Acorn Atom newly acquired not resetting

discussion of games, software, hardware & emulators relating to the Acorn Atom
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John Ferguson
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Acorn Atom newly acquired not resetting

Post by John Ferguson » Thu Mar 22, 2018 2:52 pm

I have just purchased an Atom with a colour board with a view to restoring it.

Have bypassed the regulators and obtained a new 5volt 2.5amp DC power supply. This came with 2.1mm DC plug.

This fits the existing Atom DC socket by enlarging the opening with a soldering iron and fitting 2.5mm adapter to the 2.1 plug to the power supply.

I have the random display on powering up but the break key does not bring up the Atom prompt.

I would very much like some advice on the next step to get the machine working.

John
Last edited by John Ferguson on Fri Mar 23, 2018 8:04 am, edited 1 time in total.

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DutchAcorn
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Re: Acorn Atom newly acquired not resetting

Post by DutchAcorn » Thu Mar 22, 2018 8:14 pm

John Ferguson wrote:I have just purchased an Atom with a colour board with a view to restoring it.

Have bypassed the regulators and obtained a new 5volt 2.5amp DC power supply. This came with 2.1mm DC plug.

This fits the existing Atom DC socket by enlarging the opening with a soldering iron.

I have the random display on powering up but the break key does not bring up the Atom prompt.

I would very much like some advice on the next step to get the machine working.

John
Can you post a picture of the board?
John Ferguson wrote:This fits the existing Atom DC socket by enlarging the opening with a soldering iron.
:shock:
Paul

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oss003
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Re: Acorn Atom newly acquired not resetting

Post by oss003 » Thu Mar 22, 2018 8:22 pm

Hi John,

it's hard to tell if it's a problem with the colourboard or something else.
The best way is to try to get the Atom working without colourboard and if it's working ok, then try to install the colourboard.

Here's a kind of troubleshooting guide: viewtopic.php?f=44&t=6318&p=60505&hilit ... ion#p60505

Greetings
Kees

Graeme Roberts
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Re: Acorn Atom newly acquired not resetting

Post by Graeme Roberts » Thu Mar 22, 2018 9:00 pm

Hello John,
I have the random display on powering up but the break key does not bring up the Atom prompt.
Are you sure the break key is actually working? Try flipping the machine over and shorting the two keyboard contacts for the break key with a screwdriver or similar which will force it to be registered. If the machine resets, you'll know the mechanism for the key is defective.

Otherwise I'd take Kees' advice and strip all non-essential boards off the machine and run it in its basic configuration. Hope this helps.

Graeme.

John Ferguson
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Re: Acorn Atom newly acquired not resetting

Post by John Ferguson » Fri Mar 23, 2018 8:10 am

Hi Paul, Kees, and Graeme

I will try all you have said. Many thanks for the responses.

I will post a photo of the board later today.

John

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Re: Acorn Atom newly acquired not resetting

Post by John Ferguson » Fri Mar 23, 2018 4:23 pm

This is my Atom with the colour and rom boards

John
Atom with colour board revised.jpg

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DutchAcorn
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Re: Acorn Atom newly acquired not resetting

Post by DutchAcorn » Sat Mar 24, 2018 11:10 am

Looks like a typical Atom: nicely modded :D

Lots of potential for loose connections and bad joints.

First thing to try is to make sure that everything is seated well into their sockets, especially the rom extension and the colour board.

If that doesn't help then go for the Kees' suggestion to bring the board into a basic configuration (after checking the break key is functional).
Paul

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Re: Acorn Atom newly acquired not resetting

Post by John Ferguson » Sat Mar 24, 2018 4:00 pm

This afternoon the Atom started to work amazingly so my guess is that various chips need to be pressed home. Loose fitting devices as suggested must have been the problem. No doubt I accidentally disturbed them. Break key as normal.

The Atom has a switch to select colour or black and white. Changing over the colour modes they become instantly available. A very nice modification by the previous owner.

Now need to figure out the link addresses for the Rom chips.

Can people suggest how I could do this?

Will run the memory checking programmes.

John

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Re: Acorn Atom newly acquired not resetting

Post by Prime » Sat Mar 24, 2018 6:50 pm

John Ferguson wrote: Now need to figure out the link addresses for the Rom chips.
I would suggest that the roms are at #A000, though there may also be a paging register involved, as there are multiple sockets, an address decoder and a latch on the rom board, in this way multiple roms can be paged in by writing a value to the latch, I think typically the address #BFF0 was used, though this would depend on the decoding for the latch.

Cheers.

Phill.

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Re: Acorn Atom newly acquired not resetting

Post by bprosman » Sat Mar 24, 2018 7:20 pm

Lots of potential for loose connections and bad joints.
Indeed I see a lot of single sided IC sockets.

John Ferguson
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Re: Acorn Atom newly acquired not resetting

Post by John Ferguson » Sun Mar 25, 2018 6:44 pm

What is interesting now the Atom is working is that the Atom prompt appears instantly when powering up the computer. The random display no longer appears and the break key is not needed.

The capacitor c11 was not installed for the break key circuit.

I am wondering also whether link 5 shown on the circuit diagram near the 6847 video chip is involved. This has a connection to the css pin on the 6847 device.

John

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roland
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Re: Acorn Atom newly acquired not resetting

Post by roland » Sun Mar 25, 2018 7:50 pm

In a normal situation the CSS pin of the 6847 is connected to PC3 of the 8255 and it is used to select one of the colour sets of the 6847. You can check this by typing ?#B002=8 The colour of the text on the screen should change from green to orange (or something like that). If the colour does not change then PC3 is tied to 0v.
256K + 6502 Inside
MAN WOMAN :shock:

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oss003
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Re: Acorn Atom newly acquired not resetting

Post by oss003 » Sun Mar 25, 2018 8:17 pm

The normally used addresses for romswitching are: #A000, #BFFF.
You can test this by printing the sum of all bytes:

Code: Select all

10 S=#A000  (or #BFFF)
20 ?S=0;GOS.a;P.&T'
30 ?S=1;GOS.a;P.&T'
40 END
50aT=0
60 F.A=0TO#FFF S.4
70 T=T+#A000!A
80 N.
90 RETURN
If the printed sums are different, then you have the right switchaddress.

The colourboard is also an interesting one, is it only connected to PL4?

Greetings
Kees

John Ferguson
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Re: Acorn Atom newly acquired not resetting

Post by John Ferguson » Mon Mar 26, 2018 11:50 am

Hi Kees

Thank you for the programme to help gain access to the roms.

The colour board is connected to PL4 and the output is connected to the negative end of the C2 capacitor via a switch. C2 is no longer directly connected to the negative pad on the Atom board.

The switch when operated joins the original negative connection pad of C2 to the negative end of C2 to give a black and white screen as supplied.

When the switch is operated in the other direction you get the colour screen as the output from the colour board is then connected to C2.

Problem I have at the moment is that the Atom keeps locking up and will not reset. It may be the colour board is not being held in a stable condition.

As advised I am removing all the add on boards to see if the Atom will run as supplied.

John

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oss003
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Re: Acorn Atom newly acquired not resetting

Post by oss003 » Mon Mar 26, 2018 12:43 pm

Hi John,

When the colourboard is only connected to PL4 and a few wires, it's not citical for the Atom and the Atom will not hang on this.
The best way is to remove every chip, clean it's legs and socket and then reseat it.
This is more critical.

Greetings
Kees

John Ferguson
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Re: Acorn Atom newly acquired not resetting

Post by John Ferguson » Mon Mar 26, 2018 12:55 pm

Hi Kees

What is odd about the locking up is that the Atom behaves normally upside down but not in the normal position. I have tried pressing every chip into their socket.

I take your point about cleaning the legs but I wonder whether you know which chips to look at.

Also while I can clean the legs how would you clean a socket?

John

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oss003
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Re: Acorn Atom newly acquired not resetting

Post by oss003 » Mon Mar 26, 2018 1:04 pm

Insert and remove a chip several times into the socket or use contact spray.
If you want to have good contact of the chips, remove the sockets and replace them with the turned pin ones but this is a PITA job.

It can also be a bad solder point, not soldered through on both sides of the PCB or broken from the PCB.

Greetings
Kees

John Ferguson
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Re: Acorn Atom newly acquired not resetting

Post by John Ferguson » Mon Mar 26, 2018 3:44 pm

Hi Kees

I have just sprayed the Atom with WD40 and so far the Atom does not lock up.

It may have cured the problem. It was your idea to use contact cleaner that helped me

Now for memory testing. I can see faults in the graphic modes.

John

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Re: Acorn Atom newly acquired not resetting

Post by IanS » Mon Mar 26, 2018 8:04 pm

John Ferguson wrote:I have just sprayed the Atom with WD40 and so far the Atom does not lock up.
:shock:
WD40 is almost never the right answer, to any question. Spraying it on a circuit board is bizzare.
"The long-term active ingredient is a non-volatile viscous oil which remains on the surface to which it is applied, giving lubrication and protection from moisture"

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Re: Acorn Atom newly acquired not resetting

Post by John Ferguson » Tue Mar 27, 2018 1:39 pm

Thanks for the comments about the use of WD40.

This Atom had been stored in very damp conditions and corrosion had started to some degree.

WD40 seemed suitable to me for the following reasons as stated on the can.

It drives out moisture, cleans and protects, loosens rusted parts, and frees sticky mechanisms.

I sprayed it into the sockets for the processor, and the 2 chips that control the keyboard and generally over the solder side of the Atom PCB.

The result is that an Atom which only worked upside down is in working order. The visible fault in the graphics memory is now no longer present.

It seems to have done the job so I am not particularly worried about the residue of oil.

Further tests of memory are intended as well as the cassette system.

John

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