Continuous troubleshooting reveals differences in the schematic vs the board. Finally brute forced a solution.
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https://www.youtube.com/watch?v=yqSm6XbWte0
Thermal shut-down is typically caused by blockage of the heat exchanger. true of this scenario. not enough air flow causes overheating.
Here's how to disassemble and clean the heat exchanger.
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https://www.youtube.com/watch?v=0TtBJK3z0So
Now reassembled, its time to make the final tweaks to the set before putting it through s long burn-in phase. This is 8 hours a day for 5 days. Observing changes or strange behaviors. Once complete it will head home to its owner.
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https://www.youtube.com/watch?v=qZfIZQD7dg0
Noisy when tuning? Can't tune, or lock a station? Your tuning capacitor may be oxidized. Here's a brief tutorial on cleaning
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https://www.youtube.com/watch?v=RbjwiggmnrQ
Replacing the STK power pack with the Yuan-Jing TDA 7293 modules available through parts express. Most modern STK manufacturing is crummy, so if you're tired of the receiver blowing up, give this a try. Outputs the same power, perhaps a smidgen less gain.
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https://www.youtube.com/watch?v=7uqEk4qAYKU