1040ST and internal Floppy drive grounding prob?

[tjlazah]

I am trying to resurect this Atari 1040ST I have. It worked but the video was really bad on a cold boot. Screen flipped and was unusable for about 10 minutes, then as it warmed up it got better but still was a bad video signal. I tried to get it working by reseating all chips etc and no go. I swapped all socketted chips and no go. I though, well I will just get another cheap system board! I did and both exibited a similar problem. On disk loading, each track load, or click from drive, would flip or jump the screen, but it was clear and crisp unlike original board. Also as unit warmed up from cold boot it would get less evident but still on disk loads the screen would flip or jump slightly. One thing I noticed is the drive standoffs were glued on the motherboard since the replacement boards did not have them on. The brass one was also glued on, does this need to be grounded to the board? ie no glue! I cannot see what the problem might be, I tried two different PS's.

[+Mitch]

Have you tried a different monitor?

 

Mitch

[Gunstar]

I am trying to resurect this Atari 1040ST I have.  It worked but the video was really bad on a cold boot.  Screen flipped and was unusable for about 10 minutes, then as it warmed up it got better but still was a bad video signal.  I tried to get it working by reseating all chips etc and no go.  I swapped all socketted chips and no go.  I though, well I will just get another cheap system board!  I did and both exibited a similar problem.  On disk loading, each track load, or click from drive, would flip or jump the screen, but it was clear and crisp unlike original board.  Also as unit warmed up from cold boot it would get less evident but still on disk loads the screen would flip or jump slightly.  One thing I noticed is the drive standoffs were glued on the motherboard since the replacement boards did not have them on.  The brass one was also glued on, does this need to be grounded to the board?  ie no glue!  I cannot see what the problem might be, I tried two different PS's.

948528[/snapback]

 

Yes, that is the whole point of the brass "standoff," It is supposed to be metal-to-metal for ground, so if there is glue in between the brass "standoff" and the metal pad it is supposed to make contact with, that glue should be removed. If it is loose without the glue, then the best thing to do would be to put a spot of solder or two there to hold it in place so that it is properly grounded. Whether this will solve your problem with the flipping screen, I can't say for sure, but if it happens when the drive is accessing, then there is a good chance that this is the case. It wouldn't hurt to make sure that the monitor is properly grounded too, it could be that the ground wire from the power cord has come loose or has a "cold" solder point.

[tjlazer]

I have tried several monitors and they all do the same thing. I will try to ground the floppy and see if that helps... Thanks for the inputs.

[javiero]

I think the problem might be the big capacitor in the power pack, i think 2200uF

200 Volt. Just exchange it and it will be fine.

[+remowilliams]

I've seen this problem to a lesser extent on many of the classic computers, not just the STs. I've got an A500 an an ST around that exhibit a bit of the stepper motor video signal dimming.

Edited October 21, 2005 by remowilliams

[tjlazah]

I grounded the floppy to the motherboard and it did not help. Must be the PS, I have two and they both do the same thing.