No power without heating logic board
I have seen a number of posts concerning "no power issues" here and some other websites but nothing fits the problem my Mac is facing.
I have a MacBook Pro "Core 2 Duo" 2.8 15" (late 2008), which is running without any errors unless I switch it off and want to start it again. It simply doesn't start unless I heat the logic board (e.g. with a hair dryer). It is really weird, because it is running for month without any error indications unless it is switched off. It shows no activity, apart from the LED of the battery and the MagSafe charger indicating charing and a fully charged battery. I tried the following to find the error:
Checked power supply: I have a working battery (only 16 cycles fully charged. I use the 85 W Magesafe adapter. LEDs behave normal indicating a fully charged state.
I reset SMC and PRAM several time, no effects.
I removed the battery in the power cord, pressed the on button for 10 sec, connected the power cord while holding the power button another 10 sec and tried to start, but no response.
I tried to start the Mac directly on the logic board after disconnecting the flatband cable of the keyboard but no response.
The only way I can start the Mac is to heat the logic board with a normal hairdryer, for about 1-2 min. For me this indicates a bad contact somewhere which gets fixed by the thermal expansion upon heating.
However, it appears weird that the Mac does't fails when it is cooled down again. So I checked all the temperature sensors (they are all working) and the Mac does't fail even the temperature is dropping below 20°C at the CPU. I really actively cooled the Mac while in sleep mode by putting it outside on the balcony (6°C) and still no failure. Because it doesn't fail upon cooling it appears unlikely to be a problem with a solder point directly on the CPU.
I thought maybe it is just a bad cable somewhere, but I don't know which cable could hinder the start-up but not affect anything else.
I have really no idea how I could further localize the problem or solve this error.
Please help me if anyone has an idea, what could cause this problem.
Is this a good question?