Acorn Atom power connections on motherboard.

discussion of games, software, hardware & emulators relating to the Acorn Atom and Acorn System machines.
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1024MAK
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Re: Acorn Atom power connections on motherboard.

Post by 1024MAK » Thu May 23, 2019 4:10 pm

Schematic of the Acorn Atom 5V power circuits:
Image

Mark
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Acorn Atom 5V power circuits

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Re: Acorn Atom power connections on motherboard.

Post by apt-e » Thu May 23, 2019 8:16 pm

Ah right, that explains it, thank you Mark. Very useful.

I will have to start looking at the chips in this case, chip puller, now where are you...…….
Last edited by apt-e on Fri May 24, 2019 12:54 pm, edited 1 time in total.

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Re: Acorn Atom power connections on motherboard.

Post by 1024MAK » Thu May 23, 2019 9:50 pm

Chip puller :shock: [-X

I prefer to carefully use a suitable flat bladed screwdriver. Some use a blunt knife. Others use a L shape tool. The idea being to leaver the chip out slowly, working at one end, then the other, then at the other end, repeatedly until the chip gently and slowly is released from the socket. Don’t leaver against the PCB or you risk track damage. Leaver against the plastic of the socket.

The simple tong type chip pullers have a nasty habit of bending pins at one end of the chip, as one end releases suddenly, the chip then rotates as it comes out, bending pins in the process :(

Mark

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Re: Acorn Atom power connections on motherboard.

Post by apt-e » Fri May 24, 2019 7:14 am

Hi Mark,
Thanks for the advice, I tend to use a blunt small screw drive. I purchased a set of chip pullers a while ago, but after your advice, I wont use them.

Thanks

Paul

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Re: Acorn Atom power connections on motherboard.

Post by IanB » Fri May 24, 2019 2:06 pm

roland wrote:
Wed May 15, 2019 7:26 pm
If you're interested I have an original power connector for the Atom.
My Atom came without a power connector and there doesn't seem to be a modern pin compatible replacement available but I discovered that the power connectors used in the original Acorn Econet clocks and terminators were identical:

http://chrisacorns.computinghistory.org ... Clock.html
http://chrisacorns.computinghistory.org ... 1Term.html

This info probably isn't that useful as those things are rarer than the Atoms but as it happened I already had one which I had built inside an Econet bridge with a hard wired power connection so the socked wasn't being used. (In any case it is easier to bodge in a replacement socket on a clock/terminator than an Atom)

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Re: Acorn Atom power connections on motherboard.

Post by apt-e » Mon May 27, 2019 11:06 am

Hi All,
I removed the video ram chips and replace ic42/43 with various chips, all with the same result.
Atom will post with broken screen with white lines....
20190527_115046.jpg
Press break and screen settles for a while and looks ok, you can type ok.
20190527_115127.jpg
Screen loses sync from time to time. but no odd characters appear.

Type clear 4 and you get ….
20190527_115143.jpg
Type clear 0 and get get …..
20190527_115009.jpg
When the screen goes off, you can still make the Atom beep, so it is still working, seems to be a video fault.

Can I connect the Atom via the pin outs to composite any other format.

Could bad caps be causing this, some do indeed have a bit of brown crud on the ends.

Thanks all.

Paul

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Re: Acorn Atom power connections on motherboard.

Post by -B- » Mon May 27, 2019 11:48 am

Garbage on screen at startup is normal. You can increase the value of the reset capacitor C11 to stop it.

How are you connecting the video? RF?
There is a composite video output on pin 9 of PL4 and pin 10 is GND.

Neil.
Atom | BBC Model A | BBC Model B | Electron | Olivetti PC128S.

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Re: Acorn Atom power connections on motherboard.

Post by roland » Mon May 27, 2019 12:10 pm

Yes, bad caps can cause such blurry characters. Especially C4 (22µF) is famous for this.

O, and it looks like you have only 1KB of video ram installed when you entered CLEAR 4.
Last edited by roland on Mon May 27, 2019 12:11 pm, edited 1 time in total.
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Re: Acorn Atom power connections on motherboard.

Post by apt-e » Mon May 27, 2019 12:19 pm

Hi,
Yes, the clear 4 command was issued with only 2 chips in IC42 and 43, the rest removed, is this what is supposed to look like.

I am currently using the RF which I know isn't the best, but I will make up a cable to use the pins instead.

I will replace C4 when I get the chance, and hopefully this will solve the sync problem.

Thanks all

Paul

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Re: Acorn Atom power connections on motherboard.

Post by roland » Mon May 27, 2019 12:54 pm

apt-e wrote:
Mon May 27, 2019 12:19 pm
Yes, the clear 4 command was issued with only 2 chips in IC42 and 43, the rest removed, is this what is supposed to look like.
Yes, with only two chips in video memory this is normal and it is supposed to look like this. When all 2114's are installed then CLEAR 4 should give a larger black rectangle.
apt-e wrote:
Mon May 27, 2019 12:19 pm
I will replace C4 when I get the chance, and hopefully this will solve the sync problem.
It might solve that as well. Beware that the Atom vsync is 60Hz and some televisions and monitors might not like that.
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Re: Acorn Atom power connections on motherboard.

Post by apt-e » Wed May 29, 2019 3:57 pm

Hi All,
Some of the caps on my motherboard look a little worse for ware, so I have ordered a replacement set, should be here by the weekend.

See if things improve, fingers crossed.

Thanks all.

Paul

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Re: Acorn Atom power connections on motherboard.

Post by bprosman » Fri May 31, 2019 9:29 am

As they are just used for DC decoupling and not on high(er) frequencies like in a switching power supply I doubt whether this is going to make a huge difference.

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Re: Acorn Atom power connections on motherboard.

Post by etaoin » Sat Jun 01, 2019 6:53 pm

By the way, my own - factory built - Atom (bought mid 80’s) was in storage for years and had similar stability problems. Apart from the recap, I needed to reflow most of the board.

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Re: Acorn Atom power connections on motherboard.

Post by roland » Sun Jun 02, 2019 7:49 am

bprosman wrote:
Fri May 31, 2019 9:29 am
As they are just used for DC decoupling and not on high(er) frequencies like in a switching power supply I doubt whether this is going to make a huge difference.
C4 can make a huge difference. Especially when you have a blurry screen.
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Re: Acorn Atom power connections on motherboard.

Post by bprosman » Sun Jun 02, 2019 9:24 am

Indeed as that is part of the filter but that is the only one. Instead of "recapping" I would more suggest "resocketing".

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Re: Acorn Atom power connections on motherboard.

Post by apt-e » Mon Jun 03, 2019 2:07 pm

Hi all,
Thank you everyone for your input into my Atoms problems.

When time allows, I will recap the board, as there are only a few to do, and I will test and re-socket if need be, again I will keep you all posted.

Thanks again

Paul

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