Mac Plus Sad Mac Repair

[Antoshig]

I purchased a Mac plus online from someone for a few bucks because it wasn’t working, so I decided to repair it myself plus it would be a great opportunity to learn about computers since I am pursuing in that field. I am having trouble with it.

Symptoms:

At startup the chime sound comes on, but I get a sad mac icon with a checksum of 0101A0 with some morse code on the bottom.

Steps I took to try and solve the issue:

I looked it up and it’s a ROM test failure.

I tried resoldered the ROM sockets, but with no avail.

I also tried replacing the simms with new ones, still didn't work.

I checked the voltage coming from the power supply they were all good.

I did more research about ROM’s and found out you could read the data and analyse with some ROM images from the internet to see the integrity of the data. In order to read the ROM, I would need a EPROM programmer which I don’t have.

I need help in fixing the Mac Plus. I'll put some picture for reference.

It's my first time posting on this Forum. 

Thank you  

 

[drybones99]

I once had a problem where the computer would freeze randomly, and garbage would appear on the screen. Often, I would even get jail bars on the screen on startup, with no chime. I fixed the problem by removing the ROM Chips from their sockets, and brushing both sides of the pins with sandpaper (A toothbrush might work as well, but sandpaper is recommended). I put them back in, and the computer has never frozen or given me jail bars again. If your chips have green residue on the side, then that should be your problem, as it is corrosion. Using this method removes the corrosion, and should make the pins a solid silver color that shines.

If that doesn't work, you could try checking the voltages coming from the ROM Chips themselves, and comparing them with what they should be on the data sheets, if there are any.

 

[mraroid]

I am impressed at how clean you gotten your board.  I see a can of what I suspect is some kind of cleaner in photos.  What did you do?
 
I saw a video on YouTube a few years ago where I guy sprayed contact cleaner all over his motherboard.  Then he used a *elecrtric* tooth brugh to do the actuall cleaning.  After that a second spray of contact cleaner and then compressed air to dry.  It came out spotless. 
 
 What ever your methoid you used,  is is a great job.  One can tell you take pride in your work. Keep us updated.
 
jack

 

[Antoshig]

drybones99I sanded down the rom pins just like you said even though my roms weren't corroded and still hasn't solved the issue

I don't have an extender for the power cable coming from the Analog Board so it would be difficult for me to test the voltages outside the case. Maybe if I disassemble the Mac Plus from the case. But I doubt it's the voltage. I tested the leads on the external scsi port and I get the right voltages same as in LARRY PINA's BOOK. 

and 

mraroid
The inside of the Macintosh Plus was in good shape apart from the dust. I vacuumed out the LogicBoard and the AnalogBoard then I cleaned it with contact cleaner. I sprayed it on a Q-tip and worked my way in between the chips. I didn't want to do clean it with a Dishwasher, because I am scared to drown it in water and damage the PCB. 

I was thinking to buy the Mac Rom-inator from BMOW as a replacement for the Rom I have now. I want to be certain it's the Rom before I make my decision to buy the kit. 

Thank you for the reply guys. I will try every possible method to try and fix the issue so keep the posts coming. I'm all ears.

 

[bigmessowires]

I'd be happy to sell you a ROM-inator kit, but I'm sort of dubious it would fix your problem. I'd wager you're more likely to have a problem with the traces on the logic board, or with the rom sockets, or maybe with the parts that do address decoding. I think it's kind of rare that the actual ROM chips go bad. But if you want to try and see, just let me know.

I might suggest grabbing a copy of the Plus logic board schematic, and using a meter to check for shorts or opens on all the pins of the rom sockets. Maybe also check the connections between the CPU and the address decoder stuff. 

If you're game for a project and comfortable using something like an Arduino or Raspberry Pi, you could also build a little jig to read the contents of the ROMs, and confirm whether they match the known contents that should be in there. The rom pinouts can be found in the Plus schematics. It's just a basic ROM: set the address lines, read the data lines, repeat 128K times.

 

[Antoshig]

I'd be happy to sell you a ROM-inator kit, but I'm sort of dubious it would fix your problem. I'd wager you're more likely to have a problem with the traces on the logic board, or with the rom sockets, or maybe with the parts that do address decoding. I think it's kind of rare that the actual ROM chips go bad. But if you want to try and see, just let me know.

I might suggest grabbing a copy of the Plus logic board schematic, and using a meter to check for shorts or opens on all the pins of the rom sockets. Maybe also check the connections between the CPU and the address decoder stuff. 

If you're game for a project and comfortable using something like an Arduino or Raspberry Pi, you could also build a little jig to read the contents of the ROMs, and confirm whether they match the known contents that should be in there. The rom pinouts can be found in the Plus schematics. It's just a basic ROM: set the address lines, read the data lines, repeat 128K times.

I have both the Arduino Mega and a Raspberry Pi B. I am not a good coder, does anyone have a programme I can upload on the Arduino or Raspberry? I can do the wiring but I just need the schematic as well. 

 

[bigmessowires]

Maybe try this: http://www.nycresistor.com/2012/07/07/stick-a-straw-in-its-brain-and-suck-how-to-read-a-rom/

 

[techknight]

Only 1 case I have ever seen a ROM bad, and it was in an SE..