800XL with duff SIO

[svenski]

I've got an 800XL with faulty SIO. Connected it to SIO2USB and worked fine - booted up disk image then it reset and now nothing. Initially the XL would give a static sounding noise then go straight to READY, now it goes through the motions again of looking for a connected drive but won't recognise them. Can't see anything blown on the board, audio and keyboard still work fine and RAM checks OK.

 

The SIO2USB detects the computer turning on as there is activity on the SIO2USB board. The SIO2USB works fine when connected to another Atari.

 

The 800XL had been working fine but I'm not going to blame the SIO2USB at this stage - I'm guessing there was an existing problem. Anyone have any ideas? Rev D board.

[Marius]

I've got an 800XL with faulty SIO. Connected it to SIO2USB and worked fine - booted up disk image then it reset and now nothing. Initially the XL would give a static sounding noise then go straight to READY, now it goes through the motions again of looking for a connected drive but won't recognise them. Can't see anything blown on the board, audio and keyboard still work fine and RAM checks OK.

 

The SIO2USB detects the computer turning on as there is activity on the SIO2USB board. The SIO2USB works fine when connected to another Atari.

 

The 800XL had been working fine but I'm not going to blame the SIO2USB at this stage - I'm guessing there was an existing problem. Anyone have any ideas? Rev D board.

 

Any chance the PSU of your atari is bad?

 

Sio2USB is asking definately some current, and I think bad PSU's are a pain in the ass anyway.

 

give it a try...

[Marius]

Is the SIO buffered?

 

I thought it wasn't... but if it is it might be a blown buffer chip, they are weak.

 

Can you swap pokey?

 

Just a few ideas...

[svenski]

Marius, can you tell me which is the buffer chip?

 

The PSU works fine with another XL and XES so I doubt that would be the problem.

 

I can try swapping the POKEY chip and see if that helps but the spare XL I have here has POKEY issues - keyboard and low sound but it does work fine with the SIO2USB.

[Rybags]

No buffering occurs on the SIO lines but there are resistors and capacitors along the path that might potentially go bad.

 

Not sure what the best approach could be. You could measure the voltage levels with a multimeter for starters, we'd have to give you some Basic commands that would force 0 or 1 output on the Command and DataOut lines.

 

A loopback test might be another thing to try. Hooking the Data and Command lines to a joystick port would allow test signals to be sent/received, but I have no idea if any software exists to do this... maybe the SALT cartridge?

[svenski]

Thanks for the replies guys. I did some digging that suggests it could be PIA related and Bradley at Best Electronics has suggested to try and swap out PIA as well - as a lot of the SIO connector J1 functions go through PIA - so will give that a go. I'll post here if I get a result.

 

Also, for anyone looking to order from Best before Christmas, I suggest you do it quick as they are working around the clock at the moment!

[Rybags]

Definately possible - PIA handles the COMMAND line and without that SIO compliant devices won't respond at all.

[svenski]

Well I'm having some fun trying to turn two faulty 800XLs into 1.

 

The first has a keyboard and sound problem - half the keyboard doesn't work and sound output is extremely low.

The second seemed to lose its SIO after running it briefly with SIO2USB.

 

I swapped keyboards and got the same result on the first XL. I was going to swap PIA chips but on the second XL (the one with no SIO) PIA is soldered - a REV D board. I decided to swap POKEY and hopefully get the first machine (the one with kb and sound problems) working - this machine has no SIO issues.

 

There was no change whatsoever to the first machine - it still has sound and keyboard issues and SIO continues to work.

 

On the second, where I added what I presumed to be a faulty POKEY chip, keyboard and sound are fine as before but now SIO is back to life!

 

So, as you can guess I'm scratching my head a fair bit here

[Rybags]

If the keyboard is faulty, it might be one of the two multiplexor ICs where the problem is originating (of course first rule out that it's not the common mylar underlay problem).

 

On the XL there should be 2 identical small ICs near where the ribbon plugs in. If you swap them over and the nature of the problem changes then it's almost definately one of them at fault.

 

PIA has no direct relation to the keyboard so shouldn't make a difference one way or the other.

Edited December 18, 2010 by Rybags

[svenski]

If the keyboard is faulty, it might be one of the two multiplexor ICs where the problem is originating (of course first rule out that it's not the common mylar underlay problem).

 

On the XL there should be 2 identical small ICs near where the ribbon plugs in. If you swap them over and the nature of the problem changes then it's almost definately one of them at fault.

 

PIA has no direct relation to the keyboard so shouldn't make a difference one way or the other.

 

Thanks, I'll try and give that a go.

 

SIO has stopped again on the second after a brief spurt of life. Have tried different PSUs with no difference. Can't work out why it would come to life again briefly, I'm presuming there must be a short or bad contact somewhere.

[Rybags]

If possible, test SIO using a real 1050 or other physical drive... just to rule out possible problems at the emulation side.

[svenski]

If possible, test SIO using a real 1050 or other physical drive... just to rule out possible problems at the emulation side.

 

Hi,

 

Tried that. When the SIO works it will load via the SIO2USB or without it - with a drive connected directly.

 

Thanks for your advice so far, will keep experimenting !