Thursday, April 23, 2015

How to test Horizontal Output Transistor in circuit and out of circuit

One of my customers from Nigeria Mr.Kutelu send in this question to me this morning. for the purposes of those who could be having the same problem i have shared this...

Good day sir. Thanks for your help so far. Pls sir, how can I test Horizontal Output Transistor in circuit and out of circuit so as to know bad one?

Hi Kutelu
Kindly read your eBook page 52/53 for more info on this.

Basically when testing the HOT, first bear in mind all HOT transistors has B-C-E (1.2.3) leg distribution and therefore testing between C and E in circuit expect high and low…

This is because all HOT has in-built diode in them, HOT usually fail by shorting C-E junction and therefore if it is shorted you will find the reading is low both sides(same reading)

If this is the case just solder the transistor out of the circuit and test again between the middle leg(collector) and the emitter(leg on your right side if the transistor marking is facing you) and if you still get low and low(or two reading then the HOT is confirmed fault and should be replaced.

Kindly remember HOT does not just short, you have to find the cause which is making it to short and in most cases the cause is the snubber capacitor.

Other causes of HOT to short you can get more info in your eBook CRT television repair course Chapter 12: H.O.T getting shorted after replacement.

Bye and take care.

Regards Humphrey


  1. Thank you Sir.i learn again.

  2. TV no horizontal output but hot ok. What else could be the problem