UPDATE: The PowerBook arrived on Thursday and it is in really good condition except that it does have the hinge signs that za9ra22 mentioned. It still holds nicely and isn't all that bad (I'll post pictures later).
Upon initial receipt it didn't power on at all. I measured the power supply with a meter and didn't get anything. So I figured I'd have to deal with that. Took it to the basement workbench, plugged it in and lo and behold it was now working. So I eagerly went back upstairs to plug it into the PowerBook. Success! The system powered on and I was pleased. Very nice system and it reminded me of how good MacOS really was (from a useability perspective). I much prefer its interface to OS X / macOS.
Unfortunately when I went to power it on over the weekend...nothing. I know the power adapter is working as the power indicator light in the upper right of the screen is illuminated. I decided to pull the battery to see if a dead battery might be drawing too much power and affecting the system. Nope, even with the battery removed it refused to power on.
I disconnected the power adapter and let it sit. Plugging it back in and it powered right up (interestingly it powers on when I plug in the power adapter, I don't need to use the power button). In previous testing I noticed the brightness and contrast buttons didn't seem to work. Thinking these might be controlled via software I went to the Control Panel to see if there was a way to adjust them through there (the screen is bright and easy to read as it is but I should be able to change these in some way). Unfortunately while doing this the system just powered off and refused to power back on with the power button (the power button does power the system on if I power the system off but it hasn't ever powered it on unless I have done that).
Plugging and unplugging the power supply doesn't power on the system. It appears I have to unplug it, wait a short period of time, and then plug it back in. Unfortunately it continues to power itself off shortly thereafter. Unless someone has any ideas it appears there's something wrong with it.
I've reached out to the seller and they claimed it did work when they last used it but it had been a while. I'm a little bummed as this is a really nice system (came with an Apple case and original manuals) save for the 5300 curse.
I did note from za9ra22 post that there was an issue with the power connector and that the cabled might need to be positioned a particular way. Moving the connector while plugged in doesn't appear to change anything. How easy is this system to disassemble? I'd be willing to keep it if I can service it myself but if it's going to be an issue then I'll probably end up returning it (something I'd rather not do).
The 5300 will power on directly from plugging it in if the PRAM battery is dead - it doesn't mean there's a problem with the power button, which will work perfectly normally as long as the computer remains powered. Quite a few of the PowerBooks around this time behave the same, so it's normal.
The original power supplies can be rather fickle - I have two of them and they usually work, but one or other sometimes doesn't seem to. I have a modern replacement which is consistent.
If the power light on the screen comes on when you connect up the adapter, that is the so-called 'green light of death (GLOD) and it means the system has failed and can't start. It sounds fatal, but usually isn't, and usually clears with a reset (little rectangular button on the back on the 5300). The power light on the top-right of the screen should only light when the system is sleeping, and it will then flash every second.
The problem with the 5300 and uncommanded powering down is likely to be a loose power connector - as described previously - where it typically needs re-soldering on the logic board. This can also cause issues getting the system powered up, because when plugging the adapter into the back, the connector itself on the board isn't making proper and complete contact. Sometimes very gently wiggling the power connector helps - but likewise, with a loose connector not firmly attached to the board, it sometimes also makes it even more loose.
To make matters worse, if the screen is showing signs of hinge problems, it means they are very likely to fail, and the screen will not rotate smoothly - instead it will appear to pull forwards on one side or the other, so it no longer fits flush into the lower case. It will likely also feel very stiff when opening or closing.
They can be helped by opening/closing them with pressure on the hinge area at the bottom of the screen, rather than leverage on the top edge of the display, but hinges are very weak on this design, and most 190/5300s show signs of this problem. I have a 190 which works well, but the left-hand hinge is almost totally broken, so I no longer use it.
Disassembly isn't a big problem, so resoldering the power connector on the logic board is pretty easy, if a little fiddly and time consuming, but I don't know of any way to repair the hinges, other than with replacement parts as and when they might be available of eBay, or perhaps from a parts machine.
A useful source for repairing/troubleshooting these systems is the PowerBook 190/5300 Service Source from Apple. (PDF attached)
The 5300 is a great PowerBook if you get a good one, or have the parts to repair one and make it good, but it was a fatally flawed design in terms of hinges and power connector. I have 2 190s, both with hinges failed, and 3 5300s, one has a broken power connector, one an intermittent power connector and creaky hinges, and the last one was a new old stock unit which was from the repair program and never put into circulation, so is perfect.... so far.
For reliability and better robustness, a 3400 would be more recommendable, though rather bigger and heavier. The advantage of the 190/5300 is that it is very compact since it wasn't designed to accommodate a CD drive.
