Customer support-via email part 2 between me and Bogie from Philippines

Good day Sir, I have read the post on your blog spot and so amazed about  your explanation with regard to that IC1751. 2 hands up, you’re really a good teacher.

Thank you and welcome Bogie.

Actually, i did not know that IC1751 was a RGB driver IC because  as repair to your book the RGB IC there was only 15 pins and that IC 1751 has a 30 pins and its mounted on main board. Anyway Sir how did you know that IC1751 was a RGB driver ic? where did you get the info? Is there any website to learn it?

I don’t know where you get a RGB driver ic with 15 pins in my book, I have given an example of TDA 6107Q on chapter 11 (understanding the fly back transformer) which I also encourage you to look at it for more info. on the issue before you.

On the IC1751…I got the info from the pdf file you send me page 31. Again from the datasheet I see it has 9 pins unless if you referred to a different I.C.

Sir I have another TV here which I bought in a junk shop Sanyo 14 inch. AS i open the unit the fuse was ok and I apply the series bulb, the bulb lit for a second then turn off so it means the primary side of PSU was ok?

Means primary side has no Short but does not mean it has no problem…so it could be having a problem but not shorted.

Checking the B+ it has 114v and at RGB cathode pins all 3 has a 114v also. No voltage reading on G2 and Heater. TV screen still don't have any appearance.

This means that the power supply is working because there is output on the secondary side (most importantly the B+ supply which is the main supply for the secondary side.

The 114v at RGB cathode pins all 3 means that the fly back is not working otherwise this voltage could have been around 180 volts.

So I would advise you to check the drive circuit of this TV, see chap10 (understanding the horizontal circuit) in your book.

Most important here is to check if there is voltage at the collector pin of the horizontal drive transistor, is there around 0.6 volts at the base of the drive transistor? Check for dry joints around the driver transformer too. Is the horizontal vcc present on the main ic(H-Vcc is usually 9 volts) so check out for any 9 Volts regulator and see if it has any output.

Testing voltages on vertical Ic which have 7 pins i got only 2.28v at pin 2 and 4.28v at pin 3. Desolder the vertical IC, i still got the same reading.

For the vertical ic, most important is to check if there is voltage at the Vcc pin, again most vertical ic get there voltage from the flyback and this confirm to us that the flyback in not getting excited. So for now let us concentrate on the flyback.

Testing the diode secondary side of the PSU which suppose will give me 24v, it has only 22v and even on the filter caps rated 35v it has also have 22v. What will be my next move here Sir?

This is ok Bogie, this voltage is not fixed and therefore it can vary and this is normal

Did the primary side of PSU still have a problem?

For now I can’t see any cause for alarm on the PSU. Concentrate on the horizontal drive and horizontal output.

Thank you very much Sir and GOD bless...Bogie

Most welcome Bogie.

Humphrey