Atari 400 power on successfully only now and then

[+Spancho]

9 hours ago, BillC said:

The regulator isn't outputting 13V, the voltage is coming through the 33 ohm resistor, without any current there is no voltage drop across it which is why I suggested a load test.

 

The resistor should deliver about 240mA current over what the regulator can supply,(13V-5V)/33 ohm, as longer as the load requires more current than this the voltage should be properly regulated.

I am not into electronics, so my idea to deal with that would be to replace the 7805 with a 1,5A rated one and taking out the resistor.

[BillC]

11 hours ago, Spancho said:

I am not into electronics, so my idea to deal with that would be to replace the 7805 with a 1,5A rated one and taking out the resistor.

It could be that at the time higher rated 7805 were significantly more expensive, the 400/800 were designed in the late 70's after all, the 33 ohm resistor adds additional current for pennies and voltage regulation is still maintained as longer as there is sufficient current demand. 

 

Why go to the trouble/expense of replacing the 7805/removing the resistor?

Under sufficient load the voltage can't go high unless the 7805 fails, if the 7805 fails the damage should be the same with/without the 33 ohm resistor.