If you are using the original type transistor, also check for high ESR
capacitors. You will need an ESR meter to find these, or change all the
caps to find it. The caps can also become a bit temperature sensitive.
--
Greetings,
Jerry Greenberg GLG Technologies GLG
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"Jeroni Paul" wrote in message
...
This set is chassis FL1.6, last summer a bad solder joint blew the PS
switching transistor, I repaired solder joint and replaced transistor 7216
(ON4827) by a BUT12AF. All fine until winter came, the set started to have
difficulties to start-up in a cold morning. It's been sitting since then and
now I'm trying to repair it. Using a hair drier to heat up the supply
section would fix the set and work fine until turned off and let it cool
down. When doesn't start, indicator 'on' comes, and after one minute
indicators 'mute', 'stereo' and 'st-by' flash (error 99, protection). No
power at all out of the supply, not any noise, nothing at all, just these
indicators on front panel.
B+ is 0V it should be 141V. All other outputs dead.
Okay, it took hours of work, but finally found the temperature sensitive
component is the switching transistor BUT12AF.
If I warm up it, then starts normally and works fine all the time. Any
mechanical stress has no effect and solder joints are fine. Could it be the
start-up base drive is too weak and so has difficulties to switch the
transistor when is cold?. Could it be the characteristics of original
transistor ON4827 were slightly different than the BUT12AF. Before I replace
that transistor again I would like to know if anyone has some experience
like that. Does some circuit need some tweaking after that replacement
transistor?
I'm really confused with this one, the BUT12AF transistor checks fine with a
diode tester and is almost new!! I tried disabling the MAIN SOPS and EHT
protection according to service manual with no difference.
Thank you and Merry Christmas.