Midway 80-901 2N2905a goes nuclear

[MrSinister]

Rebuilt the linear power supply in a gunfight its a 80-901. It's the earlier version with the edge connector. The LM305AH was shorted. Replaced it and voltage is perfect, but after a few minutes the 2N2905A goes nuclear hot. I've checked everything on the circuit and didn't find any shorts. It's weird that the voltage is rock solid while the 2N2905A gets insanely hot.

What would cause this? I replaced the disc capacitors with no change.

 

[cwilkson]

Discs caps are unlikely to fail unless they are physically damaged. Most often this shows up as broken leads.
But not likely at fault here.

If the 2n3055 fails open then the 2n2905A will have to supply the entire +5V current. It will likely melt.
So check the 2n3055 out of circuit. If you have to replace it only buy from trusted sources: Digikey, Mouser, APAR.

If the 2n2905A has been nuclear, I would replace it too. Just to be sure. Same rules. Buy it from one of the above sources.

 

[MrSinister]

Apar. I'll pull it later this week and test. I replaced it with the rebuild kit from apar already. The disc cap nearest 2905a tested shorted in circuit. I replaced the LM305 and short was gone.

 

[MrSinister]

2n3055 tested good but I replaced it anyway along with the 2n2905a again. So far so good. Not sure what the issue was. I replaced them all with the kit from peter to begin with.

 

[cwilkson]

Glad it's working!

Is the 2n3055 soldered or socketed?
A bad joint or weak socket could cause it to appear open in the circuit.

 

[MrSinister]

Soldered. I reflowed the resistors also from the 2n3055. Thanks for the help