Question about ViewSonic E70f 17" CRT Monitor

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Horizontal output transistor keeps failing

I have this 17" viewsonic and finally it fails, i check inside and found the horizontal output transistor BU4522AX fails, i've replaced it three times but keeps failing. dc voltages seems to be normal. please help me.

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Re: Horizontal output transistor keeps failing

The horizontal output transitor is always connected to the primary winding of the flyback transformer (via collector) and also to the horizontal deflection coil via an electrolytic capacitor. The most likely suspect for damaging the transistor is the fylback transformer. In some countries there are electronic stores that test flyback transformer by winding a few turns on the ferrite core and applying a test voltage. This test will only test the secondary. The primary winding is difficult to test for turn to turn short because the resistance is quite low and you do not know the 'good' resistance.

Posted on May 16, 2007

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Re: Horizontal output transistor keeps failing

What do u mean by LOT ( EHT ), in this problem, the main 200v supply intended for the horizontal output transistor wud passed thru a MOSFET, The gate was connected to the output of an IC that determines the presence of signal from a computer. The MOSFET would reduce this voltage to 165v for the hor transistor. now the presence of signal from computer would change the LED from orange to green, but the 200V did not passed to the hor transistor, the MOSFET was not turned on. One thing i've noticed was if i remove the hor out transistor, the MOSFET would turn on. This MOSFET will reduce the 200v to 165v so i could not try shorting it when the hor out transistor is soldered. i've already change shorted 0.22mf capacitor in the flyback transformer that i thought was the cause and the 2.2uf/50v capacitor blown before. please explain to me what u mean LOT.

Posted on May 20, 2007

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Re: Horizontal output transistor keeps failing

My tv is daewo 29 inch. help me what kind of horizontal out we are to replace cause its always damage in minutes.tyvm

Posted on Mar 10, 2009

Re: Horizontal output transistor keeps failing

Replaced your horizontal output transistor D5072 and this solve your problem.

Posted on Jan 28, 2008

Re: Horizontal output transistor keeps failing

Replace the LOT (eht) transformer and than put the new horizantal transistor than switch on and monitor will b displays ok

Posted on May 20, 2007

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Smps ok or no ehd

Check and replace damaged component/s at its horizontal scan output section circuit. Check the LOT (Line Output Transformer) too for damage. Replace the horizontal scan output transistor. Check the input voltage to LOT. If the voltage is absent check the feeder resistor; if any. If you wish to get some details; check the site linked here. Viewing it in "Mosaic" or "Magazine" will make surf easy. Surf the site with patience. Pull up older posts.
Do a search by type in the brand name of your device at its search box.

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Monitor no raster power has been ok


The screen is blank with no raster at all. There are indications that the channel numbers are changing in the display. This indicates that some of the low voltages are present but these may be derived from the standby supply.
Assuming there is no deflection and no High Voltage, you either have a low voltage power supply problem, bad start up circuit, or bad horizontal output transistor (HOT) or other bad parts in the horizontal deflection.

Check for bad fuses.

(If you have High Voltage as indicated by static electricity on the front of the screen and you hear the high pitched whine of the horizontal deflection when it is turned on, then the following does not apply).

Use an ohmmeter to test the HOT for shorts. If it is bad, look for open fusable resistors or other fuses you did not catch.
Assuming it is good, measure the voltage on the collector-emitter of the HOT (this is safe if there is no deflection). You should see the B+ - probably between 100 and 150 V.
If there is no voltage, you have a low voltage power supply problem and/or you have not found all the bad/open parts.
If there is voltage and no deflection (no high pitched whine and no HIGH VOLTAGE), you probably have a start up problem - all TVs need some kind of circuit to kick start the horizontal deflection until the auxiliary power outputs of the flyback are available. Some Zeniths use a simple multivibrator for this - a couple of transistors. Others power the horizontal osc. IC from a special line-derived voltage. The multivibrator type are sometimes designed to fail if someone keeps turning the set on and off (like kids playing) since the power rating is inadequate.
Test the transistors if it is that type with an ohmmeter. If one is shorted, you have a problem. The usual way a TV service person would test for start up problems is to inject a signal to the base of the HOT of about 15.75 kHz. If the TV then starts and runs once this signal is removed, the diagnosis is confirmed. This is risky - you can blow things up if not careful (including yourself).

If you hear the high pitched whine of the deflection and/or feel some static on the scree, confirm that the horizontal deflection and high voltage are working by adjusting the SCREEN control (probably on the flyback). If you can get a raster then your problem is probably in the video or chroma circuits, not the deflection or high voltage.

hope this helps......

Aug 06, 2010 | SAMTRON 77V 17" CRT Monitor

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this might be the problem of the disk capacitor of value 2kv, which is located at the horizontal section, i.e from the collector of horizontal output transistor.

Aug 04, 2010 | LG 700M 17" CRT Monitor

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a CRT monitor  just like a CRT television when it fails may still have a light on the front panel operate   you probably had a catastrophic failure  usually small electrolytic capacitors near the horizontal output transistor dry up an cause the transistor to fail  the voltage regulator may also fail in the process

Nov 07, 2009 | HP mx705 17" CRT Monitor

1 Answer


If you mean 'flyback' or 'horizontal output transformer' and have the part number available, try one of the sources here:
Flyback links 
If you do not have the number you may have to search Viewsonic's website to loacte it.
Warning; the number of suppliers for CRT monitor parts is shrinking rapidly, my best supplier, ICM in California is long gone. 

Mar 31, 2009 | ViewSonic E70f 17" CRT Monitor

1 Answer

Horizontal out always damage in minutes

Probable defective flyback (horizontal output transformer).  

Mar 10, 2009 | ViewSonic E70f 17" CRT Monitor

1 Answer

Sony videoscope xbr

the problem is most likely to be found on the HOrizontal Output Transistors note their numbers and replace them.this transistors are usually mounted on huge heatsinks.

Jul 05, 2008 | Mag Innovision InnoVision XJ 717 Monitor

1 Answer


this is definetly fault of EHT that big part in monitor replace it with original only duplicate or cheap may cause the problem adjust focuss control on EHT after fitting in on condition solder original transistor at h- output

Jun 04, 2008 | ViewSonic VX2235WM Monitor

1 Answer

Monitor makes annoying screech noise

What you are reporting is a problem in the horizontal section of your CRT monitor. Usually this is from a component that is failing in the Horizontal circuit.

Most CRT monitors use what is called scan rectification to develop the voltages required for the different circuits inside the monitor. This puts a strain on the Horizontal Output circuits that are responsible for not only the voltage to the flyback transformer to allow CRT illumination (40,000 or so volts DC), but some of the flyback secondary power circuits are what runs the rest of the monitor. When the components in the Horizontal output circuit get weak and can no longer support the higher demands of the dependant circuits, the flyback transformer tries to run harder. The more current it tries to draw to continue operating, the louder the whine becomes. Since the flyback operates around 17,000 cycles per second, it is in the audible range. Since you can physically hear it, you can also notice the change as the load demand on it changes.
What happens when you reduce the size of application windows or minimize them entirely is the demand on the power circuits is lessened and the flyback circuit is no longer trying to produce the higher demand that it was with the large application windows.

It is a good bet that it will not be too long before the Horizontal output and/or transformer give out completely and leave you with a dead monitor and a large repair bill.
Since it has not gone completely out yet, I would suggest you consult your local repair shop for an estimate. It may be a simple matter of replacing the high voltage capacitors around the Horizontal output transistor before the other parts in the horizontal circuit are damaged. This would certainly be a less expensive alternative.

If you opt to not get it repaired, new 17 inch LCD flat panel monitors can usually be purchased for around $150 or so.

Only you can decide which choice is right for you. At least now you have a few facts to help make the decision.

(I realize I probably gave you more information than you wanted, but I felt it might make things a bit easier to understand. If not, please forgive the disertation.)

I hope this helps.

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2 Answers

Horizontal scanning does not work

You have high voltage. Horizontal sweep is not working. Mostly we see shorted sweep transistor. Mike

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