No vertical in crt tv(Need Help)

[dark phobia]

i have a old sony trinitron k21t3d tv. Problem is no vertical picture. when i turn on the tv 1 inch horizontal line appears.
Vertical deflection has two part one is tda8139 and other one is stv9379.
i checked the voltages tda8139 and voltages are good.
but ic501 stv9379(vertical deflection booster) have no voltage.
T802 is flyback transformer i measure voltage at 10th (24v ac) . No dc voltage. is it normal? because this voltage goes to ic501(stv9379 second leg) and not working.
Should i change stv9379?
Could you please help?





http://diagramas.diagramasde.com/televisores/KV-21M3A_T_M3B_T3B_M3D_M3E_T3E_M3K_T3K_M3L_T3L_T3R_M3U_T3U Ch.BE-4A.pdf

 

[KrisBlueNZ]

Hi there and welcome to Electronics Point

I wouldn't take too much notice of the voltage you measure on pin 10 of the flyback transformer. This voltage is not a sinewave, so a standard multimeter (that doesn't have true RMS capability) will not measure it correctly.

IC501, the STV9379, is the vertical output stage that drives the deflection yoke. If it doesn't have supply voltage, obviously it won't work. So you should first check R814 the fusible resistor. If it has fused, you can replace it, but it's quite possible that IC501 has failed, in which case the replacement R814 will fuse again.

Also check C820 for bulging, and with a capacitance meter if you have one, or just replace it on suspicion.

 

[dark phobia]

Hi Kris thankyou for wellcome and help.

My mind is confused with voltage on pin 10 of the flyback. You are saying that is normal so we have another problem than.
I have dmm with lcr and not measure more than 200mf. I connected serial small one capacitor to big capacitor and measuring this way. Yesterday i soldered out c820 and checked. İts seem to me fine.
R814 is normal resistor. and checked is too also fine.
Today i ordering stv9379 and some other parts. I will change ic501, r814 and c820. I wish thats the solution.

 

[KrisBlueNZ]

I'm not saying it's normal; I'm saying that you can't tell for sure.

If you're sure that the 28V rail at IC501 is not present, I think replacing those parts will probably fix the problem. D806 could also be faulty and would be worth replacing "on suspicion" as well.

Good luck!

 

[dark phobia]

ok my friend. Thankyou for fast reply.

D806(rgp10g) not found in my area can i use ba157 instead of rgp10g.

http://www.vishay.com/docs/88536/ba157.pdf

http://www.vishay.com/docs/88700/rgp10a.pdf

thankyou.

 

[KrisBlueNZ]

Yes; they look to be the same!

 

[dark phobia]

Problem solved . I changed R814 and thats it. Tv working now. Thanks for help.

 

[KrisBlueNZ]

Cool