Apple II Rev. 4 Motherboard question

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Joined: Oct 9 2013
Posts: 364

Evening all (at least where I am)

I have received several Rev 4 motherboards inside II+ machines in the past few months. The other three I have (one went to Transwarp guy) had the 'Rev 4' under the slot and the 820-0001-04 under the CPU and a 1978 Date silkscreened on the PCB by the CPU and a motherboard Date of 794x and the Memory Select Blocks were soldered.

The machine I just got (S/N in the 7k range) has all the same markings, what looks like a 7940 mobo date (the 79 is very hard to see) but the Memory Select blocks are socketed not soldered.

Everything on this motherboard scream Rev 4 but I have never had a Rev 4 with sockets for the Memory Select Blocks. This a common thing or perhaps a modification/repair?
Just curious since I have had several other boards from the same era with the same markings (thanks to you guys teaching me what was what!) and this one is different in that one respect.

I was under the (apparently wrong) impression that Rev. 3 boards were the last to have sockets for the Mem Select blocks and Rev 4 was soldered and they disappeared entirely after that.

I will get pictures up shortly, came in to post this and get photos and the wife informed me my dinner is getting cold!
Zan

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Joined: Oct 9 2013
Posts: 364
Re: Apple II Rev. 4 Motherboard question

OK, added photos to the original post. This machine has had some mods done to it. There is an EMI shield across the back that was definitely added later. The case snaps were drilled (as was the case) and they were screwed down with flat head screws similar to the later RFI machines that had the snaps riveted. There was/is a video card that came with it and as can be seen in the photos it is attached to the post next to the game port. The video card had a composite to BNC cable with it but I am unfamiliar with the wire running to the post next to the game port.

I have not tested the machine yet as I have not cleaned it nor have I removed and reseated all the ICs yet.

Just had not personally seen a Rev 4 with socketed mem select blocks so wanted to know what others experiences were.

Thanks,
Zan

speedyG's picture
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Joined: Nov 16 2011
Posts: 2376
Re: Apple II Rev. 4 Motherboard question

Hello Zan8675,

nice pictures.....

remarkable is the slight variation of the 40 col / 80 col switch at the "prototype"area
added to the card.....
instead of picking the 40 col from the regular pickup point of the additional videoconnector
it picks up the summary signal upfront of the summarizing transistor
and second it seems to pick up the switching signal from the card instead of from the
mainboard like in most general mods ( videx 80col switch ).

FIY the sketch below:

sincerely speedyG

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Re: Apple II Rev. 4 Motherboard question

speedy, I had never seen that before and since I have yet to test the machine could only assume it was to push the video to the card (like a jumper wire from the video out to the switch plate of a Videx card)

Any thoughts on the motherboard? While there's obviously a whole lot I don't know and have not seen, i had not seen a socketed memory select block on a rev 4.
Knowing so many others on here have or have had different revisions I figured someone here may have seen the same thing (or has one)

Today I will be taking the machine apart and cleaning it.

I have added 8 photos to the original post that are closeups of the modded area on the board and the video card itself.
The last 8 attached photos.
Zan

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Joined: Jul 6 2009
Posts: 44
Re: Apple II Rev. 4 Motherboard question

Hello

I have Apple II Plus #3207 - motherboard is Rev.4 has a datecode 7930 and the memory blocks are soldered.

Stefan

PS Somewhere I have another board I saved from scrap - rev.4, datecode 80XX if I remember. Will try to dig it out and check memory blocks

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Re: Apple II Rev. 4 Motherboard question

Hello Zan,
after i now had the chance to see the topside i must confirm:
this is really a very rare mod.
I haven´t seen anything similar before.
unfortunaly one of my teeth decided to pass away this evening to the fairyground of the
toothheaven. So my concentration is disturbed quite a bit by aches....
hope tommorow the aches have passed by and concentration turns back.
The pictures of the mod are absolute perfect so i can analyze tommorow
all aspects of the mod that is quite far more sophisticated than i expected.
I´ll then turn back here with details explained also by the circuitplans....
I wish you a nice evening remaining till tormmorow sincerely
SpeedyG

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Re: Apple II Rev. 4 Motherboard question

Ouch, tooth issues can bring the biggest man to his knees!

The card acts as a typical Videx clone with Ctrl-A switching between lowercase and uppercase but, unlike a Videoterm or Ultraterm, in lower case the Shift key works as you would expect on a typewriter or modern computer allowing upper case while depressed and back to lower case when released. Interestingly, like a shift key mod all the shift characters work as normal except the @ and ^ keys (on the P and N keys respectively) which you need to switch back to upper case to get those Shift characters.

The video works as expected, 40 column upon boot and switching to 80 column w/a PR#3.

I have not done any further testing yet but so far this is a nice little II+ with some twists.

As Stefan said, his Rev 4 is soldered, I'd love to see if we can find some other Rev 4 boards that are socketed. Always interests me when you think you knew something
and find out you didn't know what you thought you knew! Smile
Zan

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Re: Apple II Rev. 4 Motherboard question

Hello Zan,
just short feedback before the day ends...:
analysis will request another more day.....
fighting some issues:
1st issue: i have a manual from videx videoterm card with circuitplan...
- but it´s protected by masterpassword and therefor it´s not that far possible
to extract part of the circuitplan for this analysis that simple....
i managed to handle that issue, but the solution results to graphic
with very bad resulution....
and 2nd issue at the other hand i´m also involved in the moment in another task that has a limited deadline;
so can´t work the entire day at this task and must solve the other task in the given timeline...
so my time in this task is at the moment pretty limited till the other task is solved...
speedyG

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Re: Apple II Rev. 4 Motherboard question

Speedy, please don't rush. While certainly interesting and great to get more info on a perhaps unique mod (and more importantly to document it for archival purposes)
my main issue was with the memory select blocks being socketed on a Rev 4 board. The fact that there was something different/interesting about the machine beyond that is a bonus from my perspective.

I'm still wondering what other Rev 4 boards out there are like this one when I have had 3 others that were soldered and at least one other member has as well.

I started dismantling the system and cleaning it. A number of chips on the motherboard were marked with "white out" (not likely from then, but some form of pink and on some white dabs in the corner of the ICs) I did not see how well that can be seen in my photos but now that the case is off I will take closeups of the whole motherboard. I'd like your thought on it. I also found a tag (hand written label) on the inside on the baseplate. One said "Videx Inverse OK" and the other (which had come loose from the base plate...glue was old) The other was something like "Videx Boot OK" but I do not know where it had been afixed to the base plate since it came loose.

Again, I will post detailed photos tonight. The marked chips in the given sockets seem to be the correct ones (not like they were substitutes) but I have not finished removing all of them and checking date codes either.

Some interesting stuff here for sure. Perhaps they were simply chips that were marked as the ones that were replaced, I have no idea.
Zan

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Re: Apple II Rev. 4 Motherboard question

Hello Zan,
i´d need some picture about the solderingpads below of the aluminium cased transistor
close to the videoplug on the card and at least a view that displays how that transistor
is soldered to the card ( enabling me to identify E B and C of the transistors and
kind of transistor.
sincerely speedyG

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In early days I had a lot of money but no time - now I have no money but a lot of time....
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Re: Apple II Rev. 4 Motherboard question

I did check the second rev.4 motherboard I have. It has datecode 8017 and memory blocks are also soldered.

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Re: Apple II Rev. 4 Motherboard question

Stefan, thank you very much for checking. Hoping to hear from some other members. Thanks again!

Speedy, I added three photos to the original post (last three photos)

I got the front pretty well (assuming I took pictures of the correct areas) but the back gave me problems so I had my son use his camera to get a closeup of the back.
Very large photo but it should show what you need.
Zan

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Re: Apple II Rev. 4 Motherboard question

Hello Zan, sorry - seems i did not explain correct....
the 2 pictures display the topview to that transistor
( like the previous pictures too ) so i can´t view
anything about the legs of the transistor between the transistor and the PCB....
45 degree angle view to that area below of the transistor is what i am missing....
speedyG

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In early days I had a lot of money but no time - now I have no money but a lot of time....
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Re: Apple II Rev. 4 Motherboard question

Gotcha. I'll get that today.
Zan

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Re: Apple II Rev. 4 Motherboard question

Have a 7949 and a 8008 with soldered memory blocks.

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Re: Apple II Rev. 4 Motherboard question

Wayne, thanks. While not earth shattering, I just was curious if anyone else had a Rev 4 with socketed mem blocks.
This machine had RFI work on it (paint on inside of case, shield on back, strips on lid) that I am fairly certain were not indigenous to this early a II+ (I could be wrong, but never saw them on any other early II+ I have had or still have)

The motherboard mod, homemade video card, this is a fun machine to mess with!
Zan

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Re: Apple II Rev. 4 Motherboard question

speedy, I added two more photos. Hopefully I got the ones you need this time.
Zan

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Re: Apple II Rev. 4 Motherboard question

Hello Zan,
each of them works perfect as "missing link" and displays the legs of that transistor.
both enable to proceed with analysis.
thanks a lot
speedyG

__________________

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....