You are right, the two vent holes are not present on 2002/2001 units. The most recent unit on this forum has TiN, mine one revision older. None of them has these external holes. Cover can be purchased from Tek for $50, If I remember it correctly.
The contamination on picture I will remove with plastic brush ( ESD) and compressed air. It is around AC circuit, so not so critical.
Did you power it up?
Thanks everyone with your responses so far. I am going to use the conservative route and do as little touching of the PCB as possible, relying instead on compressed air to get some of the dust out.
Certainly did power it up, yes. No voltage on any power rails on secondary side of T100. I annotated some measurements and voltages from the primary/secondary when I first applied power to the unit. So far here's what I've found as problems:
Optocoupler that drives the big power MOSFET in the primary pre-regulator circuit is totally blown - open circuit on the input LED. Testing S-D of Q101 for a short; no short present, good news, tested gate drive too; Q101 appears to be functional.
For the optocoupler replacement, I could find only the very similar TLP591B on Digikey. Same as the TLP590B except that it has a shunt resistor across the output pins "for optimized switching speed" according to the datasheet. Don't have much experience with opto replacements ... any idea if the TLP591B will work as a drop-in here? Was also considering a similar pinout but different topology opto like a transistor output opto but again, not certain this will work as a replacement.
On the digital board, I found a single diode short on rectifier CR622 ( red arrow points to the shorted diode ) CR624, CR625 tested good. Applied 7.5V to U619 and U629, received 5V out. Appear to be good, I will replace anyway just to be safe. Could not test comparators U627, U628, U629 yet. Obviously all caps on the + output of CR622 I'm going to replace as a matter of course. Also will probably replace Q608 which might have destroyed the opto's input.
My guess at what happened is probably a voltage spike on the lines coming in from J1032 caused the rectifier CR622 to blow, also perhaps sending the spike further down the line on the +5VC rail and blowing the opto.