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How to turn on a IIci PSU outside the computer?

superjer2000

Well-known member
@olePigeon Check it connected to the motherboard. You should be able to find a way to jumper those pins and then attach the PSU. Just make sure it’s the right pins.
 

olePigeon

Well-known member
@superjer2000 Well, I was poking around with my multimeter following the soft power circuit diagram. Resistor C26 which is supposed to be 4.7k is open. So I think I've already found at least one bad resistor. Hopefully it's just the one.
 

olePigeon

Well-known member
I found the short. The 8-pin chip thingy at L1. FIL-MAG 94Z46011 155-0007-F. I have no idea what this thing is, and Google is short on answers other than it's an obsolete part.
 

olePigeon

Well-known member
D10 diode doesn't diodify when the chip is installed, so the short is somewhere else. It's allowing about 50% power both directions. C26 shorted, of course.
 

re4mat

Well-known member
Yeah, you have to give it a load, otherwise it will trip the OVP and shut down pretty immediately. You don't have to use high power resistors, but here's an example of some hooked up to a Macintosh II PSU to give it a load. This PSU was successfully bench tested like this without connecting it to the logic board:

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olePigeon

Well-known member
So I took C26 out again. It's not shorted, but it's a 474 capacitor. It only reads 10nf on my tester.
 

olePigeon

Well-known member
Nevermind, the silk screening was coming off. It'a IA4, not 474. It's a 10nf cap. Working as intended.
 

olePigeon

Well-known member
I know stuff is shorted. But, the second UE13 is fine. +5v goes to +5v, ground goes to ground, everything is isolated. But the first UE13 and the HC74A (UB13) appear to be shorted. I'm using the circuit diagram from another thread, attached below. The red circles show all those pins tied to ground, but they shouldn't be, should they? UB13 pins 10 and 13 should be +5v, with 11 & 12 on ground. But all of them are connected. The first UE13 (just above UB13), pins 1 & 14 are tied to ground. They should be +5v.

How likely that it might be one of these chips? I don't have a heat gun or chip quick, this is going to be tough to remove if I have to go that route.

Anyone have any ideas?
 

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superjer2000

Well-known member
I know stuff is shorted. But, the second UE13 is fine. +5v goes to +5v, ground goes to ground, everything is isolated. But the first UE13 and the HC74A (UB13) appear to be shorted. I'm using the circuit diagram from another thread, attached below. The red circles show all those pins tied to ground, but they shouldn't be, should they? UB13 pins 10 and 13 should be +5v, with 11 & 12 on ground. But all of them are connected. The first UE13 (just above UB13), pins 1 & 14 are tied to ground. They should be +5v.

How likely that it might be one of these chips? I don't have a heat gun or chip quick, this is going to be tough to remove if I have to go that route.

Anyone have any ideas?
You’ve got a ton of corrosion on UD13. I am betting there is a lot of cap too under there too. You’ll need to check continuity to all of the points suggested by the soft power schematic. Those chips are all still available and I would replace them but ultimately they may need to be cleaned underneath.
Order some chipquik and come back to it would be my recommendation.
 

olePigeon

Well-known member
OK, ordered a new set of Red Caps, 2x MM74HC132M‎, 1x MC74HC74ADG‎, and 1 pack of Chip Quick SMD removal. Hope to get it by the end of the week.
 

olePigeon

Well-known member
Sigh. While there was a ton of crap under those ICs, after removing them, the short is still there.

I've about exhausted my ability to diagnose this board. Unless someone else has any ideas. I need to source another IIci board.
 

superjer2000

Well-known member
Sigh. While there was a ton of crap under those ICs, after removing them, the short is still there.

I've about exhausted my ability to diagnose this board. Unless someone else has any ideas. I need to source another IIci board.
I found the power circuit schematic you referenced to be fully accurate when I fixed my IIci. There were about three jumper wires I had to add. Note that pin 1 might between the chip and Apples markings on the logic board (I think and I can’t recall which defence is used by the schematic)

For the short can you confirm specifically which pins and contacts you are seeing as shorted but you believe shouldn’t be. A picture with arrows on would be helpful to make sure there isn’t any confusion on pin #s. I can check my IIci with a working circuit and let you know if I see shorts in the same places or not.
 

olePigeon

Well-known member
@superjer2000 Sure, I can do that when I get home. Perhaps it's supposed to be shorted? But, it seems odd.

Edit: I can tell you it's the pins on the ICs pictured above, but also the capacitor at C26 (pads shorted, cap reads fine at 10nf out of circuit), the diode at D10 (reads about .25 volts both directions when in-circuit, works fine out of circuit single-direction .56v or something), and another diode I tested (forgot which) up near the ADB filter. Again, signals both direction when in-circuit, but works fine out of circuit.

Seems to me those diodes shouldn't be letting power both ways. And it seems like 5v shouldn't be shorted to ground?
 
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olePigeon

Well-known member
@superjer2000 OK, some interesting developments. I replaced all three 3 ICs and ran a bodge wire from a missing pad (it had completely corroded away.)

Great news is that the computer now turns on. Yay! Bad news is that it always turns on no matter what. It's like I have the power switch on the rear pressed in. However, after it boots, neither of the ADB ports work. Some Lycosing indicates that non-working ADB ports is a bad ADB filter.

So back when I thought the filter could be bad, all the shorts disappeared when I removed it. So now I'm leaning back towards a bad ADB filter. It didn't occur to me that the filter is bunch of capacitors, and mine is completely shorted open. Fortunately my IIci has both DIP holes and IC pads for a filter. So I think I can steal a filter from another computer with ADB ports, it doesn't have to be the DIP version. I'll try swapping out the filter tomorrow and see how it goes.

I'm hoping I can just buy a generic filter, but I don't know what part to look for. I couldn't "find an alternative" on Digikey or Mouser.

In the meantime, I'm pretty happy with my rework. Especially my bodge wire. I got a nifty metallic blue teflon wire from the recycler. My handy work is all hidden under the power supply, though.

iicib1.jpg
 
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