Horiz output problem on a new phillips 32m800
Set squeels for a few seconds horiz derived voltages are 50% low after 10
sec picture comes on (scan derived voltages are about 80% now) and pic does not fill out the screen, Horiz output transister is getting hot a few more seconds and the set will go into shutdown. If you play with it enough (keep turning it on) the set will develop a full screen. Solution: replace 47Uf cap at the horiz driver transformer. The cap decouples the driver transformer from the transistor. IF it is low in value (weak) the drive signal is too low. After the cap warms up the set functions but the Horiz ouput transistor gets warmer than it should. This is an unusual design, took me a while to figure out. Most designs don't have a cap in the Horiz drive. The usual assumption is a bad flyback. Displays the classic symptoms; squeel, low scan voltages insufficient width and hot horiz out transistor but scope doesn't show the classic shorted turns ring. This problem will get worse over time until the problem will be easy to diagnose, as the horiz drive will disappear. |
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