I tried to swap out the rectifier (D402) today and encountered a slew of troubles. In addition to the already burnt PCB through hole, I also managed to lift the plating around the other three leads when I was desoldering the old rectifier. This seems to be a fairly regular problem for me, so I'm wondering if there's a problem with my desoldering technique. (Iron too hot? Bad idea to use desoldering braid?)
![Undecided :-\](https://www.eevblog.com/forum/Smileys/default/undecided.gif.pagespeed.ce.cCZ6w-jWpR.gif)
After I thought I'd successfully bodged the new rectifier (NTE169) in, I powered the unit back on and discovered approximately no voltage on the +5V rail.
![Scared :scared:](https://www.eevblog.com/forum/Smileys/default/scared.gif.pagespeed.ce.oZptHNcbsD.gif)
I was quite worried at this point, so I shut the whole thing off and did another visual inspection of both sides.
Now I see at least three (new?) problems I'd previously missed: there is evidence of charring / melting of the enameled winding wire that connects to the black wire (19) on the transformer, one of the resistors (R339?) is burned, and C420 seems discolored (burned? you can see in my picture that one of the leads is an orange color). Also, the AC output points that go into the D402 rectifier are shorted (~0 Ohms).
I'm a little hesitant at this point to continue repairs ad-hoc for fear of further damaging the unit, so I think the next step is to carefully analyze the schematics and ask for more guidance.