Help revive an Original Macintosh Prototype

[North Hedge Ned]

Hi everyone - this is an off shoot from my previous post entitled "Different Macintosh in Original User Guide?" because it now tries to tackle the issue of getting the second of my two Original Macintosh prototypes working.  Here is the issue:

Unit powers on, beeps ok, but the video comes up all weird.  Upon closer inspection, I see that two items (resistors, converters, something weird) are slightly cracked like dried honey at locations C37 and C38 of the power sweep board.  Likely the cause?  There are a slew of photos for you all to see - what do you think?  See anything else?

I have tried ALL available video adjustments to no resolve - voltage, focus, vertical horizontal, even the two other adjustments for brightness and such - nothing.

Any help in evaluation would be much appreciated.

 

[North Hedge Ned]

Even the same circuit at C33 has slight cracking on it too...  Not sure what these do.

 

[AwkwardPotato]

C33, C37, and C38 all appear to be RIFA line filter capacitors, and those don't affect the operation of the computer when they fail.

 

[AwkwardPotato]

For starters, resoldering the joints on the flyback transformer and all of the connectors might help.

 

[LaPorta]

Just as AP said. Next, check the other caps as best you can. You can also look at the plastic sheet that normally covers the side of the board: look for any obvious burn marks, which could indicate a short or overheating.

 

[Trash80toHP_Mini]

Fabulous set of pictures. Is this A/B identical to the board in the working example? If so, that should help in electrical diagnostics if you need to to take it that far. Nice to have a control for testing if the boards differ significantly from later production versions. Have you swapped logic board or A/B with the working example to isolate the fault to one or the other component? Looks like A/B, but Logic Board components could be a problem?

Linkage to original thread: different-macintosh-in-original-user-guide

On a side note, that "heat spreader" fence looks more like an example of "just in case" RFI shielding for Class B certification, not a heat shield for the vents. The RFI shielding "fence" at the backplane persisted through SE/30. Were the components arrayed across the top edge buried farther down (in the case) on the A/B in later revisions?

 

[North Hedge Ned]

C33, C37, and C38 all appear to be RIFA line filter capacitors, and those don't affect the operation of the computer when they fail.

Interesting, AwkwardPotato... I wonder this though, because last night in testing an odd thing happened to my Mac Plus.  Ran the Plus a couple of times ok.  Then, the Power was off, AC cord in, and an external SCSI HD 80SC was connected and running.  Then I heard a loud sizzling, and then a burnt popcorn smell.  When I inspected inside, I found one of these very filter caps you speak of, but it was literally cracked apart, freshly, and the smell was the strongest at that point.  I am scared to turn it back on now.

I guess the question is - where can I find replacement RIFA line filter caps?

 

[North Hedge Ned]

Fabulous set of pictures. Is this A/B identical to the board in the working example? If so, that should help in electrical diagnostics if you need to to take it that far. Nice to have a control for testing if the boards differ significantly from later production versions. Have you swapped logic board or A/B with the working example to isolate the fault to one or the other components. Looks like A/B, but Logic Board components could be a problem?

Linkage to original thread: different-macintosh-in-original-user-guide

On a side note, that "heat spreader" fence looks more like an example of "just in case" RFI shielding for Class B certification, not a heat shield for the vents. The RFI shielding "fence" at the backplane persisted through SE/30. Were those components moved farther down on the A/B in later revisions?

Trash, I would have to check.  Since the one unit is working, I really don't want to run the chance of screwing up any good components on it.  Actually strongly thinking of putting it on the market (there is a whole different thread I am sure).  Don't want to run the chance of 2 bad units.  LaPorta, and AwkwardPotato - thanks for the starting points.  May be a silly question, but do I have to discharge the CRT before soldering the FB Transformer?  That is one tool that I do not have - a CRT discharge tool.

 

[bibilit]

Those RIFA capacitors are prone to failure, but otherwise pretty easy to replace and when they fail, apart from the strong smell, won't harm anything.

Still available and cheap.

 

[AwkwardPotato]

When I inspected inside, I found one of these very filter caps you speak of, but it was literally cracked apart, freshly, and the smell was the strongest at that point.  I am scared to turn it back on now.

I guess the question is - where can I find replacement RIFA line filter caps?

You can probably remove the filter cap for testing, but definitely plan on replacing it. Replacements for these can be found on mouser.com or other electronics distributors. One thing to keep in mind: there are two different kinds of line filter caps in Compact Macs: X2 and Y2, and you need to replace like for like; e.g. can't replace an X2 with a Y2. They should be marked on the top/side with what type they are.

May be a silly question, but do I have to discharge the CRT before soldering the FB Transformer?  That is one tool that I do not have - a CRT discharge tool.

Yes, definitely discharge the CRT before doing any work on the analog board.

 

[North Hedge Ned]

Awkward - and what about other factors?  I went on Mouser.ca here in Canada, and they have a lot to look at.  Voltages and all the likes.

 

[AwkwardPotato]

"X2" basically is the voltage rating, so you can just look up "x2 capacitor," choose "Safety Capacitors," and then pick the options "Radial" and "Safety Film Capacitors." Pick a part with the same capacitance (measured in F, farads) as the damaged one (should be written somewhere on the cap), and make sure to get one with leads spaced roughly the same width as the one in the Plus. I'd also check the datasheet for the part you find just to make sure it is an X2-rated part.

 

[North Hedge Ned]

"X2" basically is the voltage rating, so you can just look up "x2 capacitor," choose "Safety Capacitors," and then pick the options "Radial" and "Safety Film Capacitors." Pick a part with the same capacitance (measured in F, farads) as the damaged one (should be written somewhere on the cap), and make sure to get one with leads spaced roughly the same width as the one in the Plus. I'd also check the datasheet for the part you find just to make sure it is an X2-rated part.

Awesome AP - thanks.  The Plus has only X on it - no X2, same as the 128K Prototype - all X on the bigger ones, and only Y on the smaller ones.  I will find these once I get some time - right now getting units that work out of my collection ready and for sale.

 

[North Hedge Ned]

Hi everyone - still have not had a chance to dive into the repairs - time and money are both short right now.  Anyone in the Ontario, Canada area who may want to lend a hand with their know how?  As for the working 128 Prototype, I did find out some more specifics - actually both of them - working and on-working:  They are both units with the #6 logic boards as per Folklore, by the identifier of the Mr. Macintosh all over the place, and part 820-0086-0 - made in May 1983.

I am in current conversation with one of the original designers now to gain more information and insight.  To my understanding, this is the only era with the Mr. Macintosh.  My photo's must have been just after Apple abandoned the Twiggy prototype.  This is what I want to confirm.

Lastly, then, I wish to sell the working one now.  Before I unleash it on eBay, which might cause a frenzy, anyone here interested, have the money, and is interested?  This unit would be next-in-line to that Twiggy version that is all over the web.  Thought that I would do the respect of asking here first.  $10K US - am I nuts?

 

[North Hedge Ned]

For the original post and more pix of the unit

 

[North Hedge Ned]

Hi everyone - the story still is unfolding on this and the other unit that I have - truly Prototypes as most of you confirmed - for sure.  They have 512K RAM, to boot!  I have a question though.  Two actually:  Could anyone tell me what to use and how to read the serial number from the logic board like the modern System Profiler?  I want to know what serial number can be pulled from the logic.  Secondly, is there a software that I can run on the unit that will copy the ROM 7.0 off the daughter card?  I would like to be able to have the ROM locked in time and preserved.  Thanks in advance.

 

[Dog Cow]

Could anyone tell me what to use and how to read the serial number from the logic board like the modern System Profiler?  I want to know what serial number can be pulled from the logic. 

None.

Secondly, is there a software that I can run on the unit that will copy the ROM 7.0 off the daughter card?  I would like to be able to have the ROM locked in time and preserved.  Thanks in advance.

ROM 7.0 is the shipping version of the original 64K ROM. It's not a prototype ROM. But you can double-check it with MacsBug. Enter DM 400000 and report back what the first line reads. You should get a version number and checksum byte that will identify the ROM.

 

[LaPorta]

You can use CopyROM from Paul Pratt, the guy who made minivMac. A copy of it should be available on his site.

https://www.gryphel.com/c/minivmac/extras/copyroms/index.html

If it is an early ROM version, it would be neat to use that with the 128k minivMac and see if there are any differences.

 

[North Hedge Ned]

None.

ROM 7.0 is the shipping version of the original 64K ROM. It's not a prototype ROM. But you can double-check it with MacsBug. Enter DM 400000 and report back what the first line reads. You should get a version number and checksum byte that will identify the ROM.

Dog Cow - thanks for the info.  Now to really get together some old Mac's and 400K floppies!  Have to get MacsBugs installed on one with a system.  Maybe too, I can boot from the internal floppy with the system I have, then run an external floppy with MacsBugs, and CopyROM (thanks @LaPorta) for that link.

Below are photos of each of the 512K adapter board that is on the logic board of these units.  Any clues here without running MacsBugs?