Mimeo 1 Build - Problems with blowing fuses

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Joined: Oct 4 2014
Posts: 64
Re: Mimeo 1 Build - Problems with blowing fuses

speedyG wrote:

Hello Sherlock,

like explained in a former posting several months ago, the
bunch of us guys building replicas split into two different groups:

a) those who want to get a complete as possible similar setup like at the original
( looking for correct dates codes, correct TI sockets and so on... )
i for example belong to this group...

b) those who want to build a replica for extended working playing with the PCB
and who insist in durability and clean operation selecting as reliable as possible
sockets and parts.... ( prefereably new ones that are not that far aged.... )

The pictures you have published makes me think, that you belong to the second group,
because the former Apple-1 has never been equipped with modern precesion sockets....
May be you´ll spend some time at the Apple-1 pages within my site to view the differences...

so if you prefer first to have a reliable operating board you´d prefer the second group but still have the option
to switch step by step to the first group... though that will cause a lot more of difficult work ...
specially changing sockets is far too much work and risky, because traces might become damaged while
running such procedure....

but a simple switch between different kinds of diodes used in the rectifying brdge is not that
difficult change ....

at least i´m happy that the pages have been usefull....


Speedy, I belong to the second group as well, with most of my parts dating to 1978.
It best to start off in the second group and experience a working board before spending money for perfect date matching parts to be in the first group.
Then I would start another board for group 1.

The original TI sockets in the Apple I were very unreliable and start becoming intermittent after a few pulls and reinsertions.
Machine sockets are definitely the way to go for a group 2 board.

When I decide to go to group 1, I will pretest all my ICs on my group 2 board to minimize insertions/removals.

speedyG's picture
Joined: Nov 16 2011
Posts: 2376
Re: Mimeo 1 Build - Problems with blowing fuses

Hello IEEE802,

well i started immediatly 2 years ago with group 1 and it took me nearly up 1 1/2 years till i was able to
perform first testings at the board..... and in fact i even was crazy enough to also immediatly start making
replicas from both versions of the Apple-1 ( the "pre-NTI" board = MIMEO and the "NTI"version of the board
that was manufactured later =NTI Newton ) and i even took care while populating to make sure, that at my 2
replicas there are the same differences visible, that are also visible at the original ones.

You can view that aspects at my pages related to the topic:

And i won´t tell the story about the run for that parts here... it would crack limits of a single posting....
some part of the story is mentioned at the pages mentioned above....
also not to talk about the cost....

but watching the market of that parts now just few months ( or better about 1 year ) later i must state that
in the meantime it´s nearly impossible to get in touch with correct sockets or several other parts....
and even the parts availiable the prices have been rising like a saturn 5 from Cap Canaveral....
Nowadays there would be no chance ( at least for me ) to afford the amount of money demanded
in this days for that parts...

Just an advice at the moment for both of you Sherlock and IEEE-802:
The picture of the rocket is also valid to the availiable early Apple ][ keyboards....
3 years ago it was possible ( with some luck ) to get in touch of such a keyboard
at price of 50 to 70 U.S. Dollars.....

In the meantime that has "rocketed up" to an amount far above 100 Bucks...
Last year i therefor have given advice to hunt for a cheap Apple ][ clone from
Taiwan ( entire system less than 100 bucks and then just use the keyboard from such system
and besides having some bunch of spare chips for the Apple II on the shelf.....

Maybe - ( quite several months back ) Mike Willegal intended to make a run for copies of the
early datanetics keyboard PCB .... but that project got shot off the tasklist due to the
fact, that that needed old keyboard encoder chips are not availiable anymore....

Besides - in my site there are also some DIY projects related to make an own simple
ASCII keyboard, that would fit with the Apple 1 with very minor changes...
and the keyboard switches from the very early IBM PC keyboard are quite usable
for such a project... such keyboards are still in reach at the junkyard or recycling yards...
( just bear in mind in that old days you could kill a person by slaming such an old fashioned keyboard on the head .....)
they are nearly undestroyable....

so good luck with your search for a keyboard...
(Just another hint: very old teletype machines also had such simple ASCII keyboards )


In early days I had a lot of money but no time - now I have no money but a lot of time....
the second part includes less friends but a lot more joy on life....

Sherlock's picture
Joined: Dec 20 2014
Posts: 135
Re: Mimeo 1 Build - Problems with blowing fuses


So I removed all the A14F diodes, and replaced them with 1N5400 diodes. I rested the +12/-12/-5V power lines, and it worked fine like before. I disconnected those power lines, and connected the transformer with the replaced diodes, and IT WORKS! My regulated +5V line is humming smoothly.

I replaced the other power lines, and now all the power lines are working as expected!

Thank goodness! Thank you everyone for helping me fix this problem. I'd never have figured it out by myself.

Now onward to populating the video ICs and hopefully beyond. Thanks again!

speedy: yeah, I'm not even thinking too much about the keyboard yet. I got the PS/2 adapter so I can test with a common keyboard. I'll keep my eyes open, but probably won't get anything until I have the machine working. The prices are high, but I guess they're not making any more!