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Thread: IIx Soft Start Not Working


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Permlink Replies: 4 - Pages: 1 - Last Post: Feb 24, 2015 2:18 AM Last Post By: tt
tt


Posts: 144
Registered: 8/25/12
IIx Soft Start Not Working
Posted: Feb 23, 2015 1:46 AM
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Attachment DSC01048.jpg (751.0 K)
Attachment DSC01044.jpg (795.5 K)
To continue from dougg3's thread here: https://mac68k.info/forums/thread.jspa?threadID=338&tstart=0

tt wrote:
On my IIx board I replaced UB1 and UB2 and it still does not soft start. I probably should have left them on... I noticed that half the circuit seems to be devoted to soft - starting through the rear switch and half through the ADB keyboard power-on button. So I attached a keyboard and confirmed the keyboard portion is working properly. Did you try turning on through the keyboard?

dougg3's response:

dougg3 wrote:
Hehe, well glad to see you're still around! I tried both the keyboard and the rear switch, and both methods didn't work. Now that I've traced out the whole startup circuit, I'm pretty confident mine will work after I use known-good new batteries though. There were definitely broken traces though, so I still needed to repair it even if my batteries were half of the problem.

I originally thought the top half of Gamba's startup circuit was for the ADB power button and the bottom half was for the rear power button, but I was wrong. Actually, most of the startup portion of the circuit is shared by both the keyboard and the rear power button. The top part of the circuit is for power on, and the bottom part of the circuit is for power off. UB11 (VIA2) pin 13 is the /POWEROFF signal that tells the power supply to shut off. The power off circuit is also hooked up to the second pole of the power button in order to enable pushing the power button to shut off the system.

If your rear power button doesn't work but your keyboard power button does, there are only a few connections that could be causing that problem. I would verify the connections on R9 and C3 (and their connection to the power button). It could also be the connection from R3 to the power button. Everything past R3 is shared by both the keyboard and the rear button.

I didn't notice a typo on Gamba's schematic, but he did note that the components are for the II -- the IIx may be different. My IIx seems to have different component numbering from most, so mine actually matched Gamba's diagram.

Thanks again for this info. I have attached a couple pics here of my board. The resistors are on the back side and it looks pretty much pristine on the back. I am thinking it is either C5 or C6 that has the issue here. I'll probably take off these capacitors and check underneath them. Does C5 on my board map to C3 in gamba's schematic?
max1zzz

Posts: 4
Registered: 1/18/15
Re: IIx Soft Start Not Working
Posted: Feb 23, 2015 10:08 AM   in response to: tt in response to: tt
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Have you checked the connection from the power switch to L4? On both the IIx's i have had that trace has been bad, and yours is a little corroded looking
dougg3

Posts: 190
Registered: 8/13/12
Re: IIx Soft Start Not Working
Posted: Feb 23, 2015 10:36 AM   in response to: tt in response to: tt
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No problem! For sure the damage is on the top -- it may be a trace somewhere on the top that goes to a via that goes down there. Your C5 and C6 map to my C3 and C4, respectively. I would verify continuity between all components on that section of the schematic (C3, R9, power switch, R3).

It appears to me that a broken trace from L4 (L2 on mine) to the power switch is definitely a good idea to check too as max1zzz said. Now that I look closer at the schematic, it all depends on where R3 makes its connection to that circuit. If R3 is connected closer to L4 than the rear power button (and it sounds like it is, according to prior notes), that could definitely make only the keyboard power button work. Good point max1zzz! So add L4 (L2 on Gamba's schematic) to the list of components to verify the continuity between.
tt


Posts: 144
Registered: 8/25/12
Re: IIx Soft Start Not Working
Posted: Feb 23, 2015 1:21 PM   in response to: dougg3 in response to: dougg3
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Thanks guys. I'll check the line going to L4 (pin 4 according to the link dougg3 provided) from the switch. The trace that goes between C5 and C6 that has some corrosion looks like it is the connection that goes way over to UB1-1. I'll check that connection also.
tt


Posts: 144
Registered: 8/25/12
Re: IIx Soft Start Not Working
Posted: Feb 24, 2015 2:18 AM   in response to: tt in response to: tt
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I checked the connection between the switch and L4 and it was open. So I patched it on the underside of the board and it seems to be working as it should. I need to install my battery board to be completely sure since I had some batteries with lead wires loosely inserted into the open through holes. Thanks guys for pointing me in the right direction. I should have posted sooner. :)

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