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As someone who doesn't own an AIO: do the speakers on these plug into a header on the motherboard like the G3 desktop/tower, or do they connect somewhere else (as in, somewhere on the analog board perhaps)? Personally I'd start by powering it on and once it starts acting up, pull out the...

Only way I can imagine that resistor blowing up is if it was already damaged; it should never have enough of a voltage drop across it to cause that in this circuit. As an aside, I think that Q9 in the schematic might have its base and collector pins reversed mistakenly. Don't have an Apple ///...

If I'm reading crazyfrog's post correctly it sounds like installing the termination resistor packs on their BlueSCSI solved the gray screen problem. Might be something you want to double-check on yours...

For the time being, I think you're right for not pulling the legs out of the board. If the resistors don't want to come up it's because the through-holes haven't been entirely cleared of solder (the resistors aren't glued), and forcing them up would damage the board. The bandwidth of your old...

The +5V rail you measure at any one point on the board is the same +5V you'll read at any other point, same with ground, each is just one big net. If you put your meter in ohms mode and measure across +5V and ground, you can expect it to read something in the few tens of ohms. If there was truly...

No, these shouldn't be tested with the flyback lead disconnected, and doing so would be incredibly dangerous.

Not normal for it to whine like that, certainly not enough to be audible over the fan. Could be the core in the flyback is ringing because the glue around it is cracked.

If you're interested in playing with electronics you may want to look at a used analog o-scope; for the same $60-70 you can find a 20/50MHz Tektronix scope for instance (occasionally 100MHz) with more channels and far greater usability.

You should expect to see something, but when probing the legs of the crystal itself, the load presented by the oscilloscope probe *may* cause it to stop oscillating or at least attenuate the signal. The fact that you get nothing on pin 5 of the 74S86 proves the oscillator circuit definitely...

Not too common for crystals to fail but given the condition your board is in, it wouldn't be all that surprising. Could also be a bad 74S86, but also check all the other components in the oscillator circuit around the crystal (R90, R91, Q10, Q11, etc). Somewhat sensitive circuit, if any of them...

Looking from the back of the machine with the rear bucket off, there's a green wire that goes from the CRT neck board, along the right side of the tube, and hooks onto a piece of metal braid running over the surface of the tube. Hook the clip of the discharge tool onto that braid or onto the...

I think Phipli is right in that a lot of the brittleness has to do with environmental conditions. My G3 desktop happened to be the most brittle Mac I've ever come across; between the latches that held the top case on, the flip-out foot, PCI slot baffle, drive carriers, all of it pretty much...

Wanted to answer these in case others land on this thread in future Google searches. The short answer: Replace the safety capacitors with parts of the same capacitance and safety class as originally installed. Or, longer: the safety capacitors, along with a choke, form the EMI filter at the AC...

You could do either. Removing the old and adding new would take longer but look cleaner. Adding just a little more to the old also adds the flux from the new solder to the joint (necessary to fix a cold joint). Applying liquid flux and then reflowing the joints with the soldering iron would have...

Glad to see it's working again but there's likely still a bad solder joint somewhere waiting to rear its head again. That or something wasn't connected properly the first time you were testing it. Would be a good idea to go through and add some new solder to all the joints on parts that are...

Start with the basics that have been mentioned in almost every thread concerning these machines. After reflowing/adding fresh solder to the joints on all connectors and heavy components, check the voltages at the external floppy connector. Check that the fuse isn't blown. X2/Y2 class RIFA caps...

Agreed and my apologies. Maybe instead of "not very much can go wrong" I should say: if something does go wrong, most of the time there will be a visual indicator (except, like you said, if a component gets fried due to hot air misuse). And so if a practice machine (like the LC II discussed...

Also, a couple notes with regards to tools, since there's a lot of conflicting information floating around online: contrary to what some guides imply, the latest and greatest soldering and test equipment are not a requirement for working on these 30+ year old machines. If you're happy with your...

As far as the capacitor replacement goes, there's not very much that can go wrong. If the board looks nice and clean visually, the capacitors are installed with correct polarity, the solder joints on the capacitors aren't cold (in other words, shiny, and with a smooth fillet between the leg of...

Salvageable for sure! Speaking from personal experience though: even if you have a fair bit of experience with SMD soldering, if you need a practice Mac I'd look for an LC-series machine instead, just because they have less "going on" on the motherboard -> less things to go wrong. That said, the...