Macintosh SE PSU IC identification

[gkmaia]

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?

[bob91343]

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.

[George Edmonds]

Hi

Try the attached schematic

[Haenk]

Can't make out any part numbers >300, so it's not the same schematics.

#deleted#
Looks like an Unitrode OEM part...

[JKKDev]

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.

[George Edmonds]

The problem is that there is more than one variant of a Mac SE

George

[Haenk]

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

[CJay]

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...

[gkmaia]

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.

[gkmaia]

Is the image opening? I cant open it from my phone

[fzabkar]

You have uploaded a zero byte file.

[james_s]

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.

[Haenk]

I have found a a link to 1987 / 1992 parts, not a lot of DIP-8 in there:

http://bitsavers.informatik.uni-stuttgart.de/components/unitrode/_dataBooks/1987_Unitrode_Linear_Integrated_Circuits_Databook.pdf

http://bitsavers.trailing-edge.com/components/unitrode/_dataBooks/1992_Unitrode_Product_and_Application_Handbook.pdf

[gkmaia]

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.

[gkmaia]

I have found a a link to 1987 / 1992 parts, not a lot of DIP-8 in there:

http://bitsavers.informatik.uni-stuttgart.de/components/unitrode/_dataBooks/1987_Unitrode_Linear_Integrated_Circuits_Databook.pdf

http://bitsavers.trailing-edge.com/components/unitrode/_dataBooks/1992_Unitrode_Product_and_Application_Handbook.pdf

Awesome will dig those!!!

[fzabkar]

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.

[gkmaia]

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.

[CJay]

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...

[gkmaia]

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!

[CJay]

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?

[vincomhk]

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.