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UBHappy
March 10th, 2011, 12:13 PM
I have an original Mac IIx (no upgrades or modifications, one video card, no other cards in the card slots) connected to a Hi-Res RGB monitor that is having start-up problems. This computer is usually stored in a bedroom closet and is used only rarely. The last time that I successfully used this computer was in February, 2008.

Specifically, my Mac IIx will not start-up from the Power Key on the Apple Desktop Bus (ADB) keyboard. After numerous failed start-up attempts via the Power Key, I searched through several forums and found this universal advice about Mac IIx start-up problems:

1) Check/ change out the two batteries (Varta Lithium 3.6V and 3.0V) on the motherboard. I understand that one battery (3.6V) is used to start the power supply unit (PSU) by sending a momentary +3.6V pulse to pin 15 of the PSU through the Power Key on the ADB keyboard and the second battery (3V) is used to maintain the PRAM (parameter random access memory) chip that stores computer startup information. I understand that a low PRAM battery can also cause start-up problems with the Power Key and can cause No Video problems with the monitor.

2) One or more capacitors on the motherboard may be defective (leaking) and need to be replaced.

3) The PSU may be defective and needs to be replaced.

I opened up my Mac and found no visual problems with any of the capacitors (no leaks, no corrosion), so I assumed that these were not the issue.

I then checked the two Varta batteries (both 20+ years old) and found both to be slightly below spec (2.8V for the 3V battery and 3.3V for the 3.6V battery). To temporarily correct for these weak batteries I constructed two 3.6V “battery booster” power packs by connecting three fully charged NiMH AA batteries in series. I then connected one 3.6V power pack in parallel with each Varta battery on the motherboard using insulated alligator clips. The voltage across each Varta battery was now 3.6V which should have been adequate for Power Key startup.

After putting the battery boosters in place I was still not able to startup from the Power Key. I was able to startup the PSU by sending a +3.6V pulse directly from the start-up battery to pin 15 of the PSU using a jumper wire. The PSU seems to power up normally and I hear the initial startup beep followed by some spinning sound from the hard drive. Unfortunately there is no video display on the RGB monitor throughout the startup so I really do not know the status of the startup process. The ADB keyboard remains non-responsive (no indicator lights, no response to any keys) throughout the start-up process.

I am at a loss in terms of what else to check. I would welcome any suggestions to help me troubleshoot this startup problem. Thanks.

Unknown_K
March 10th, 2011, 01:28 PM
Both batteries should be the same voltage (3.6V new), why do you have a 3.0V one? I would replace both batteries before I did anything else (make sure the +/- is orineted correctly). There is more to a battery then voltage, you have current issues (especially if one of the batteries is used to kick start a power supply) so even if the 3.6V pulse started something it might not have been long enough to get the machine going correctly.

UBHappy
March 10th, 2011, 03:55 PM
Both batteries should be the same voltage (3.6V new), why do you have a 3.0V one? I would replace both batteries before I did anything else (make sure the +/- is orineted correctly). There is more to a battery then voltage, you have current issues (especially if one of the batteries is used to kick start a power supply) so even if the 3.6V pulse started something it might not have been long enough to get the machine going correctly.

Thanks for your response. I am not sure why I have two different batteries but I attached a picture that shows B2 as a Varta 3V Lithium (I measured 2.8V across this battery) and B1 as a Varta Lithium that I assume is 3.6V (I measured 3.3V across this battery). Both of these batteries are original.

I was planning to replace both batteries with two Saft LS14250C Lithium 1/2 AA 3.6 V batteries with solder tabs, but I first wanted to confirm that the original Varta batteries were the actual cause of the startup problem. I thought that connecting a 3.6V “booster battery” power pack in parallel with each Varta battery on the motherboard would compensate for the weakened Varta batteries and would allow the Mac IIx to startup through the Power Key. Unfortunately this did not work and I am now concerned that there may be other troubleshooting issues. Is there any reason that the “booster battery” power packs would not compensate for the weakened Varta batteries?

I appreciate your insight.

Tom

Unknown_K
March 10th, 2011, 07:40 PM
Could be you have bad capacitors on the motherboard. I have a spare IIx motherboard (own 2 perfectly working units) that needed recapped but works fine now (also had the original batteries removed and replaced with removable battery carrier). Recapping a IIx is pretty easy.