Fuse, I'm pretty sure--always, when in doubt consider the place in the circuitry. From what I can see, this looks like it's bridging a connector pin with a trace. That would make it a fuse.
The PSU schematic
PDF page 26 would seem to verify this.
Crikey, that diagram is difficult to read! Of course, the only page that's hard to read is the one I need.
Any chance someone has a clearer shot of this page? The only fuse I can see in the component list is PF27 at the top, and that's an actual glass fuse at the AC power switch. This component is on the secondary side of the PSU at the +12V output to the video adapter/CRT. Better context shown here. (Also looks like a made a nice scratch on the PCB. Naughty me.)
Is there another fuse besides this one that you can see? Schematics are not my strong suit. I'm a trace and replace kind of guy. ;-)
Big picture, I'm dealing with a dead PSU. Not confident this fuse is the root cause, but clearly needs fixed. It's possible I cracked this while desoldering as part of my troubleshooting. I guess I could place a 35K resistor there temporarily to verify that?
Incidentally, I got this PC6300 at the CR warehouse last month where it powered up all the way to ask for a system disk. Second boot attempt, I didn't realize the power switch was in the ON position before plugging in the power cord. And now...only the case fan runs. No pops or smoke. That's where it sits right now. When I put an ohm meter on the 12V and 5V PSU outputs, both are shorted. I've confirmed the first stage is producing 160V DC at the rectifier bridge capacitors that feed the secondary, and that board doesn't show any shorts (the PSU is split into 2 boards). I've also verified the secondary board is sending back nil reference voltage to the first stage, hence no PSU output. I've poked around for quite some time, but can't seem to find the short. All of the caps are electrolytic (no tantalums). Most seem to check out fine in circuit, and I've removed a few other smaller ones that check out fine. That leaves a few larger caps, but I'm not accustomed to electrolytics causing shorts, because unlike tantalums their ESR usually increases as they go bad. Still working my way through diodes, a handful of mosfets, and a set of transistors. Things that won't test in circuit, I'm having to remove to test which worries me that I'll damage something (else).
All suggestions are sincerely appreciated!
