Acorn Atom not working

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John Ferguson
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Acorn Atom not working

Postby John Ferguson » Sun Oct 08, 2017 10:33 am

After nearly 40 years I have returned to my first love which was the Acorn Atom which I built in 1980 from a kit and added the colour board.

I have always regretted leaving it behind when an Atari and other home computers and PC came available. I tried various emulators but they did not capture my attention and restore my experience in the same way.

So in recent years and getting older I started to look around on the internet and on Ebay to see if I could buy one and get it working with only a limited amount of electrical knowledge. I know how to use a digital multi-meter but have no knowledge about the use of scopes. I have the technical manual, user guide and the circuit diagram.

Then I bought one on Ebay but this did not have a power supply. All the keys appear to work but on powering up no signal is received on a TV or monitor. Pressing break does nothing.

I bypassed the existing regulators by putting in the links 6 and 7 and fitted a new socket on the PCB. Then I connected a 5v DC SMP power supply.

Having just discovered this forum I am wondering whether a member could give me some advice on what to do next. It would be much appreciated.

John

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DutchAcorn
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Re: Acorn Atom not working

Postby DutchAcorn » Sun Oct 08, 2017 10:39 am

Welcome to Stardot, John! You have come to the right place for help :D

How far have you got in powering it up and connecting it to a TV/monitor?

If you type a few random character and then press return, does it beep?

*edit: now see that you do not get any output on a TV

Do you realise that the port on the Atom is UHF out and you need to tune into the right frequency on the TV? Newer TV's may have trouble finding the signal.
Paul

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hoglet
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Re: Acorn Atom not working

Postby hoglet » Sun Oct 08, 2017 10:48 am

Why not start by posting a couple of high resolution photos of the insides?

Here's a link to the schematic (the best quality scan I'm aware of):
https://acorn.huininga.nl/pub/docs/circ ... iagram.gif

As Paul said, if you are connecting a TV via the UHF modulator, then make sure your TV has an analog tuner. What model is the TV?

A good first step is to make sure you can measure 5V across the GND and VCC pins of the 6847.

You can also get a composite video signal out of the Atom on PL4 pins 9 and 10. Pin 9 is the video and Pin 10 is GND. This should work with the composite video input of most modern TVs.

(It's actually quite rare for an Atom to produce no composite video output, as really all that has to be working is the 6847 and a couple of transistors)

Dave

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hoglet
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Re: Acorn Atom not working

Postby hoglet » Sun Oct 08, 2017 10:57 am

Oh, and Welcome! (above post edited a bit)

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danielj
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Re: Acorn Atom not working

Postby danielj » Sun Oct 08, 2017 11:24 am

Welcome John :) the good news is almost every atom can be fixed!

d.

John Ferguson
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Re: Acorn Atom not working

Postby John Ferguson » Sun Oct 08, 2017 11:35 am

Thank you very much for the comments received.

Its really good belonging to this forum.

There is no bleep after typing say line 10 test and pressing return. Break already pressed before.

Monitor connection to pins 9 and 10 of PL4 already made.

TV is a modern Samsung one. In addition to the monitor connection via component on the TV I connected the TV aerial to the modulator and set the channel on the TV to 36.

I will check some voltages on the 6847 and the 6502.

I imagine that as there is no bleep something major is not happening hence no output.

I will post some images.

John

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CMcDougall
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Re: Acorn Atom not working

Postby CMcDougall » Sun Oct 08, 2017 11:44 am

welcome John :)

typing 10 junk, would be ok until RUN
try CNTL G ,this should Beep.

have fun getting it going!
ImageImageImage

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hoglet
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Re: Acorn Atom not working

Postby hoglet » Sun Oct 08, 2017 11:49 am

Even if the 6502 processor is removed (i.e. no code at all running) you should still get some video output like this:
250da296f9ed7e3e3538bfb548248d6ebd7d9322.JPG

What you see here is the 2114 Video RAM chips initialized to random values on power up.

I would start by checking there is power to the appropriate pins of the 6847.

Also, do post some photos!

Dave

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Multiwizard
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Re: Acorn Atom not working

Postby Multiwizard » Sun Oct 08, 2017 2:15 pm

Hi John,

welcome to this great Forum... :D


Greetings from my little Dutch Acorn Attic, Wim... :-)

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martinw
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Re: Acorn Atom not working

Postby martinw » Sun Oct 08, 2017 2:58 pm

Welcome John :)

Might be worth a read ...

viewtopic.php?f=44&t=13531

... I was in a similar position not so long ago.

Martin

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oss003
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Re: Acorn Atom not working

Postby oss003 » Sun Oct 08, 2017 3:00 pm

Hello John,

welcome and enjoy the forum .....

Maybe this post can help you: viewtopic.php?f=44&t=6318&p=60505&hilit=minimal+configuration#p60505

Greetings
Kees

John Ferguson
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Re: Acorn Atom not working

Postby John Ferguson » Sun Oct 08, 2017 3:23 pm

Well after the advice about checking the voltages sure enough when I fitted a new PCB connector for the power supply I had failed to connect one of the 2 0v connections.

The Atom is now working satisfactorily using component video only. Nothing via the modulator but I do not need it.

Only thing outstanding is that the loudspeaker is hardly audible.

Can you tell me how to fix this? Do I need a new speaker.

Next is the cassette recorder for saving programmes again from Ebay.

I assume that the connections for the microphone and earphones provided on the cassette recorder plus a ground connection common to both will do the job. Is this okay?

The encouragement I have received really helped.

John

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martinw
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Re: Acorn Atom not working

Postby martinw » Sun Oct 08, 2017 3:43 pm


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hoglet
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Re: Acorn Atom not working

Postby hoglet » Sun Oct 08, 2017 4:12 pm

John Ferguson wrote:Can you tell me how to fix this? Do I need a new speaker.

It's possible that capacitor C5 needs replacing.

If you look at the speaker circuit on the schematic (linked in my post earlier) it's quite simple.

Dave

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Re: Acorn Atom not working

Postby John Ferguson » Sun Oct 08, 2017 7:38 pm

Thanks Dave for your comment about the speaker.

Does anyone know where I can get a list of commands for the floating point Rom?

John

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hoglet
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Re: Acorn Atom not working

Postby hoglet » Sun Oct 08, 2017 7:42 pm

John Ferguson wrote:Does anyone know where I can get a list of commands for the floating point Rom?

Atomic Theory and Practice, Chapter 22 (Extending the Atom):
viewtopic.php?p=62322#p62322

Code: Select all

Floating-Point Statements
COLOUR, FDIM, FIF, FINPUT, FPRINT, FPUT, FUNTIL, STR

Floating-Point Functions
ABS, ACS, ASN, ATN, COS, DEG, EXP, FGET, FLT, HTN, LOG, PI, RAD, SGN, SIN, SQR, TAN, VAL

Floating-Point Operators
!, %, ^


Dave

John Ferguson
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Re: Acorn Atom not working

Postby John Ferguson » Mon Oct 09, 2017 9:31 am

Outstanding issues for me now that the Atom is working are:-

How can I print from the Atom?

I see that there is an add on AtoMMC for solid state storage. How can I obtain this please?

John

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oss003
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Re: Acorn Atom not working

Postby oss003 » Mon Oct 09, 2017 10:23 am

To start printing type P.$2 and to stop printing type P.$3 but IC's 1 and 50 must be installed.

You can find a lot of Atomic expansions here: http://www.stardot.org.uk/forums/viewto ... cts#p86259

Greetings
Kees
Last edited by oss003 on Mon Oct 09, 2017 10:30 am, edited 1 time in total.

John Ferguson
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Re: Acorn Atom not working

Postby John Ferguson » Mon Oct 09, 2017 10:28 am

I thought I would show an image of my Atom's circuit board.

Image

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oss003
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Re: Acorn Atom not working

Postby oss003 » Mon Oct 09, 2017 10:31 am

Hi John,

You need IC's 1 and 50 to print.

Greetings
Kees

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DutchAcorn
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Re: Acorn Atom not working

Postby DutchAcorn » Mon Oct 09, 2017 11:14 am

oss003 wrote:Hi John,

You need IC's 1 and 50 to print.

Greetings
Kees

And you would need a connector fitted on PL5 to plug the parallel printer cable into the Atom.
Paul

John Ferguson
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Re: Acorn Atom not working

Postby John Ferguson » Mon Oct 09, 2017 12:30 pm

Thank you for the advice about printing.

John

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Multiwizard
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Re: Acorn Atom not working

Postby Multiwizard » Mon Oct 09, 2017 5:55 pm

Hi,

don't we also need a little wire from pin1 of PL4 to pin17 of the PL5 for the 8th bit? :-k

Or something like this? :?


Greetings, Wim... :-)

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oss003
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Re: Acorn Atom not working

Postby oss003 » Mon Oct 09, 2017 7:41 pm

That's only of you want to send 8 bits to the printer instead of 7.

Greetings
Kees

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Re: Acorn Atom not working

Postby John Ferguson » Mon Oct 09, 2017 8:21 pm

I believe the Atom printer routines only output 7 bits. Is this a problem?

John

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oss003
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Re: Acorn Atom not working

Postby oss003 » Mon Oct 09, 2017 8:24 pm

It will work for ASCII but you have to write a special 7 bit graphic print routine to make a screendump.
This is much easier with 8 bits.

Greetings
Kees

John Ferguson
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Re: Acorn Atom not working

Postby John Ferguson » Mon Oct 09, 2017 8:48 pm

Thank you Kees.

I remember that when I owned the atom way back I did write such a routine.

Perhaps I will make it one of my projects.

John

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Multiwizard
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Re: Acorn Atom not working

Postby Multiwizard » Mon Oct 09, 2017 9:13 pm

oss003 wrote:This is much easier with 8 bits.

Ahaaa... LOL :mrgreen:


Greetings, Wim... :-)

John Ferguson
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Re: Acorn Atom not working

Postby John Ferguson » Wed Oct 11, 2017 7:13 am

I am wondering whether it is possible to get some games for my Atom.

Could someone comment please.

John

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Multiwizard
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Re: Acorn Atom not working

Postby Multiwizard » Wed Oct 11, 2017 7:16 am

John Ferguson wrote:I am wondering whether it is possible to get some games for my Atom.

Could someone comment please.

John

On cassette, floppy or SD files?


Greetings, Wim... :-)


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