Question about Fisher RS909
Well now you did most of what would be recomended. Try this, When the unit trips into protect, check on the output pin on the output IC or if its a transistor output the speaker output BEFORE the protect relay.. If theres any DC voltage on the output pin then you know the problems in that IC or output circuit. If its a transistor type output, I would suspect the differenal circuit. Way up near the input circuit. Its two transistors back to back. They may check good on a regular check so do a high resistive check And see if theres any type of leakage. These I have seen many many times in a Sanyo/Fisher Stereo system to be the problem. If its an IC output, try disconecting that side of the bad output and see if the unit works ok. If theres no DC voltage on the speaker output pins BEFORE the saftey relay then I would suspect the protection circuits bad. Theres op amps in these circuits that are used as comparators and they do go bad. You dont want to dig this deep and get a service diagram, and the units over several years old TOSS it and upgrade!! Good Luck
Posted on Aug 05, 2006
Tips for a great answer:
It could be a problem of cold solder joints, or solder joints
on the main board which have cracked over time due to thermal expansion and contraction
of the circuit board. Repair is to find and reflow the cracked joints. You may
want to consider hiring the services of a reputable repair professional to deal
with getting your set back into normal operating condition.
However TV's attempt to protect themselves from damage by
shutting down. Your unit has three main ways to protect from damage.
The TV monitors various DC voltage supplies. If one of the
supplies is missing. The TV shuts off.
The TV monitors excessive high voltage and beam current. When
the TV detects that one of these is too high the TV shuts off.
OVER CURRENT PROTECTION
This will activate if excessive current drain on the 130 volt
supply line. If the TV detects this supply line is too high the TV shuts off.
Most units made in 1999 have a diagnostic mode to help
determine the cause.
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