Macintosh SE and PRAM

[XboXC]

Hi. A few months ago I repaired Mac Classic. Today I have a SE model. Now I have a problem with PRAM.

I installed a new Lithium battery, but mac still can't save parameters to PRAM (eg. speed of mouse). Where is PRAM chip? Or what's going wrong?

 

[XboXC]

OK. I found it. The PRAM is in RTC chip on board. But I can't find those chip 8833MPG, apple part 343-0042-B.

 

[unity]

You will probably need another chip from another board. Did you check to make sure the battery is installed correctly and has voltage? I assume you did, but need to ask.

 

[XboXC]

The battery is new. I replaced it few weeks ago (and it has a 3.54V now). My problem is in my country. I living in poland and here is very hard to find any part of apple. Of course I can buy other Mac SE but this is not what im find.

 

[unity]

After replacing the battery, did you try a PRAM reset then setting things again? Command(the Apple key)+Option(the Alt key)+P+R

 

[XboXC]

Yes but nothing happen. Today i found a broken pin on rtc chip. So propably this is my problem. I can replace this chip but i can't find any information or pages of this RTC chip. Maybe i can buy broken board from other mac but all boards on ebay is working and its very much $ for me. If someone has old broken board please contact.

 

[unity]

I have a ton of extra SE boards. But shipping would be a bit prohibitive. If you can post some pics of the exact chip you need, I can probably hot air remove a couple and ship them in an envelope. That would be much less expensive.

 

[XboXC]

If you have that chip is very helpful for me. So this chip is markered on board as "RTC" and it's a model 8833MPG and apple part 343-0042-B (maybe you have a another version, but it's nevermind).

 

[Elfen]

"RTC" means Real Time Clock. Maybe another RTC Chip can be used in its place?

You checked the traces leading to the chip and made sure they are OK?

 

[unity]

If that is what you need, I am sure I can pull some for you. I do agree that I think thats the clock chip, not sure how it can influence PRAM but it might. If the clock is not working, maybe PRAM fails? I will let you know this weekend. In the mean time, I would reflow any suspect solder points and verify cap installation.

 

[XboXC]

The PRAM is in RTC chip. I have a Apple Guide Family and i know - the PRAM is there. I resolder all caps on board and replace it. The chip is phisicaly broken (one pin is break off).

 

[Elfen]

You can try to Frankenstein the chip by cutting part of the plastic around the pin to expose more metal, and then solder a wire from the metal to the board and see if that works. You just need to cut out a tiny amount of plastic.

 

[Paralel]

I agree with Elfen. If you want a perfect fix, replace the chip, but you should easily be able to repair a busted leg on the RTC chip.

 

[XboXC]

No no. This leg is broken in chip. Is no cut, but is ripped from chip.

 

[trag]

Some useless info I wish to preserve since I went to the trouble of hunting it down. The emblem on the RTC is for IMP, International Microelectronic Products, Inc.. they were founded in Silicon Valley in 1981 and seem to have existed until about 1989. No datasheets or books appear available electronically, after a cursory search. I also didn't figure who, if anyone immediately succeeded to their IP. Dialog Semi says they grew out of IMP but it doesn't seem like a product successor, more like where some employees went or something.

The relevance here is that in the 80s there may have been a data book with an IMP8833 or similar described in its pages.

 

[Paralel]

A totally missing leg? That's a different story, you'll def. have to replace it with a donor part.

(I wonder how a leg was completely ripped out...)

 

[XboXC]

This text is copied from "Apple Guide Family":

The Macintosh real-time clock (RTC) is a custom IC that is interfaced to the main logic
board by a VIA. The real-time clock used in the Macintosh SE, Macintosh SE/30, and
Macintosh II-family computers is an upgraded version of the custom IC used in the
Macintosh Plus and earlier Macintosh computers.  (...)

The RTC also contains 256 bytes of RAM (20 bytes in the Macintosh 512K and Macintosh 128K, 128 bytes in the
Macintosh Portable), called parameter RAM, that is powered by a battery when the
Macintosh is turned off (...)

So, the RTC is a custom chip and propably it can't buy as part, but only with all SE board. And I don't think there is another chip that can replace a original chip and working fine.

 

[Paralel]

I would say you are likely correct. Sounds like it was a custom Apple part. I hate those damn things.

 

[Elfen]

No no. This leg is broken in chip. Is no cut, but is ripped from chip.

This is impossible without catastrophic failure of the chip itself (a damaged casing with a huge chunk of it missing - see diagram) as the pin is anchored inside the chip itself.

I believe that the pin broke flush to the side of the chip. And as I described before, it's an easy fix. You need to trim a tiny bit of the epoxy/plastic casing above the pin to expose some of the metal anchor. This is where you can solder a wire to the exposed metal and then to the logic board. It will not be a pretty repair but it will be a repair that will work.