Atari 800 NTSC Hardware heat, help needed : )

[Cambouis de l'Atari]

Hello,

Last time I plugged my 800, I smelled a nasty smoke... it was still working but I switched it off quickly.

I opened it, and located the source of heat : a resistor.

 

 

I also noticed that one of the 4700µF capacitors was puffy.

 

So I ordered 2 capas and replaced them.

But that resistor is still getting very hot when powered...

 

Edit : there is 7.80v on that resistor.

 

 

Any idea someone ?

 

Thanks for reading !

 

Edited June 30, 2021 by Cambouis de l'Atari

[TGB1718]

If that's R203 it's a 33 Ohm 2 Watt resistor, so with 7.8V across it, it will be dissipating about 1.8 Watts so it will be hot.

 

Have you measured the voltages +5A,+5B,-5 and +12 to make sure they are at the correct levels.

 

Edit: I found the board layout and that is R203, lower far left of this diagram.

 

Edited June 30, 2021 by TGB1718
Update

[Cambouis de l'Atari]

Yes it's the R203.

 

Do you mean that the heat at the resistor is normal, the smoke just coming from the capacitor ?

Or that 7.80v is too much and we should expect 5v ? If someone can confirm ?

 

I'm sorry, I'm not used to the 800 board. Top voltage regulator seems ok. Could someone show me some points where to check the voltage ? Or point me to some ressources on 800 failure trackings ?

 

Edited July 1, 2021 by Cambouis de l'Atari
accidental posting

[TGB1718]

Here's the circuit diagram, find the junctions of the components "ringed" and measure the voltage with respect

to 0V, the 7.8V across the resistor is not the voltage present at the 5V line.

 

It is normal for that resistor to get hot, as you say the problem was with failed capacitors.

 

 

[Cambouis de l'Atari]

Ok everything is fine ! That resistor is indeed hot, but far less than when the capacitor died !

Thanks for your help : )