Author Topic: Macintosh SE PSU IC identification  (Read 2074 times)

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Offline gkmaiaTopic starter

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Macintosh SE PSU IC identification
« on: November 30, 2020, 05:37:12 am »
That is probably for someone that is familiar with these old macs as there are no PSU schematics for the SE.

I got an IC that is faulty. I know that because I have two of these PSUs and by swapping the IC it works.
Could it be a high voltage optocoupler or a 177 opamp? Identification markings are 177  u8918. I could not find anything online so far... possibly remarked by manufacturer?

I wish I could tell more but that is all I know so probably someone that if familiar with this PSU and have had similar problem?! Maybe?
« Last Edit: November 30, 2020, 05:58:35 am by gkmaia »
 

Offline bob91343

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Re: Macintosh SE PSU IC identification
« Reply #1 on: November 30, 2020, 06:52:46 am »
8918 is the date code, 18th week of 1989, maybe May.

Since it's an 8 pin DIP I vote for an op amp or even a dual opamp.  Most optocouplers would have only 4 pins.
 

Online George Edmonds

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Re: Macintosh SE PSU IC identification
« Reply #2 on: November 30, 2020, 10:32:35 am »
Hi

Try the attached schematic
 

Offline Haenk

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Re: Macintosh SE PSU IC identification
« Reply #3 on: November 30, 2020, 11:02:31 am »
Can't make out any part numbers >300, so it's not the same schematics.

#deleted#
Looks like an Unitrode OEM part...
« Last Edit: November 30, 2020, 03:55:30 pm by Haenk »
 

Offline JKKDev

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Re: Macintosh SE PSU IC identification
« Reply #4 on: November 30, 2020, 11:45:02 am »
Wouldn't it be rather straight forward to test the working IC? Does it act as a diode on one side and a transistor on the other? If you drive the diode, does the transistor turn on? Then you have an opto.
 

Online George Edmonds

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Re: Macintosh SE PSU IC identification
« Reply #5 on: November 30, 2020, 01:34:43 pm »
The problem is that there is more than one variant of a Mac SE

George
 

Offline Haenk

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Re: Macintosh SE PSU IC identification
« Reply #6 on: November 30, 2020, 02:07:25 pm »
Wouldn't it be rather straight forward to test the working IC? Does it act as a diode on one side and a transistor on the other? If you drive the diode, does the transistor turn on? Then you have an opto.

a mil spec opto is unlikely IMHO
 

Offline CJay

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Re: Macintosh SE PSU IC identification
« Reply #7 on: November 30, 2020, 02:10:45 pm »
Given Unitrode tended to be *big* in SMPS controller ICs and that's from a PSU, I reckon there's a good chance it's something like one of the UC384x family, a wider pic of the rest of the unit and maybe the back of that board might be useful...
 
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Offline gkmaiaTopic starter

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Re: Macintosh SE PSU IC identification
« Reply #8 on: November 30, 2020, 06:57:53 pm »
Thanks! Ive tried a 8dip opto and no good. I will test the working one as an opto and let you know.
I am off on vacation and will send a photo when i am back. What i got so far are some plots of it. The ic in questio is within a sub board conected on test points p10,12,12,13.
« Last Edit: December 01, 2020, 04:48:02 am by gkmaia »
 

Offline gkmaiaTopic starter

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Re: Macintosh SE PSU IC identification
« Reply #9 on: November 30, 2020, 06:59:11 pm »
Is the image opening? I cant open it from my phone
 

Online fzabkar

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Re: Macintosh SE PSU IC identification
« Reply #10 on: November 30, 2020, 07:06:13 pm »
You have uploaded a zero byte file.
 

Offline james_s

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Re: Macintosh SE PSU IC identification
« Reply #11 on: November 30, 2020, 08:21:52 pm »
Draw up a schematic of the parts surrounding the IC and post that, it should provide some clues. I usually start by trying to identify the supply pins, ground is typically easy and Vcc is usually not too hard either. Then see if you can figure out what's an input and what's an output, there are a lot of parts that share common pinouts.
 


Offline gkmaiaTopic starter

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Re: Macintosh SE PSU IC identification
« Reply #13 on: December 01, 2020, 05:01:04 am »
The IC is on a sub board connected to the main board.

Not sure if it comes or goes to it but the +5v and the +12v (with signal for the CRT) goes through it.
 


Online fzabkar

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Re: Macintosh SE PSU IC identification
« Reply #15 on: December 01, 2020, 05:58:54 am »
There is an 8-pin uPC358C dual op-amp in that other circuit which is functioning as a voltage detector for the +5V and -12V rails. I suspect the "177" IC is also some kind of voltage or current sensing circuit.
 

Offline gkmaiaTopic starter

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Re: Macintosh SE PSU IC identification
« Reply #16 on: January 01, 2021, 06:17:21 am »
I am still stuck with this one.

I've tried a precision opamp op177 and no success. Also tried the conventional single and dual op amps no success...

Would the  IR2175 current sensing IC be an option?

I am gambling... I have absolutely no idea what this little daughter board does.

 

Offline CJay

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Re: Macintosh SE PSU IC identification
« Reply #17 on: January 01, 2021, 09:38:36 am »
Given Unitrode tended to be *big* in SMPS controller ICs and that's from a PSU, I reckon there's a good chance it's something like one of the UC384x family, a wider pic of the rest of the unit and maybe the back of that board might be useful...

 

Offline gkmaiaTopic starter

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Re: Macintosh SE PSU IC identification
« Reply #18 on: January 10, 2021, 08:38:12 pm »
Given Unitrode tended to be *big* in SMPS controller ICs and that's from a PSU, I reckon there's a good chance it's something like one of the UC384x family, a wider pic of the rest of the unit and maybe the back of that board might be useful...

Spot on!!! Thanks, the PSU works now!
 

Offline CJay

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Re: Macintosh SE PSU IC identification
« Reply #19 on: January 10, 2021, 10:11:03 pm »
Given Unitrode tended to be *big* in SMPS controller ICs and that's from a PSU, I reckon there's a good chance it's something like one of the UC384x family, a wider pic of the rest of the unit and maybe the back of that board might be useful...

Spot on!!! Thanks, the PSU works now!

SO, which chip was it? Only that might be useful for other people in future?
 

Offline vincomhk

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Re: Macintosh SE PSU IC identification
« Reply #20 on: May 25, 2024, 08:23:54 am »
I also have issue on the psu of Macintosh SE. Searched on web and found this post. Just to share the photo of that board with a relatively clear image of that IC for reference.
 


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