Atari 800xl problem (black screen and upramping tone/sound)

[cerror]

The photo that DrVenkman posted of the U1MB reset fix is correct, but the value of the capacitor should be 100pf.

 

- Michael

Crap, just missed this.

You think the 1nf will work as well?

 

I got it from: http://atari8.co.uk/wp-content/uploads/2016/12/Ultimate-1MB-and-Incognito-BIOS-and-XEX-Loader.pdf(page 7)

[_The Doctor__]

another fine example of what should be added to the installation outline of the product...

[cerror]

another fine example of what should be added to the installation outline of the product...

Well the weird thing is: it worked fine before the whole stereo debacle...

But you got a point.

 

I'll keep ya'll updated!

[_The Doctor__]

The correct thing to do is fix the damaged reset circuit in the Atari(if it has been) or if there were damage to the U1M that is introducing noise, but the 'fix' works well enough

Edited May 6, 2017 by _The Doctor__

[+mytek]

Crap, just missed this.

You think the 1nf will work as well?

 

I got it from: http://atari8.co.uk/wp-content/uploads/2016/12/Ultimate-1MB-and-Incognito-BIOS-and-XEX-Loader.pdf(page 7)

I would trust what Jon is saying to do in that document, although that is a big change of several magnitudes going from 100pf up to .1uf (1nf). Obviously the noise problem turned out to be much worse requiring additional filtering (looks to be not so much a noisy reset line but more like an occasional voltage spike that gets imposed onto this line). I don't think it's actually a fault with the Atari reset circuit, but something being overly sensitive in the U1MB itself. And having a wire connection of several inches long certainly doesn't help matters, acting like an antenna.

 

- Michael

Edited May 7, 2017 by mytekcontrols

[Joey Z]

...although that is a big change of several magnitudes going from 100pf up to .1uf (1nf).

actually .1uF = 100nF, 1nF is only 1 order of magnitude greater than 100pF (.1nF) so this is probably fine.

[cerror]

I would trust what Jon is saying to do in that document, although that is a big change of several magnitudes going from 100pf up to .1uf (1nf). Obviously the noise problem turned out to be much worse requiring additional filtering (looks to be not so much a noisy reset line but more like an occasional voltage spike that gets imposed onto this line). I don't think it's actually a fault with the Atari reset circuit, but something being overly sensitive in the U1MB itself. And having a wire connection of several inches long certainly doesn't help matters, acting like an antenna.

 

- Michael

 

actually .1uF = 100nF, 1nF is only 1 order of magnitude greater than 100pF (.1nF) so this is probably fine.

 

I orderded the 1nf, but I am going to get a 100pf as well. Just to be sure.

[+mytek]

As you can tell I don't use 'nf' values in what I normally do so I apologise for my mistaken notion that this was equivalent to .1uf (I knew those math classes that I skipped in school would catch up to me someday). Yes .001uf (1nf) should be fine, whereas .1uf (100nf) would probably create too much of a slope in the reset signal perhaps adversely affecting other chips that are tied into this same line.

 

- Michael