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What the problem with my Macintosh ED (512k)?

monoxrom

Member
Hello all!
I have old macintosh and want to fix it

This is Macintosh ED (512k) with 1 meg of ram and SCSI upgrade

When i turn it on i have this:


My board:


I have originals ROM chips but with them i have the same artefacts on screen :( With this chips i try to use another rom what i was found in internet
Some times i have another artefacts but nothing else

Maybe anybody know what is the problem with my Mac? Maybe problems with RAM? How i can check it?
 

bdurbrow

Well-known member
The processor is not running; got hung in ROM before it could initialize the RAM, or can’t write to RAM for some reason. That pattern is what the contents of RAM looks like when power is first applied after being turned off for a while.
 

monoxrom

Member
hmm sad news(
How i can change all this memory to 1 mb simm30 module? (because I can't make two layers of memory chips, like in this version) Maybe some instruction is present on internet?
 

bdurbrow

Well-known member
That logic board has no memory expansion sockets. The few memory expansions that were available are pretty major modifications to the machine; all involved de-soldering the 68000 CPU and putting a special board in it’s place. That board would have a 68000 (usually new), PALs for doing address decoding, and the memory chips themselves. This was only done by 3rd party companies, and always voided Apple’s warranty on the machine.

Apple’s solution at the time for upgrading the computer was “Buy a Mac Plus”.

Because of this, I doubt that you’re going to find one that isn’t already installed into a logic board.

But before you even consider that, you need to get the machine working. Unless something has changed since your first post, nothing useful is going on when you turn on the power.

If you’re not familiar with electronics troubleshooting at the chip level, using tools like an oscilloscope and logic analyzer; I would strongly recommend that you take it to somebody who does this frequently on vintage Macs and knows exactly what they are doing. This Mac is rather rare and valuable nowadays, and you don’t want to be trying to learn how to do this kind of work on it. For learning, get a semi-old device of some sort that nobody cares about (VCR, or perhaps a radio) and practice on that… so when you do damage it (and everybody does while learning) it won’t be a big deal.
 

monoxrom

Member
Ok how i can make 512 kb of ram? Because i can replace chips and i was do this few time on another computers
but i can't make two layers of chips like now present on board
 

mg.man

Well-known member
I suggest you try removing that add-on board - which is there to give you SCSI - you don't need it while you're debugging the boot process. Just put the ROMs directly into the logic board sockets and see if the machine will boot or if the behavior changes. Also - has this machine ever booted correctly? And, where are you located?
 

monoxrom

Member
First time i was reed my ROM chips and found some garbage in one chip. Another one looks good
I was write new ROM (two chips) from here:
https://github.com/Stephen-Arsenault/MacRoms
(UK Mac Plus)

Ysterday i was try to turn on my Mac without SCSI board and i can't boot and I saw nothing
Only some clicking sounds from speaker and near 1-2 volts at +5 volts line

Today i turn on my mac and it works!

My starting video:

What i need to do now? replace all caps at power board? but they looks normal not flow and did not swell as i see
------
I'm from Ukraine, sorry for my English :)
 

cheesestraws

Well-known member
I'm from Ukraine, sorry for my English :)

Your English is fine, don't worry :) . Your communication is clear and understandable.

but they looks normal not flow and did not swell as i see

Caps can fail in ways that aren't visible from the outside. Specifically, they have a liquid inside them, and if they dry out, that is also a problem. The power supplies in those computers get very warm, which in the long term is bad for the capacitors especially (but all the other components as well). So even if they look OK, it's probably wise to replace them anyway.

That said, it might not be the problem here. Was the day it worked noticeable colder or warmer than the day it didn't? Another thing those boards suffer from is bad solder joints, which can contract and expand with temperature and cause weird and incomprehensible issues. Might be worth trying to turn it on sometimes for the next few days and see if you can work out if it's temperature that's making it act weirdly. (Another option is to very gently warm the board with warm air, or cool it precisely with a freeze spray, to see if you can find the bit that's misbehaving).

These are just ideas, no idea if they're right, but they'd be what I'd check first if I were seeing what you are.
 

monoxrom

Member
I need to check contacts on power board or logic? or both? :)
I have already seen some bad contacts on the power board and soldering them
 

cheesestraws

Well-known member
Power/analogue board. They're famously prone to bad solder joints that are difficult to see. Which is very annoying of them :-(.
 

dochilli

Well-known member
First you need stable voltages at 5 and 12 Volt. Check the voltages. Perhaps you can use an osziloskop to see if the voltages are stable.
Recap the analog board!
 

monoxrom

Member
i was replace all caps on analog board but nothing happen better, all the same

I think i have problem with GND and +5 volt lines, because i have resistance between them
I think I have a damaged some SMD capacitor on board

I think this is not normal have "that" in any of capacitors on board





Or that is normal? i know capacitor must have infinite resistance in one of the combinations of probes.
The problem is that these capacitors have poor markings on the glass, so it is almost invisible :(
Does anyone know the marking of capacitors on these macs?

 

bdurbrow

Well-known member
Resistance between ground and power rails (5v, 12v, etc) is normal: your multimeter is providing a tiny bit of power to the probe tips at a known voltage, measuring how much current flows, and from that figuring out how much resistance must be present using Ohm’s law. That tiny bit of power will flow through all the parts on the board that are connected to the points your probes are touching; and read out as a resistance value.

If you ever get an infinite resistance value; that means that either the circuit is open; or that your meter in it’s resistance mode isn’t providing enough voltage to get over the diode drop of the parts on the board (semiconductors like diodes and transistors won’t conduct any current at all until the voltage gets high enough; usually that voltage is well under a volt). Diode mode on a multimeter applies a somewhat higher voltage and measures what that diode drop voltage is.

And of course; a very low resistance value either means that the board is designed to use a lot of power (Ohm’s law at work again); or something on the board is shorted out.
 
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