Info on RAM and PDS cards

[Sideburn]

Anyone have some details on what these cards might be? I know one is RAM but what are the others and how much RAM?

I dint have them in my possession yet to try them or take better photos but will soon.

 

[SuperSVGA]

The first card is just 1MB, the second looks like probably 6MB.

 

[Sideburn]

The first card is just 1MB, the second looks like probably 6MB.

Ahh 2 RAM, Any idea what that other card is with what looks to be a green POT or transformer on top right?

 

[SuperSVGA]

That would be a modem, not sure which one as it doesn't look like the standard Apple ones.

 

[Sideburn]

That would be a modem, not sure which one as it doesn't look like the standard Apple ones.

Ahh thats what I thought at first but didn't think there was an opening on the case for the jack.

 

[Sideburn]

I got the cards in today. The modem works and the 1MB official Apple RAM card shows up in the finder with a total of 2MB but the other card is not showing up in the finder. I assume it should without the need of any third party drivers or software correct?

That would be this card:

 

[SuperSVGA]

That's correct, it shouldn't need anything special. Either there's a fault on the card or something else is preventing it from being added as valid memory.

I'm not sure if it's just the picture, but that's a very sketchy looking bodge running over that chip. Did someone try to modify the address decoding?

 

[Sideburn]

I noticed that too. No idea it arrived that way.

 

[SuperSVGA]

I can't tell from the picture, is that the 74AC138 that the bodge is on? If part of the RAM on the card is disabled it may change the card's start address, which would could be why it's not working.

 

[Sideburn]

 

[Sideburn]

The lead is also cut off the chip

 

[SuperSVGA]

Well I can't tell for sure since some traces are either under ICs or on inner layers, but here's some guesses on the card and notes on RAM cards in general, if anyone cares:

• Since it's using 512K x 8 chips, you'll have a pair of them on the 16-bit data bus for 1MB. Because of this you only select in 1MB boundaries, so for generating the RAM /CS lines you would only need to watch the last four address lines (A20-A23).
• The 74AC138 can take three address lines and decode them into eight RAM /CS lines, so it's a common choice for this.
• Theoretically if this were an 8MB card (it may have the capability as it seems to have unpopulated pads), it would select the 9th MB (1MB permanent RAM on the Portable + 8MB expansion = 9MB) when A20-A22 are low and A23 is high.
• Here's a table for matching up memory segments to address lines:

	A20​	A21​	A22​	A23​
1MB​	Low​	Low​	Low​	Low​
2MB​	High​	Low​	Low​	Low​
3MB​	Low​	High​	Low​	Low​
4MB​	High​	High​	Low​	Low​
5MB​	Low​	Low​	High​	Low​
6MB​	High​	Low​	High​	Low​
7MB​	Low​	High​	High​	Low​
8MB​	High​	High​	High​	Low​
9MB​	Low​	Low​	Low​	High​

• The 74AC138 data sheet provides a truth table:

• My guess would be that A20-A22 would be connected to A0-A2 on the 74AC138. In this case when A20-A22 are low (and the chip is enabled of course), Output 0 will be low. This however is in the Portable's permanent RAM space. Additionally, the bodge wire appears to connect Output 4 to where Output 7 would normally be connected, and Output 7 is not used. If the address lines are inverted (by a 74AC04 for example, or the PAL/GAL could do it too), then that would make sense as Output 7 would then be the Portable's permanent RAM space, which isn't connected to anything at this point. It seems likely that the bodge is just to correct a design flaw.
• A23 is likely connected to one of the active low enable lines on the 74AC138, so no RAM is selected when A23 is high. Then there may be additional logic for only when A20-A22 are low and A23 is high in order to select the 9th MB.
• There's lots of unpopulated spots for additional logic ICs on this board. My guess is that the additional logic is an alternative to that PAL/GAL.

 

[Sideburn]

Are you interested in taking a look at it and see if you can make it do something? If so I can ship it to you. My stock pile of bad boards is getting out of hand. I may just sell some unless someone else wants to have a look at them.

current list off the top of my head:

• this ram card
• two Mac portable logic boards (I’m going to re-cap and repair these).
• two non working Mac iicx boards. One has been re-capped and soft power circuit repaired but all it has is a clock. No activity on the bus. The other is untouched and has suffered bad corrosion from battery leakage. Probably beyond repair
• non working Radius Rocket. Don’t know where to begin with this one. It has a clock that’s about all I can see.
• non working SuperMac Video Spigot. Shows up on Nubus diags but crashes computer when supporting software is launched.

anyway if you are interested tinkering around with this ram card I’ll send it to you and anything else on that list that you might want to look at…

 

[SuperSVGA]

Sure, go ahead and mail it over if you'd like. I could probably draw up a basic schematic as well.

As for the Portable logic boards, I can look at them if you want but I imagine you could probably get them running pretty easily as well.
I think the only thing I have compatible with the Radius Rocket is a IIx, and I don't think I ever even got around to testing that after I recapped it, takes up too much desk space...
The Video Spigot could either be something simple or something really complex, if the issue isn't obvious it might take quite a bit of reverse engineering.

I just remembered I had seen one of these before in a 5MB variant, had to dig through my history a bit to find it. Though this also doesn't seem to be the original listing, the card might be getting passed around.

 

[Sideburn]

Cool yeah I’m going to do the portables next.

the rocket would be awesome to get running but it’ll be a challenge. It’s in good cosmetic condition. I probed it with the scope and all I see is oscillation from the crystal and the 68040. The 040 gets very warm.

I gave up on the iicx board that I re-capped if you wanted to check it out maybe. It now powers on and off and there’s clocks on all oscillators but it’s almost looking like the 030 is bad to me I dunno. I ended up recapping and repairing another one so I’m good to go with a working iicx.

the spigot is an odd one. It looks like it’s working from tattletech. Shows up on Nubus as “video spigot”. If the card is removed and I launch the ScreenPlay app it complains about no card. I put the card in and I get up to a spinning ball busy icon and then crash so it’s seeing the card. I’ve tried system 7.1 and 7.5 and QuickTime 1.0 and 1.6. And screenplay version 1.1.1 1.2 and 1.3. So that one will be a tough one as well. Probably a chip that’s on its last leg somewhere.

I need to get these portables done so that’s on the top of my list. And I may be buying another hybrid board off you. I need to check my inventory. I think I’ve bought about 3 of them already lol.