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IIsi repair after extensive battery corrosion

belzrebuth

Well-known member
I was a given a IIsi in a pretty bad state, the battery has leaked damaging the CPU IC (corroded leads which instanly broke upon touch) and several corroded traces throughout the board.
I've cleaned the board the best I could and repaired a couple of traces they were apparently damaged.
I also replaced the CPU with one I found on eBay https://www.ebay.com/itm/392523139565.
The power supply has also been recapped and capacitor leakage cleaned but I couldn't get it to power up so I wired an ATX power supply to check if the mainboard actually works, and it doesn't! I get no bong chine upon power up.

I don't know if the CPU replacement is actually real/working or if there are still any damaged traces on the board but I thought I could ask a few questions first.

So my questions are:

1) Do I have to have a battery connected to get video out?
I guess the absence of a bong sound at power up indicates there's a problem elsewhere but I thought I'd ask anyway.

2)Some capacitors are still missing, could this be causing a no-bong/no-video situation?
Do all capacitors need to be installed in order for the machine to boot?

3) Has anyone replaced the CPU on a IIsi or another machine with a questionable replacement?
If so, did it work?
 

joshc

Well-known member
1) Do I have to have a battery connected to get video out?
Nope, IIsis work fine without a battery installed.

2)Some capacitors are still missing, could this be causing a no-bong/no-video situation?
Capacitors are part of the audio circuitry so i'm not surprised there's no chime with capacitors missing.

3) Has anyone replaced the CPU on a IIsi or another machine with a questionable replacement?
I'm less certain on this one, but a lot of processors on eBay are not what they say they are. But if you have a scope, you'd be able to check for the clock signal on the processor.

so I wired an ATX power supply
How are you trying to switch the Mac on? Via the switch on the board, or via an ADB keyboard? These Macs have soft power and won't just turn on with an ATX PSU (depending on how you'v wired it up).
 

belzrebuth

Well-known member
Thanks for the quick reply!
I installed the rest of the capacitors but still no chime.
I've wired the power supply as follows (looking at the connector as if the mainboard is directly in front)

GND + || + +5V standby from ATX (purple)
+5V + || + NC
+5V + || + -12v
+5V + || + GND
+12V + || + GND

I found this exact pinout a couple of times (different images) so it should be correct.
I also shorted the ATX green wire to GND and I power the IIsi by switching on the power supply via its switch.
I can hear a slight pop on the speaker and the green LED switches on.
Also the CPU is getting warm (not hot)
Should I plug an ADB keyboard to it? Does it need to power on differently (e.g shorting the ATX main switch and leaving the green wire floating)?!
I believe I've seen a YouTube video where a IIsi turns on from an ATX supply without any keyboard attached and it seems that mine does power on as well.
I also get +12V on the fan contact ( I don't have mine plugged in at the moment).
I don't have anything else attached to the logic board (HDD, floppy or any additional RAM).
 

belzrebuth

Well-known member
Forgot to mention that the 50.something XTAL is missing from the board.
I believe that could be important in a video mode that requires it, don't know if its absence can prevent the machine from booting up.
 

belzrebuth

Well-known member
Unfortunately not. I waited more than a minute but no boot.
My guess is that there's maybe a trace or a via not making contact. The battery leak was pretty heavy on the board and I only found 2 traces not making contact.
It makes sense to have missed something so I should recheck everything more closely I guess.
And I should also probe around for vital signs like CPU clock, address bits etc.
I haven't measured anything yet aside from the PSU voltages.
 

robin-fo

Member
Did you also try to power up the PSU (by connecting PS_ON to GND) immediately after pressing the IIsi's power button?
 

belzrebuth

Well-known member
The IIsi power button is not pressed...I just leave it in the default position all this time since I think I'm force feeding the ATX voltages anyway.
Does it need to be pressed?
 

robin-fo

Member
Apparently the ADB controller expects the PSU to power up while the power failure warning signal (generated by the ADB controller using the +5V standby voltage) is high. If you press one of the power buttons, this signal gets pulled high for 1-2 seconds. Otherwise, if you immediately apply 5V to the board, the reset signal is pulled low for some time thus preventing the system from booting.

At least this is what I measured and observed on my own IIsi...

Btw the cpu on mine gets hot (maybe 50°C) as well.
 

belzrebuth

Well-known member
Okay thanks for clarifying,I left the power button screwed at the "on" position and wired a switch between the PWR_ON (green wire) and GND of the ATX supply.
Powering it on this way returns the same exact result.
So I was powering it up the wrong way but there must something else preventing it to boot anyways.
 

belzrebuth

Well-known member
Yes..I would expect this board needs a bit more work in order to boot again.
It was looking like it was found in the sea when I first got it.
Now while it looks better I'm not so sure I've checked *everything*.
I will post back when I have updates!
Thanks for the help:)
 

joshc

Well-known member
@belzrebuth When I recapped my IIsi, I had to remove a lot of chips around the capacitors in the sound circuitry as everything was caked in cap goo. Are you sure the sound chips etc are clean?

Can you post some hi-res photos of your board, maybe one of us can spot something that doesn't look right?
 
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