My new Atom greets me with nothing but P's

discussion of games, software, hardware & emulators relating to the Acorn Atom
error
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My new Atom greets me with nothing but P's

Postby error » Sun Aug 06, 2017 7:32 pm

As per subject -

I've just been given an Atom (so chuffed about that!) but all it wants to do is write the letter P across the entire screen. And I don't like p's at all! :x

If I press BREAK, I am treated to a screen filled with X's

I have a scope, voltmeter, etc - but am not a very technically-minded person; much better at following instructions!

Does anyone have any suggestions on what to check first? I've done the usual reseating and checking for bad joints, but nothing obvious yet. It would be great to see this old thing spring to life again :D

Additional info - it was converted to 5v and is running off a stable regulated PC power supply.

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Multiwizard
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Re: My new Atom greets me with nothing but P's

Postby Multiwizard » Sun Aug 06, 2017 7:38 pm

Hi,

Perhaps the Atom have to P and can't find the loo... :lol:

Anyway, just joking, could you upload a picture of the screen you get?


Greetings, Wim... :-)

error
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Re: My new Atom greets me with nothing but P's

Postby error » Sun Aug 06, 2017 7:52 pm

Ha ha, I should have anticipated that joke :D

I've attached some pics...

Image quality is bad anyway because it's through RF on an LCD TV, hence the smearing (but I have nothing else to compare to)
Attachments
DSC03884.JPG
With Break held down
DSC03883.JPG
Without Break held down

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hoglet
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Re: My new Atom greets me with nothing but P's

Postby hoglet » Sun Aug 06, 2017 8:00 pm

Can you post a hires photo of the inside of your Atom?

error
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Re: My new Atom greets me with nothing but P's

Postby error » Sun Aug 06, 2017 8:06 pm

hoglet wrote:Can you post a hires photo of the inside of your Atom?


Sure - I will do that in the next few days when I can get it laid out on the table 8)

error
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Re: My new Atom greets me with nothing but P's

Postby error » Sun Aug 06, 2017 9:41 pm

OK so I found a few minutes to take some pics, no idea why I assumed this would be an intensive job - it's one of the easiest computers I've ever dismantled! :D , hope these are hi-res enough, my camera has an annoying tendency to try and defocus background objects!
Attachments
ATOM (10).JPG
ATOM (9).JPG
ATOM (8).JPG
ATOM (7).JPG
ATOM (6).JPG
ATOM (5).JPG
ATOM (4).JPG
ATOM (3).JPG
ATOM (2).JPG
ATOM (1).JPG

error
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Re: My new Atom greets me with nothing but P's

Postby error » Sun Aug 06, 2017 9:42 pm

...Aaaaand some more
Attachments
ATOM (13).JPG
ATOM (12).JPG
ATOM (11).JPG

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Multiwizard
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Re: My new Atom greets me with nothing but P's

Postby Multiwizard » Mon Aug 07, 2017 6:00 am

Thanks for aaaalll the pics... :D

I see several suspicious solder points perhaps also even a broken copper track... :(

If I were you I would clean the solder side first firmly and gentle at the same time...

After that you have a much better view what's going on.


Greetings, Wim... :-)

Prime
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Re: My new Atom greets me with nothing but P's

Postby Prime » Mon Aug 07, 2017 6:22 am

Also just to check, what power supply are you running it on?

What is it's output voltage?

Cheers,

Phill.

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martinw
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Re: My new Atom greets me with nothing but P's

Postby martinw » Mon Aug 07, 2017 6:30 am

An early one, with the spring keys too ...

Martin

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oss003
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Re: My new Atom greets me with nothing but P's

Postby oss003 » Mon Aug 07, 2017 8:07 am

First I would also go for a good cleaning of the solder side of the board and making sure the washers in the keyboard area are plastic and not causing any shortcuts. Then taking out the chips, cleaning the legs and reaseating them should be the next step.

Greetings
Kees

error
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Re: My new Atom greets me with nothing but P's

Postby error » Mon Aug 07, 2017 8:58 am

Thanks for the suggestions. I will give it a clean with some isopropyl alcohol and inspect it all again.

The PSU is an older AT PC type, which I'm using rather than ATX because it has the integrated power button. It measures a constant 5.17v with no load, the VCC pins of some ICs measured were approx 4.96v.

The keyboard washers are metal, I did move them away from the tracks but will change these anyway.

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Re: My new Atom greets me with nothing but P's

Postby Prime » Mon Aug 07, 2017 10:42 am

error wrote:Thanks for the suggestions. I will give it a clean with some isopropyl alcohol and inspect it all again.

The PSU is an older AT PC type, which I'm using rather than ATX because it has the integrated power button. It measures a constant 5.17v with no load, the VCC pins of some ICs measured were approx 4.96v.


That should be fine, just wanted to check that you where not using the original Atom PSU (which outputs 8V IIRC), as the voltage regulators have been bypassed (actually it looks like they have been removed completely!

Cheers.

Phill.

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roland
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Re: My new Atom greets me with nothing but P's

Postby roland » Mon Aug 07, 2017 1:04 pm

This Atom has had a tough youth if I look at the area around the voltage regulators. But I think we can bring it back to life again. You already did a few basic steps: reseating the ic's and check the voltage. Some next steps are:

Does the Atom beep if you press CTRL+G ?

If so (but I don't think it will) then the problem is in the video ram. Remove all the 2114's and just place two known good 2114's in sockets 42 and 43 (those are the ic's that hold the text screen. If that solves the problem then you have to figure out which 2114's are faulty.

The problem is not in the video ram, it is probably that the Atom is not starting or completing its reset routine. One of the first steps it does is initializing some workspace in the first 1 kB of memory space. (ic 51 and 52). Then it sets up the 8255 and clearing the screen and displaying its ACORN ATOM text. As the screen is not cleared, something goes wrong in the first step.

- is there a clock signal for the 6502? Check pin 37 (Ø0 = Clock in) and pin 39 (Ø2 = Clock out). Both pins should have a 1 MHz square wave.

- is the a 60 Hz signal on pin 10 of the 8255? If not, is there a 60Hz on pin 37 of the 6847? If yes then you have a bad track between those pins, if not, is there a 3.58MHz signal on pin 33 of the 6847?

- Is the processor running? You might detect some activity on address line A0 (pin 9) of the 6502 and perhaps also on the data bus (pin 20 - 33 of the 6502). Also check the R/W on pin 34 of the 6502. If these are alternating, the cpu is probably busy doing something.

- And then also worth to check: are the IRQ, NMI and RST lines tied to a voltage > 3V? RST will be low during pressing the BREAK key but IRQ and NMI will always be "high" in an unexpanded Atom.

If all these (clock) signals are correct, the problem will be in the zero page ram, the MOS ROM (IC 21) or the addressing of these memory chips.

Looking forward to see the results of those tests.

Greetings,
Roland
256K + 6502 Inside
MAN WOMAN :shock:

Prime
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Re: My new Atom greets me with nothing but P's

Postby Prime » Mon Aug 07, 2017 2:03 pm

roland wrote:- is the a 60 Hz signal on pin 10 of the 8255? If not, is there a 60Hz on pin 37 of the 6847? If yes then you have a bad track between those pins, if not, is there a 3.58MHz signal on pin 33 of the 6847?


As he's getting a picture I would say the clock to the 6847 is OK, as there would be nothing at all on the screen if it where not working.

Cheers.

Phill.

error
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Re: My new Atom greets me with nothing but P's

Postby error » Fri Aug 11, 2017 9:27 pm

Thanks for all the tips, I will try some of these this weekend.

(No beeps though - no speaker!)

Does anyone know which screws are meant to be with this case? The ones I have surely can't be right, they look more like wood screws?

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oss003
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Re: My new Atom greets me with nothing but P's

Postby oss003 » Sat Aug 12, 2017 9:56 am

The Atom Technical Manual says: 'Four short and two long self-tapping screws.'

In my Atom the short ones are diam.3,5 mm with length 10mm en the long ones diam.4 mm with length 40 mm.
They both have rounded cross heads and the short ones are mounted with isolating washers.

Greetings
Kees
Attachments
screw.png

error
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Re: My new Atom greets me with nothing but P's

Postby error » Sat Aug 12, 2017 7:58 pm

Thanks Kees! That looks much more like what I imagined they should look like :D I will dig around for something suitable :)

I reflowed much of the solder points this morning (as much for aesthetics than anything else), and now it behaves slightly differently.

It still doesn't boot, however, it now produces a random screen each time I press break.

So the screen full of P is now replaced by things like: screen full of X, screen full of @, random jumbling, random blocks, screen full of z, screen full of 1 (you get the picture... it will show many different repeated screens across the character set). It's kind of like playing a one armed bandit where you always lose. I think I gave up after the 200th time of pressing Break. Small crumb of comfort - the break key works! :mrgreen:

I need to clear some space so I can properly analyse the pins with my scope as mentioned in the previous posts. My iron is easier to dig out without incurring the wrath of Mrs Error :lol:

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Re: My new Atom greets me with nothing but P's

Postby JamesD » Tue Aug 15, 2017 3:04 pm

The solder job on the red wire looks bad. The wire fans out way too far.
There are a lot of suspicious looking solder joints.

The CPU is obviously trying to change video RAM, so it's probably good.
The video RAM contents are clearly changing. I usually see some constant characters in some places if it's bad video RAM, but it still might be the problem.
I see lots of noise in the video like video data or address lines are constantly being accessed by the CPU during video refresh.
Is that normal?
The CPU seems to be able to change at least the bottom 12 address lines or it couldn't write to the entire screen RAM.
I can't remember what address video RAM is at, but if it's in the lower 32K, then the CPU can probably change at least 13 address lines.
ROMs can certainly go bad, but I'd think it wouldn't get that far. No promises though. I know EPROMs can be partially erased.

I'd check to see if any data lines are stuck high or low, and I'd see if any video chips are hot.
Then I'd check solder joints on the data buss lines.

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roland
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Re: My new Atom greets me with nothing but P's

Postby roland » Tue Aug 15, 2017 10:40 pm

The Atom video ram starts at #8000 and uses 512 bytes for text mode. So that ends at #81FF. The. Total video memory ends at #97FF (clear 4 graphics mode). However the complete memory from #8000 to #9FFF is decoded within the video memory area and might cause distortion of the video display when the cpu accesses this memory.
256K + 6502 Inside
MAN WOMAN :shock:

JamesD
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Re: My new Atom greets me with nothing but P's

Postby JamesD » Wed Aug 16, 2017 4:55 pm

JamesD wrote:The solder job on the red wire looks bad. The wire fans out way too far.
...
I'd check to see if any data lines are stuck high or low, and I'd see if any video chips are hot.
Then I'd check solder joints on the data buss lines.

That was supposed to say RAM chips.


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