Blazing hot U4!

[hopelessennui]

I powered up my j99 to test the voltages for the op amps and i started to smell something, when i touched the heat sink on the U4 it burnt my finger! i quckly turned it off. after it cooled down i turned it on again and within 10 seconds the U4 was hot enough so that i could not touch it.

The power regulators U4 and U5 are not switched (U5 by the way is nice and cool), it is not backwards, there are no solder bridges. any ideas on what would cause this intense heat so quickly?

visually U4 looks fine it didnt start burning, is there a possibilty its still good?

[hopelessennui]

ok, cap c20 was on backwards. works good now.