iicx power

[imactheknife]

I have a recapped iicx. The power button seems to work, as well as soft power. Only issue is if I turn on, then shut off the power button or keyboard doesn't turn it back on. It takes a few tries. Is this a PSU issue? my only working one at the moment. I don't have a pram battery in it at the moment either. Board was clean, no bad traces etc. Sound works, she boots fine when running. Thanks for any info.

 

[joshc]

Yes, weak trickle supply in the PSU is likely. They are known for it. A recap may help but I tend to say an ATX conversion of the PSU is better at this point. A PRAM battery is not needed for soft power to work correctly.

 

[imactheknife]

So when iicx is powered on, the power button doesnt shut off, i have to unplug it. Is this still psu? My iici acted this way but i cleaned all parts in soft power circuit and removed any ic chips to clean. She works fine now. Same psu i am using on iicx.

 

[joshc]

What happens when you choose shut down, does it think it has soft power and shut off or does it display the "It's now safe to switch off your Macintosh" dialog box?

 

[imactheknife]

When i hit shut down, it Shuts down completely.

 

[joshc]

So the power button works to switch it on, but not off? Or are you powering it on a different way? Sorry if you already explained that, just trying to make sure we're on the same page with what the actual behaviour is.

The IIcx has a somewhat odd startup circuit, similar to the Mac IIs and IIci, the schematics are here. I'd suggest poking around there to check for continuity if things don't seem right with soft power.

 

[cheesestraws]

https://www.downtowndougbrown.com/2015/03/explanation-of-the-macintosh-iiiix-power-onoff-circuit/ may be useful. This is where joshc's schematic comes from and explains it a bit.

The reason I think this is a good thing to look at for you is that there are two halves of the power circuit, and one deals with turning the power on and one deals with turning the power off. So, if you have trouble with only one of those, this is a decent place to start looking.

 

[imactheknife]

Ok, well i hope i didnt screw the thing. I tried to use my heat gun and remove the hc132 chips and f285 chips to clean underneath and check traces. I could not get those to come off. They had so much goop and corrosion maybe thats why? I used flux and solder wick to clean up legs and thought maybe that would be good for now. I thoroughly washed board, let dry and now just flashes light a couple of times when i hit power. No chime, no anything. I did find one bad trace and fixed it before i cleaned board. Did i bake those chips?? Normally my heat gun works fantastic.

 

[imactheknife]

ok, I was able to finally get this chips off (three in front of battery holder, and the row of three along the top. I cleaned all the goop, and checked traces. All seems good. Only issue, is it worth replacing those ic chips if still available? or just put old ones on and try it again?

 

[AwkwardPotato]

If you think there's a chance you might've baked the chips with the heat gun, I'd honestly just go for replacing them. Those parts are still available and cost pennies, would potentially save you the trouble of having to desolder the old ones yet again

 

[imactheknife]

Ok, thanks, appreciate the response
. Is that something mouser would offer? Will do some googling and see.

 

[AwkwardPotato]

Yep, both appear to be in stock at Mouser. They're pretty bog-standard parts.

 

[imactheknife]

well, I decided to out them back on. the soft power works. I Can turn on with keyboard or power button. It will also shut off. I am getting death chimes now lol..can't win with this one

 

[imactheknife]

Is these chips memory related? Like i said soft power works, power works, but death chimes. Wondering if it is ram issue?

 

[AwkwardPotato]

Yes, the 258s form the address mux for the RAM. If any of them fail it absolutely will cause death chimes.

 

[imactheknife]

Ok, thanks again. I can’t find any parts that match the f258ad. Do you have a possible link for those. Sorry to be a pain! My search isn’t bringing anything up. I have an account with mouser.

 

[AwkwardPotato]

Searning "74F258" brings up this item. Should've linked it in my last post, my apologies.

 

[imactheknife]

Searning "74F258" brings up this item. Should've linked it in my last post, my apologies.

Thanks! I ended up soldering old chips on, checking the legs for nice shiny clean connections and she is back up and running with power and soft power working. So, not needed now hopefully. Thank-you for the help!

 

[joshc]

Glad you got there in the end, those chips get badly affected by cap goo and as @cheesestraws pointed out, the power on and power off portions of soft power are separated so you can have one working and not the other, depending on what has gone wrong.

 

[imactheknife]

Well, back to turning on by itself lol. So maybe new parts are needed. The psu is working great, so i know that’s fine