DIYbanter - View Single Post - Samsung TXB-1930 TV not starting reiliably

lsmartino

ha escrito:

I replaced Q902 with an MJE2361 on a heat sink (it was the only NPN HV
power transistor my local electronics store had in stock) and also C970
and C974, as you recommended. That seems to have fixed it! Thank you.

This TV does not see much use, so there was a lot of blackening under
R901/R902/R903/R905 and none under Q602/Q603 (consistent with your
explanation). All of these resistors are still in spec, so I did not
replace them (even though I had purchased 5W replaceements). On my
chassis, R905 is 1.0K by measurement and by reading the color code.

The quality of your reply gave me the confidence to purchase the parts
before even opening the TV. Your analysis showed that you clearly
understood the circuit and the failure mechanism. From your
description, I could easily guess at a probable circuit diagram. Even
if I had had a circuit diagram, it would have taken serious
troubleshooting for me to isolate the problem. This is the first time
that I remember fixing a failure due to a partially degraded
semiconductor component. My most common failures are due to bad
electrolytics or completely zapped semis.

Again, thanks.

I´m glad to see that you solved the problem. I own a very similar TV
set with the same chassis as yours, and it gave me a lot of grief
before I understood how the standby circuit worked.