Mac 128k help needed!

[Elfen]

Interesting. If it were an SE/30, it would be a RAM or broken trace issue. But since this is intermittent.... Hmmm... Page 65 of Dead Mac Scrolls says its a ROM Issue, probably after an upgrade.

Take out the board and with a chip remover or pencil and small flat head screw driver, loosen the ROMs and IWM chips (next to the ROM, if it is in a socket), wiggle them on the sockets and gently press them back in.

If it continues, then there is corrosion on the chips' pins. Remove the ROMs one and a time and with very fine Emory cloth, not Sandpaper - ask your hardware store for Emory Cloth, they know what it is, polish up the pins on the chips on both sides - the outside of the chip and the inside. Be gentle doing this so you don't bend a pin(s). Put ROM back in socket and do the other ROM and then the IWM Chip last.

After many years, sometimes the connections corrode over time and need to be cleaned up.

 

[KenB123]

Yes I have already cleaned the pins with a wire brush and gently brushed them.

The iwm isn't socketed.

I will try a set of roms From another board but I am pretty sure I tried that already.

I will let you know the results when I get home from school.

Thanks!

 

[Elfen]

Look at:  https://68kmla.org/forums/index.php?/topic/23844-mac-plus-temporary-jailbar-screen/

Sounds to me like your Mac is not reaching its required voltage. Its either a part on the analog board or the caps going bad on the logic board, which is rare for a 128K. I forget which pins it is, maybe Uniserver or TechKight can post it, but you can check the voltage on the floppy port on the back of the Mac. If it registers less than 5.0 volts, you could get to the analog board and turn the potentiometer/variable resistor for 5 volts. Turn it a bit while it is off, turn on the machine and give it a while to come up and measure again. Turn off and adjust again as needed. It is better to be a bit over 5 volts, like 5.1 volts on your digital multimeter or the needle a tiny bit past the 5 volts mark on the analog meter. I use both.

If you still have this problem after adjusting, then its time to look at the analog board or the caps on the logic board.

 

[KenB123]

I have already tried to adjust the voltage on the pot but no dice.

Sorry it's been so long since I posted on here I have lost steam on these things

But give me a few days and I'll get working on them again!

 

[Elfen]

Time to get out the multimeter and start checking traces. With the exception of maybe 4 lines, all the lines on the 4264 RAM Chips are connected to their neighboring chips in parallel. So all the first row chips are connected together and all the second row chips are connected together and a majority of chips in Row 1 and Row 2 are connected to together. 

This diagram shows that all but 2 or 4 pins should be connected together. Pins 2 (Data In), and 14 (Data out), with possibly Pins 4 (/RAS), and 15 (/CAS) should not be connected together. All the other pins should be connected. When they check out OK, follow the traces to the connected chips and test their connections with the multimeter. They should be OK. 

Other than that, the only thing to do is to test the actual chips outside of RAM. I would guess following the suspected RAM Chip Data In/Out Lines to where they go and check their traces. If OK then those chips might be at fault. Without an oscilloscope it is hard to determine. Only Uniserver and/or TechKnight would be able to help out at this point.

 

[KenB123]

Alright everyone I got the took in the mail today and it worked great! Well until I tried to remove the chip. The holes looked clear and has nothing in them but I couldn't get it out. So I took a Dremel and just cut the legs off of the chip. And then I desoldered everything individually.

Everything looked really nice

I didn't get any new chips from my friend yet so I decided to use some chips off of another dead 128 board. Since I didn't know the state of the chips that I removed I used a socket I plugged in a chip and it gave me a really weird chime. And then gave me this...

So I'm assuming I either need to get a known good ram chip or just scrap it now.

Thanks for any advice!

 

[KenB123]

 

[Quadraman]

I've seen the non-Apple branded RAM chips for sale cheaper than what you have found them for BUT the electronics supply houses that I have seen them for sale in all have a minimum order requirement. I would have had to have bought dozens of them to meet the minimum and I have no use for that many. I found a 128k board on ebay Australia that had the RAM chips removed because at one point the owner wanted to do a homebrew 512k upgrade but never got around to it. I got the board and the original chips in a plastic bag shipped from New Zealand for like $100 and if you've seen shipping charges from Australia/NZ and what a complete 128k motherboard normally sells for you know that's cheap. 

 

[KenB123]

Oh wow that's a really good deal! I'm glad you were able to get that board working with all original chips!

Uniserver agreed to send me 20 chips for $25 including shipping.

I hope new chips will fix this boards issues.

 

[Mac In France]

Hi !

Just to add that the SAD MAC code 2 = Memory test - bus subtest

I think that adding a socket changes resistance, so you have to do it everywhere for the 16 chips. That may change voltage.....

Do you found a solution?

....

As I'm starting to do the same thing (one chip F5 is bad = error 04001) I have a decision to take, but I do not have the information needed:

My motherboard is a 128 second generation (design was the same as 512) only ram chips AND another chip AS253.

But I did not find any listing to be sure that all is correct..

Is there anyone knowing what to do for this upgrade?

My actual check list is:

Change 16 chips RAM

Add 1 chip AS253

Add 3 resist. R41,R41,R42

Add 1 C 51

Cut the W1

Is that anything?

Thanks a lot

PS: design of this  card is 128K :630-0101  -  512K : 630-0118