Here is a small email I got from one of my CRT Television repair course customer.
Good day my friend,
i have a customer with Sanyo color 21" model AMV-2136 ...
Problem: Dead on arrival
Remedy: After opening the Equipment. Fuse is totally black (blown)
I replaced fuse, SOT and Ceramic caps across the base.
I power up using series bulb, still very bright
I de-solder 1 pin of all the primary components still bright light never goes off
I lift up center pin of SOT the bright bulb turns off (I remove again the SOT check with Multitester but its good)
I return the center pin. And lift the primary side of Chopper Xformer...the series bulb then goes off.
Inquiry: since i still not finished assembled my FBT tester because IC is not available on my town..maybe i go to nearby city to purchase the components of FBT tester.
my question is could it be possible that culprit is the chopper?
This is very intelligence investigations you have done Lito, Congratulations.
Let me add some conclusions from where you have said this: I lift up center pin of SOT the bright bulb turns off ( I remove again the SOT check with Multitester but its good)
Now the primary of the chopper transformer is basically from the Positive Pin of the Main Capacitor to the middle leg (Collector) of the Chopper transistor (S.O.T).
So it means if you remove the middle leg of the S.O.T you are actually left with the primary coil of the chopper transformer intact and therefore if the bulb lights went off this means the primary coil of the chopper transformer is not shorted and all the components from here backward are also ok..These components include the main capacitor, bridge diode, posistor and the small capacitors across the bridge diodes and therefore not considered for any further testing.
So now the problem could be Components which work together with the S.O.T, from my experience the biggest culprit is the transistor connected at the base of the S.O.T (like the famous C3807 which drive the S.O.T. next is Diodes and Ceramic capacitors around the primary side.
First I suggest you Change the S.O.T driver directly and if the short does not fade away, then take your digital meter and test across any capacitor on the primary side on the diode test scale and if you hear any beef then there is a shorted component on the line.
For further info please check out on this link
All the best Lito