Macintosh IIci — #26

Post #26 by z80.eu

Source Forum	Macintosh IIci — #26
Category	Hardware
Post Date	Mon, 9 Nov 2015 - 07:44
Original URL	https://68kmla.org/bb/threads/macintosh-iici.2663/

Post

Schmoburger said:
Before I go any further, I must call a point of order...I cannot help but to detect a hint of passive-aggressive, sarcastic scoffing in the tone of the above post. I am unsure as to whether you meant it to be condescending in nature or not, but it certainly does have a rather derisory air which really is unneccessary and quite unwelcome.

[...] deleted a lot of more criticism

The battery should not make a huge deal of difference to the power-on sequence of a IIci, but if you feel that it could be the grail you seek in the quest for IIci goodness, by all means it will do no harm to replace it, as brand new units are cheaply and readily available on fleabay for very little money... My adivce would be to go with the Saft or Varta brand as a known reasonable brand. There are other far cheaper brands from Asian distributors and manufacturers that might seem tempting due to their miniscule pricetags, but personally, I wouldnt be one to trust them.
From what you are describing, it almost sounds as though the power supply has failed... I have had a number of different Mac's behave similarly shortly before failing to power on at all or having the PSU go bang. What portion of the unit has failed if this is the cause is entirely anybodies guess... the obvious course of action before anything, if you are 150% confident that all components on your logic board are servicable and that your solder work is sound, would be to open the PSU and see what you can see... if there are any obviously burned or blown out components, this is likely where your problems lie. Even if not, PSU caps fail just like any other electrolytic caps, so it would not hurt to replace them all as well, because like the ones you just replaced on the logic board, they are quite likely already failing and falling out of spec even if they don't yet appear physically damaged.

Ideally, to identify definitively whether you are dealing with further logic board problems or a power issue , you would be best served to get hold of a known working power supply and see if the machine functions differently... If not, you could be looking at electrolyte contamination, electrolytic rot of chips, or any other number of component failures on the logic board, or even the possibility of a bad joint on your new soldered components or even stray slag causing a short... Now I know one might be tempted to take offence to the mere suggestion that one's solder work is anything but exemplarary, but the reality of the situation is, solder is difficult to negotiate sometimes, and we are all human. None of us are perfect, and I have even seen highly skilled technicians pull their hair out for hours over faults that turned out to be a simple case of stray solder causing a short in a place that wasnt at first obvious. It could even be a broken or corroded circuit trace... just one is all it takes, and it's not hard to sever once with an accidental slip of a screwdriver.

Excuse me for being sarcastic, but very often almost all problems which can occur are reduced to "capacitor" problems only.

Many (almost all?) forgot, that there are also semiconductor stuff in it, and that thermal load will shorten lifetime of these components, too.

Also, I suspected also the dead battery, because someone here already asked what dependancy are related to the batterty / what function is covered by the battery also.

And finally, it is not necessary to be the upholder of moral standards, I agree that this board should be used for exchanging information and (sometimes) fun only, yes.

I wrote already that I replaced for test purposes the power supply and the bad "start" behaviour did not changed, so I can exclude the power supply itself as a reason.

Last but not least for further examination, I need a schematic diagram, or even better, test points with voltage values or oscilloscope screen images (can be often found for monitors also).

I fear test points with voltage values and/or oscilloscope screen images (for comparison purposes) will not exist, and I'm unsure if I am able to use a schematic diagram for diagnostic purposes (I studied computer science, not electrical engineering). Finding a contamination with weak acids from a bad capacitor should be easy if the circuit traces are (visually) affected, but I am not an expert in circuit traces.

May be the hint about the diodes (the ones in row) is important too, will look for these also.