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First Macintosh Classic II trying to fix


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Hi guys, last days i got for free a Macintosh Classic II that need restoration and fixing. I uploaded some pictures on imgur and as you can see the issue is the classic vertical bars. I read online that for similar issue need recapping. I cleaned the board with distilled water and some soap and let it dry, then i cleaned again with lot of IPA 99% and I recapped with THT capacitors (I didn't have the smd ones cap at time). Some pads lifted off because i didn't use immediately the hot air station, but I recovered as you can see in pictures. After many cleaning and many tests the issue remains. I checked the MC68030 clock with multimeter (i don't have an oscilloscope) and i got 2.42v and I suppose could be ok by the assumption of 5v / 2. The reset pin on cpu is ok too it change state from LO to HI at power on and when i press the reset button. The board is version 820-0401-B. I didn't recapped the analog board because i verified the voltages on the connector that goes on logic board and i have +12v, -12v, +5v and +5v. Now I'm a bit stuck and I'm out of ideas as this is the first time I try to fix this kind of computer. I really need your help and any suggestion is appreciated. Thank you so much in advance!

 

https://imgur.com/a/yJtGftx

 

Edited by hyuma
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  • hyuma changed the title to First Macintosh Classic II trying to fix
1 hour ago, erichelgeson said:

Have you taken out the ROM chips, cleaned and re-seated? That is a common step I've had to do once or twice to get past. Just make sure you check/remember the orientation and the offset.

Yes I tried that!

 

19 minutes ago, 360alaska said:

Start by putting it in the dishwasher and dry in your oven @ 170f for 4 hours. I bet there's electrolyte under the ram chips

Tried that too! The board is cleaned, i think there is nothing under RAMs.

 

edit1: I didn't recapped the caps on the bottom side of the board... there are some tantalium cap and others squared, please check the photos!

Edited by hyuma
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10 hours ago, 360alaska said:

No, you only need to replace the electrolytics. Anyhow, looks like a ram problem to me. In my opinion you need to check everything for continuity, pins and traces around the ram.

 

Ok, so only capacitors on top part of the board. I checked the RAM continuity and all seems good. Could be something relate to analog board ?

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Ok, so only capacitors on top part of the board. I checked the RAM continuity and all seems good. Could be something relate to analog board ?

 

I don't think so, if voltages are ok (and they seems to be) i don't see the reason it's your issue.

 

If capacitors have been replaced and are in the right place (ie no inversion in polarity) probably your issue is the Egret (seen this too many times)  the Egret is contaminated by cap goo, and probably shorted.

My solution has always been to remove the Egret, clean underneath and put it back (it's not working a 100 %, but worked for me more than failed)

 

Only trouble, you will need an hot air station and a bit of experience, no way you can remove the Egret without either.

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42 minutes ago, bibilit said:

 

I don't think so, if voltages are ok (and they seems to be) i don't see the reason it's your issue.

 

If capacitors have been replaced and are in the right place (ie no inversion in polarity) probably your issue is the Egret (seen this too many times)  the Egret is contaminated by cap goo, and probably shorted.

My solution has always been to remove the Egret, clean underneath and put it back (it's not working a 100 %, but worked for me more than failed)

 

Only trouble, you will need an hot air station and a bit of experience, no way you can remove the Egret without either.

 

Yes i have hot air station and I've desolder other SMD ICs. Could I check if is shorted in some way before desoldering? I can't find any pinout

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Not really, remove the Egret, clean the board, clean  legs and put it back.

 

Don't use too much solder, i have better results cleaning only the board and legs and soldering back.

 

You can also remove U11 (next to it in the picture) from the picture both are contaminated by nearby capacitors

 

R6UPgh4.jpeg

Edited by bibilit
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2 hours ago, bibilit said:

Not really, remove the Egret, clean the board, clean  legs and put it back.

 

Don't use too much solder, i have better results cleaning only the board and legs and soldering back.

 

You can also remove U11 (next to it in the picture) from the picture both are contaminated by nearby capacitors

 

 

Thanks for your suggestion! Today i removed 15 ICs, please check photos in the link. I cleaned the area of these ICs: 

U20, U21, U13, U14, U17, U18, U6, U7, U4, U4, U3, U2, U1, U15, U12 and U10

 

https://imgur.com/a/Vg4lJhH

 

and seems like there is a bit of life:

 

https://imgur.com/a/eqczefH

 

In this video i pressed reset after a bit and there are like "moving dots" on screen!

Edited by hyuma
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If pads lifted, you need to go to each one and check if the connections are intact from both ends with a multimeter.

 

I got a Mute Classic II, which I recapped years ago. It had the jail bars, then the grey screen then on checking the connections of the lifted pads, I ran a couple short wires to remake the connections. Then it turned on but with no "BONG!" The Cap Goo ate up a lot of the traces from the Audio Section. It's fixable but I had not had the time to fix it but at least I got it to work and boot to desktop!

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7 hours ago, bibilit said:

The Egret is pretty tricky.

 

in several boards i have done the process several times to get it going (ie, lifting and soldering back)

 

The other chip that can be troublesome is the DFAC (U4) sound chip, 

 

Yeah i've desoldered U4 too. There is some troubleshooting manual to check signals, etc...? I really would like to make as many test as possible.

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