 pm
these would be helpful mr. Yong
leonard williams
September 30, 2010 at 9:30 am
hello please if you could tell me how to get into the service moode of this RCA tv model RN-21EO9 thanks in advanse
Daniel
September 30, 2010 at 11:19 pm
Dear Jestine Sir,
I have one problem in some chinese moniter is use in which Samsung 17" CRT Moniter PCB is used in which one porblem comes some time we face EHT not started all voltage comes even HOT get voltage also. In which Horizontal Occilator is TDA4859PS is used we don't have proper circuit so we unable to find EHT start voltage pin in that IC Please guide us sir for finding that fault so that we can able to repair that fault.
admin
October 1, 2010 at 2:05 am
HI Leonard,
Sorry no info on this.
Jestine
admin
October 1, 2010 at 2:15 am
HI Daniel,
What is the complaint of this monitor? Is there B+ supply voltage to flyback transformer? Is there a squarewave measure at the base pin of HOT?
Jestine
leonard williams
October 14, 2010 at 8:13 pm
hello mr young please help me to get into the service mood of RCA tv model RN-21EO9 i would be thank full your turly leonard'
admin
October 14, 2010 at 9:26 pm
HI Leonard,
Sorry i have no info on this.
Jestine
ruben caro
October 18, 2010 at 12:56 pm
Panasonic Model# CT36HX42F. I have a problem with the tv. The Tv always worked fine and all of a sudden it quit working, when you press the power button the red LED will turn on and you here 3 clicking noise and it immediately shuts off, i press the power button again and absolutely nothing happens, i unplug the tv and replug it and thats when i press the power button and it does the 3 clicking noise again and the same outcome. i had the TV off for 4 months and then TV worked all of a sudden. the tv was working perfectly for about a week and now it just quit all over again and it has the same problem. can you please give me a solution to the problem or where i can get the solution so i can fix it myself. most appreciated thanks
Seltan
October 19, 2010 at 3:08 am
Hi Jestine,
Thanks for the unvaluable technics that you teach us.
We have 10 Daewoo 719B monitors and they all failed with in a limited period of time. The HOT transistor fails even after replacement. I have tried to diagnose most of them but couldn't find the problem. Is there a time bomb in the monitor? Please help me solve this problem.
Thanks,
Seltan from Eritrea, Africa
admin
October 20, 2010 at 4:49 am
HI Seltan,
There is no time bomb in crt monitors. Have you check according to the suggestion that i have listed above? There must be a reason why the HOT shorted.
Jestine
admin
October 20, 2010 at 7:47 am
HI Ruben,
It could have dry joints problem in the power primary side. You may also need to check if there are any bad filter capacitors in the secondary output side. Always make sure the output voltages from the SMPS are good and stable.
Jestine
leonard williams
November 14, 2010 at 3:46 pm
my lcd tv is showing dark even when i turn up the back light the model is 37lg30-ud'
admin
November 15, 2010 at 9:22 pm
Hi Leonard,
Have you check to see if there is any dc supply voltage to the inverter ICs?
Jestine
Anand
November 21, 2010 at 2:07 am
This is a very useful information. I recently faced this problem. The CRT monitor's Transformer (LOT, as it is locally know) was either shorted or blown. The technician replaced the Transformer along with the Transistor, saying this is a common occurrance in CRT monitors after a few years of operation. Mine worked without problems for more than 9 years before this problem occurred.Thanks.
admin
November 22, 2010 at 10:59 am
HI Anand,
Once you replace with an original part number and check for dry joints then the Monitor should be working fine.
Jestine
baidya
November 23, 2010 at 2:20 pm
hi sir plese tell me the reason of fluctuate supply from smps. i mean rapid up n down voltage on multimeter, specialy a 3842 ic based smps,
admin
November 24, 2010 at 11:04 am
HI Baidya,
It can be cause by component shorted in the secondary side or the primary side area itself have problem such as bad power ic, resistor turn into high ohm , bad filter cap and even leaky diode or transistor. You may need to isolate the problem using this link below:
http://www.scribd.com/doc/2957819/TT204-Identifying-television-SMPS-problems
Jestine
mathesh
November 26, 2010 at 3:36 am
my problem is HP 15" Monitor was not working smps section ok. when cpu is switched on the monitor green LED Flowing but not display the screen only black screen display. please give some tip to solve this problem
admin
November 29, 2010 at 8:46 pm
HI Mathesh,
You need to make sure the B+ voltage is reaching the flyback and the HOT base pin have a pulse from the horizontal/vertical oscillator ic.
Jestine
Raja Wahlang
December 30, 2010 at 11:32 am
The FET at +B blows off. I have replaced it with a new one, but still continues to go off. I have checked the ceremic capacitor of flyback transformer filtering 400v, its ok. I have even replaced the HOT with the same specification. so what can be the cause of the FET(B+) at primary section of HOT to blow off every time. Please reply...
admin
December 30, 2010 at 10:39 pm
Hi Raja,
Check for shorted B+ coil or even shorted primary winding in the flyback transformer with Blue Ring Tester. Make sure also the incoming supply voltage to the B+ fet is not too high.
Jestine
Mathesh
January 1, 2011 at 1:55 am
hello Sir,
my problem is 15"& 17" IBM CRT monitor No picture, power led blinking, ticking sound Continuously please reply sir
admin
January 1, 2011 at 11:53 pm
HI Mathesh,
I suggest that you visit this website to isolate the problem :
http://www.scribd.com/doc/2957819/TT204-Identifying-television-SMPS-problems
Jestine
hirwadun (dun)
January 4, 2011 at 2:02 pm
Dear Jestine
tv philips 29inch...transistor(bu 2508dx) blow after changed..is't problem with their fbt or dy...can we change it's with not original fbt or dy
admin
January 4, 2011 at 10:35 pm
HI Dun,
The best is to replace with the original fbt and dy. If the flyback or dy spec is different, the display will be affected and blow the HOT too.
Jestine
mathankumar
January 7, 2011 at 12:57 am
hello sir,
my problem is CRT 17" Monitor No picture, power led blinking, HOT section OK. please sir give me some information on how to identify the faulty components
admin
January 7, 2011 at 5:03 am
HI Mathan,
Try isolate the problem using this link:
http://www.scribd.com/doc/2957819/TT204-Identifying-television-SMPS-problems
Jestine
mathankumar
January 11, 2011 at 3:17 am
hello Sir
i need Electronics repair and service book & Monitor repair and service books please send the details about the book price and address sir
admin
January 11, 2011 at 6:24 am
HI Mathan,
I have the LCD Monitor repair ebook and do not have crt monitor repair ebook. You can access the website at http://www.lcd-monitor-repair.com
Jestine