Strange problem with DaveH's Atom.

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Prime
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Strange problem with DaveH's Atom.

Post by Prime »

Just fitted the new colour board and RAMROM to Dave H's issue 4 Atom.

Everything is working except 1.7MHz mode which just hangs.

I've checked the CPU, 8255 and LS393 in one of my machines and they work fine. I've also checked the wire links on Dave's board several times and they agree with my working board. The RAMROM works as it should in my machine.

Not sure what could be causing this :(

Anyone have any suggestions?

Cheers.

Phill.
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hoglet
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Re: Strange problem with DaveH's Atom.

Post by hoglet »

Has it ever been clocked beyond 1MHz before you fitted these board?

What's the CPU exactly?

At what point is it hanging?

Dave
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oss003
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Re: Strange problem with DaveH's Atom.

Post by oss003 »

Maybe the speed of the video RAM?

Kees
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1024MAK
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Re: Strange problem with DaveH's Atom.

Post by 1024MAK »

Is this a nuclear game of hangman :?:

Guess which bit is being a bit slow, and if we don't get it in time, the Atom dies...Kaboom! :shock:

Mark
Last edited by 1024MAK on Sat Nov 21, 2015 2:41 pm, edited 1 time in total.
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TheCorfiot
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Re: Strange problem with DaveH's Atom.

Post by TheCorfiot »

As Dave H suggests, I would swap out the CPU and just to be sure check on the board mods for the RAMROM board.

:)
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hoglet
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Re: Strange problem with DaveH's Atom.

Post by hoglet »

Was there an happy ending to this story?

Dave
Prime
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Re: Strange problem with DaveH's Atom.

Post by Prime »

hoglet wrote:Was there an happy ending to this story?
Well machine will still only run at 1MHz, but Dave was happy with that for the time being. I've asked him to re-cap the board as people seemed to think that was deffo a good idea and could be causing the problem.

6502 was a 1MHz rated 6502, but it ran fine in my test board at 1.7MHz, and we also tried the 6502A from my machine in Dave's board.

I've left it that if it still mis-behaves after the re-cap I'll have another look at the next meetup.

Cheers.

Phill.
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oss003
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Re: Strange problem with DaveH's Atom.

Post by oss003 »

Was the CPU also hanging or just no display?

Maybe test it with an assembler program to beep to hear if the processor is still running.
P=#2800;[JSR#FD1A;JMP#2800

Kees
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Re: Strange problem with DaveH's Atom.

Post by Prime »

oss003 wrote:Was the CPU also hanging or just no display?

Maybe test it with an assembler program to beep to hear if the processor is still running.
P=#2800;[JSR#FD1A;JMP#2800
Well it *seemed* to be running when I poked it and the RAM / ROM with a scope. Though hitting ^G didn't generate the normal beep, so maybe it's getting stuck before getting there.

Cheers.

Phill.
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Re: Strange problem with DaveH's Atom.

Post by oss003 »

When you are in command mode, it's possible that the Atom hangs on waiting for a flyback.
When running the MC code, there is no waiting for flyback.

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Kees
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daveejhitchins
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Re: Strange problem with DaveH's Atom.

Post by daveejhitchins »

An update to this Atom issue:

I've recently decided to sell this Atom - The reasons are: I've not used it :oops: and at some time during the next 12 months we will be moving house to somewhere on the South Coast - so the less I have to pack the better - I most likely won't have such a large workroom :?

So . . . As there is interest in this Atom, I decided to spruce it up a little. I've replaced all but the reset Electrolytic capacitors, all the 47n ceramics to 100n and replaced any white IC socket, that is in-use, with turned pin versions.

The 1.7MHz mode is working fine now :D However, I'm seeing this problem - (starts at 1MHz switching to 1.7MHz then back to 1MHz). I'm waiting for a reply from Phill to see if there is a CPLD update. The board version is: 5.10c (not sure of the .jed file version that it has).

Dave H.
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Re: Strange problem with DaveH's Atom.

Post by daveejhitchins »

I've fixed the problem with this colour board.

First was to update the CPLD - That 'nearly' fixed it - the frame glitch now only occured in slow mode.

Out with the 'scope. First I checked the +5V supply - reading good, however, there was excessive AC noise! Well over 2V PP :shock: and even more in bursts that seem to be synchronised with the frame pulse.

The fix was: Add 100n and a 10u tantalum bead under the 6847 (there was unpopulated positions for them). Next - the colour board uses one pin from IC42 on the main atom board, however, connects with the whole right hand row of that IC. As the contacts were sloppy I replaced it with a turned pin socket. Then I connected a link, on the colour board, from what would be the +5V supply to IC42, to the +5V supply on the colour board. And, finally, added a second 10u tantalum bead near to the 3V3 regulator. See photos.

The scrolling is now rock solid.

this may be useful for anyone else having similar problems. The colour board version is 5.10c.

IMG_1202.jpg
IMG_1203.jpg

Dave H.
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