Meet my new Atom (warning: lots of images)

discussion of games, software, hardware & emulators relating to the Acorn Atom and Acorn System machines.
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VincentVega
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Meet my new Atom (warning: lots of images)

Post by VincentVega » Sat Sep 22, 2018 8:03 pm

If you follow the "today I received" thread elsewhere on the forum, you may know that I am now the owner of an Atom. I'm not too clued up on this particular Acorn computer, so I've started this thread in an attempt to gain some enlightenment from more knowledgable members of this sub-forum. I will highlight any questions in bold.

The first thing I do when receiving old computer hardware for my collection is to take it apart and give it a good clean. I decided to photograph this process for the Atom to (a) help me put it back together, (b) show anyone interested what's inside and (c) let the experts take a look to tell me what sort of specification it is.

So, here it is, balanced on the edge of the bath prior to being dismantled:

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It's in a pretty good state for something that's almost as old as I am. There are a few marks on it, plenty of dirt and dust and a strange white blob on the "0" key (more on that later). Nothing's been cut out of the rear or anywhere else.

Close-ups of the keyboard - fluff and dirt abound:

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Question: is it normal for there to be differing amounts of clearance above and below the keyboard? There's a gap of 2-3mm at the top, but no gap at all at the bottom.

Here's that strange "0" key:

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The key is a very good match for the others (texture, size, colour), though the typeface is different. Whilst we're on the subject of typefaces, I love the typeface on the Atom keys. Such a nice font!

The underneath is strangely featureless if, like me, you're more at home with Beebs:

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The screw had fallen out (again!) when I put the computer to one side before cleaning it. It came in handy when taking the photograph as my camera couldn't lock on to something to focus with all that beige. I may replace them with slightly longer ones so they are less prone to falling out.

Taking the lid off was strange. Unlike, well, all my other retro computers, the bottom half of the case has nothing in it - everything is attached to the top:

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The bubble-wrap had been added by the seller. Underneath that was the motherboard, with a surprising number of empty sockets:

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As you can see, it's an issue 4 board, and it has an add-on board of some sort that appears to take its power from the AC socket at the back. This is only secured to the board by the expansion connector, so tends to wobble about. I assume the smaller board at the top is for power or some such.

Undoing the four straight-headed screws nearest the corner of the board freed it from the top of the case and revealed even more fluff and grime:

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I think I'll be replacing the screws so they're all the same. Straight-headed screws in a computer seems wrong, somehow.

I put the case parts in the bath, ready for cleaning. The dirt really shows up compared to the white of the bath:

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Returning to the motherboard, I flipped it over to reveal the underside of the PCB and the speaker:

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This will be cleaned at some point with a toothbrush, distilled water and IPA.

Next, time to take all the key caps off. This was surprisingly easy - usually I have to resort to a flat-headed screwdriver, but these just popped off by hand (eventually). There was even more grime underneath:

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Once all the keys had been removed, they were popped in a container with warm water, and a load of anti-bacterial spray and Cif cleaner poured over:

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Back to the case halves - more Cif applied to both parts:

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Scrubbing then commenced:

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It was a pleasure to clean this case - there's not much inside, so it's easy to access all areas. The only fiddly bits were the corners and the grooves in the lid.

It came out looking rather lovely after a shower and another wipe with anti-bacterial spray:

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A magic eraser worked wonders getting rid of some of the stubborn marks.

Question: one thing I have noticed is the screw holes where the motherboard attaches to the case are not centred in the posts. Could this be why the keyboard is not aligned properly?

I then turned my attention to the keys and cleaned every one (always the most tedious part). I seem to have a couple of different styles:

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The key in the middle is "0". Clockwise from top, the others are CTRL, "9", "G" and "4". There are several like the "9" key on the right. Again, the "0" key with its weird typeface is a really good match for the others.

Anyway, all the keys were cleaned, dried and blow-dried (to get rid of any lingering water) and laid out:

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(The "5" key is strangely missing from the picture, no idea why.)

Notice anything different? Yes, the white blob has vanished from the "0" key, all on its own!

Finally, the case parts and all the keys were put in the airing cupboard for a few days to dry out.

To the motherboard - it's time to think about PSUs. The machine came with the original 8V Acorn PSU. I'd like to use it with something modern, so I took the metal bracket off the back to see if links 6 and 7 had been made.

The answer is "no" (and there aren't even pin headers):

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So I'll be soldering some of those on as my first modification, and sourcing a decent PSU from somewhere. RS have some 5V Meanweall ones with plenty of oomph, so I'll probably treat the Atom to one of those (e.g. this one) and change the power socket.

I decided to take the expansion board off to see what's underneath and to aid cleaning when I get around to it. I couldn't be bothered getting my soldering stuff out, so I just cut the wire in half (ugh). There are even more empty sockets:

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Question: is it normal for there to be this many empty sockets on an Atom? Can anyone summarise what they all do?
Question: is this a good enough view of the board to be able to identify what memory/video capacity the computer has?

As I mentioned on the recent arrivals thread, the computer also came with a "spare" LS138 chip, a pin header, a resistor and a capacitor in a small plastic bag. Question: do these have any specific purpose? Were they removed when the expansion board was added?

A close up of the expansion board, above and below:

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And that's it for today's instalment. Tomorrow, I hope to be giving the motherboard a clean, and I'll be posting a few more questions, mainly about add-ons.

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danielj
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Re: Meet my new Atom (warning: lots of images)

Post by danielj » Sat Sep 22, 2018 9:15 pm

All the images are broken :?

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Multiwizard
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Re: Meet my new Atom (warning: lots of images)

Post by Multiwizard » Sat Sep 22, 2018 9:21 pm

Hi,

thanks for all the pics... :D

Ok the white dot is gone, so the original Issue 4 "0" key-cap must been replaced with an Acorn System keyboard key-cap which has a smaller zero printed on... :D

https://commons.wikimedia.org/wiki/File ... _board.jpg


Greetings, Wim... :-)

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jms2
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Re: Meet my new Atom (warning: lots of images)

Post by jms2 » Sat Sep 22, 2018 9:25 pm

Images look OK to me.

I'm not exactly an expert, but I would say yes, it is normal to have this many empty sockets if you have an expansion board of this kind. All the RAM is moved into the separate board, leaving all the old 2114 DRAM sockets free on the motherboard. My Atom looks like this. (Well actually it looks like a right mess, but that's because it has some nasty white sockets and lots of spaghetti like add-on wiring!)

Looking more closely at your add on board, it seems to contain 4116 DRAMs (64k in total I think?). Mine has static ram, and ROMs, so is a different design.
Last edited by jms2 on Sat Sep 22, 2018 9:28 pm, edited 2 times in total.

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Re: Meet my new Atom (warning: lots of images)

Post by 1024MAK » Sat Sep 22, 2018 10:34 pm

jms2 wrote:
Sat Sep 22, 2018 9:25 pm
Looking more closely at your add on board, it seems to contain 4116 DRAMs (64k in total I think?). Mine has static ram, and ROMs, so is a different design.
4116 DRAM are 16k x 1 bit type. So eight of them gives 16k bytes.
4116 DRAM require +12V and -5V supplies in addition the the normal +5V supply.
4116 DRAM pin-out_p.png
4116 DRAM pin-out
4116 DRAM pin-out_p.png (39.9 KiB) Viewed 451 times
When you first power this up, it's important to confirm that the -5V supply is present. A missing -5V supply can result in the 4116 DRAM chips self destructing :( If missing, switch off at once.
It's also wise to test the +12V.

Both the -5V and +12V have a tolerance of +/-10%

Pin 1 is VBB, which is -5V (-5.5V to -4.5V)
Pin 8 is VDD, which is +12V (+10.8V to +13.2V) (although lower than 11.3V normally indicates a problem).
Pin 9 is VCC, which is +5V (+4.75V to +5.25V)
Pin 14 is VSS, which is 0V (ground/GND) (no need test this if using another 0V/GND connection)

In view of the above power requirements, the extra power supply board is almost certainly provided for this reason. And I suspect it may want 8V DC input.

Mark

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hoglet
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Re: Meet my new Atom (warning: lots of images)

Post by hoglet » Sun Sep 23, 2018 6:31 am

Here is a link to the manual for your DRAM expansion board:
viewtopic.php?f=44&t=13338

The DRAM expansion board looks like it is configured to map the 16K RAM at addresses #2800-#67FF.

This leaves IC 52/53 providing #0000-#03FF and IC 41/42 providing #8000-#83FF

It's power supply needs to be fed with between +7.5V and 11V, so that's going to make conversion of the Atom to run off a single 5V power supply more challenging.

The 74LS138 was removed from IC6 when the DRAM board was fitted. It's only needed if 2114L RAM chips are fitted in IC10-IC19, as it provides their chip select signals.

Dave
Last edited by hoglet on Sun Sep 23, 2018 6:38 am, edited 2 times in total.

VincentVega
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Re: Meet my new Atom (warning: lots of images)

Post by VincentVega » Sun Sep 23, 2018 1:19 pm

Thanks for all the responses, everyone. I cleaned the motherboard today, so that's one more task done.

Right, let's talk add-ons. I want to keep the outside of the machine looking as original as possible, but I'd like to change the insides to make this computer more capable. So I've had a look at the retro hardware list on Elminster's Github (https://elminster.github.io/hardware) and it lists some Atom things that look quite interesting:

1. Prime's Atom 32K RAM/ROM board.
2. Prime's Atom Colour Board.
3. Sir Morris's AtoMMC2 SC Card.

Are any of these still available for purchase? I'd be particularly interested in the RAM board and the MMC.

I've been reading through the manual, in particular the pages detailing the memory map. I would like to be able to ditch the ancient Acorn PSU, even if it means ditching the RAM board as well. If I could replace the latter with a modern solution, that would be ideal.

It also looks like my Atom is equipped with the bare minimum of video memory, namely #8000 to #83FF, as Dave mentions. Is it still possible to obtain 2114L chips? I assume I'd have to resort to eBay, or similar.

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Re: Meet my new Atom (warning: lots of images)

Post by tricky » Sun Sep 23, 2018 1:41 pm

I have recently bought 1. Prime's Atom 32K RAM/ROM board. and 3. Sir Morris's AtoMMC2 SC Card. although I have only had time to play a little with 3.
They both seem like great bits of kit. I don't think 2. Prime's Atom Colour Board. is still available.
There is a mod to make the Atom take a regulated 5v input only, which seems simple and makes the Atom more reliable although I have no details.
The MMC board also comes with a connector for a joystick, although again, I haven't tried this yet.
There is more info in my Atom thread including my unusual power connector mounting position.

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hoglet
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Re: Meet my new Atom (warning: lots of images)

Post by hoglet » Sun Sep 23, 2018 1:50 pm

VincentVega wrote:
Sun Sep 23, 2018 1:19 pm
It also looks like my Atom is equipped with the bare minimum of video memory, namely #8000 to #83FF, as Dave mentions. Is it still possible to obtain 2114L chips? I assume I'd have to resort to eBay, or similar.
It's not easy to find 2114L RAM chips, so expect to pay for them. You'll also have Atom screen noise to put up with.

Phill's Colour board replaces the 2114L RAM chips, but is now discontinued for technical reasons:
viewtopic.php?f=3&t=12801&p=164586

He may still have some bare PCBs, and it is possible to use it as a noise killer / RAM board without using it's video output.

Another option is to do your own replacement with a 6264 8K Static RAM:
http://acornatom.nl/hardware/cmos/cmos.html

See the Atom in this post for one fitted.

Maybe there is scope for a new minimal video RAM board that just comprises the noise-killer and an 8K RAM chip.

Dave
Last edited by hoglet on Sun Sep 23, 2018 1:51 pm, edited 1 time in total.

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Re: Meet my new Atom (warning: lots of images)

Post by oss003 » Sun Sep 23, 2018 4:28 pm

Here is a link to some Atom expansions with a link to the developer:

viewtopic.php?f=13&t=8168&p=86259&hilit ... ard#p86259

Question: is it normal for there to be differing amounts of clearance above and below the keyboard? There's a gap of 2-3mm at the top, but no gap at all at the bottom.
Question: one thing I have noticed is the screw holes where the motherboard attaches to the case are not centred in the posts. Could this be why the keyboard is not aligned properly?

Answer: I haven't noticed this before but you're right. Looks like this is normal, looking at other pictures on the internet.

Question: do these have any specific purpose? Were they removed when the expansion board was added?
Answer: I noticed that C11 is not installed (Break delay 10 uF)

Also the datalines are hardwired to PL6/7 by using wires in IC4.

Greetings
Kees
Last edited by oss003 on Sun Sep 23, 2018 4:29 pm, edited 1 time in total.

VincentVega
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Re: Meet my new Atom (warning: lots of images)

Post by VincentVega » Sun Sep 23, 2018 5:15 pm

oss003 wrote:
Sun Sep 23, 2018 4:28 pm
Here is a link to some Atom expansions with a link to the developer:

viewtopic.php?f=13&t=8168&p=86259&hilit ... ard#p86259
Thanks for that - most helpful. I've sent both of the developers a PM, so hopefully they'll have something available!
I noticed that C11 is not installed (Break delay 10 uF)
Hmm, I wonder if that's what the random capacitor is with the LS138 chip? I'll have a look in a bit.
hoglet wrote:
Sun Sep 23, 2018 1:50 pm
It's not easy to find 2114L RAM chips, so expect to pay for them. You'll also have Atom screen noise to put up with.
Yes, I noticed that the prices are quite steep on eBay. I was hoping that I wouldn't have to resort to eBay, as you never know what's fake and what isn't!
Phill's Colour board replaces the 2114L RAM chips, but is now discontinued for technical reasons:
I missed that thread, what a shame!
Maybe there is scope for a new minimal video RAM board that just comprises the noise-killer and an 8K RAM chip.
Sounds like a great idea!
Last edited by VincentVega on Sun Sep 23, 2018 5:16 pm, edited 1 time in total.

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Re: Meet my new Atom (warning: lots of images)

Post by VincentVega » Sun Sep 23, 2018 6:00 pm

How tolerant is the Atom of differing specifications of 2114 chips? The ones in ICs 42 and 43 are MM2114N-L, which according to this page are 450ns parts.

I can get some slightly different specifications ones - MM2114N-3 (300ns) - at £2.99 each from here. Would these work?

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Re: Meet my new Atom (warning: lots of images)

Post by hoglet » Sun Sep 23, 2018 6:12 pm

VincentVega wrote:
Sun Sep 23, 2018 6:00 pm
I can get some slightly different specifications ones - MM2114N-3 (300ns) - at £2.99 each from here. Would these work?
Faster is fine, but those are not the low power variety that is usually fitted.

Each one can draw up to 100mA according to the datasheet.

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Re: Meet my new Atom (warning: lots of images)

Post by oss003 » Sun Sep 23, 2018 6:21 pm


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Re: Meet my new Atom (warning: lots of images)

Post by Prime » Sun Sep 23, 2018 6:25 pm

hoglet wrote:
Sun Sep 23, 2018 1:50 pm
Maybe there is scope for a new minimal video RAM board that just comprises the noise-killer and an 8K RAM chip.
The Mk3 colour board could do this, if you leave off the LMH1251 and the rest of the colour circuitry. I've a slightly modified version of that board where I added the VCC filter from the Atom circuit to the power circuit for the buffer transistors, to see if it would improve things. Though the colours are not quite correct on this board it's easier to produce and setup. So I may get a small run of the Mk 3.7 (last produced was 3.6) made to test this. If I have spares I'll of course let people have them....even if just as a RAM and noise killer!

In that role they could also be supplied as a bare board as the only surface mount chip is the LMH1251, I seem to remember in the original run I supplied them to a couple of people with just this mounted as they where OK soldering PTH but not surface mount stuff....

Cheers.

Phill.

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Re: Meet my new Atom (warning: lots of images)

Post by VincentVega » Sun Sep 23, 2018 6:54 pm

hoglet wrote:
Sun Sep 23, 2018 6:12 pm
VincentVega wrote:
Sun Sep 23, 2018 6:00 pm
I can get some slightly different specifications ones - MM2114N-3 (300ns) - at £2.99 each from here. Would these work?
Faster is fine, but those are not the low power variety that is usually fitted.

Each one can draw up to 100mA according to the datasheet.
Ah, I'd missed the "L".

This place seems to have plenty of different 2114s, all at £3 each. Here is a National Semiconductor, MM2114-15L (150ns) part, and they have 598 in stock. It looks a good match from the datasheet.

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Re: Meet my new Atom (warning: lots of images)

Post by roland » Sun Sep 23, 2018 9:23 pm

I'd still advice a static 8k cmos board for video memory because it's cheaper, draws much less power ( and so produces less heat) and gives an additional 2k of workspace that will be used by many programs.
256K + 6502 Inside
MAN WOMAN :shock:

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