Laser 128ex....how to revive

[IlikeTech]

I would think that signal should be hotter? It's only 200mv Pk-Pk?

 

[OleLila]

Replaced C286 (not 266...schematic ink close together) 68pf......not sure if it is just the size of the cap or if I charge the cap by measuring, but it still looks like a short across the new cap.

Replaced Cap 127 between pin 14 of U26and gnd  because it looked burnt after I replaced U26

Replaced crystal XTAL1.

Still Nothing happening....same measurements with oscilloscope

 

[bibilit]

The only remaining clue is that short across the capacitor. 

Have you you still the short when the capacitor is removed ?

 

[OleLila]

no

 

[OleLila]

......and right on cue that's what I get for giving a definitive answer, I am measuring these but blew this one (maybe got it mixed up with the C127 change).....anyway, was going to take one more look at C286 this afternoon and just replace it and turn on, but when I took it off...yes there is a short across even when cap286 is removed ...anyway flipped the board over and thought I was going to be removing a solder bridge but it looks like its by design (see picture) 

 

[bibilit]

Pretty strange. I don’t see the point of bridging it and leaving a capacitor at the same time. 

Moreover solder is clean compared with the nearby ones. 

Another point, what about the inductor and the resistor behind U 26 ?

any way to isolate U26 from the rest of the circuit and see what’s going  on pin 8 ?

 

[OleLila]

This is after I removed capacitor and cleaned up with wick.

isolation is over and had to clean up for a while....will take the laser apart again hopefully in a couple of weeks and look at u26 as suggested and post follow up