A. Baldwin Dot Crawl Suppressor

Renegade

Just found this:

http://www.worldofspectrum.org/infoseekid.cgi?id=1000622

What the heck was that modification...? :p

It sounds good, but did it work? :D

Anybody has any information on what this could be?

RobeeeJay

Renegade wrote: »

Just found this:

http://www.worldofspectrum.org/infoseekid.cgi?id=1000622

What the heck was that modification...? :p

Two solder joints? My guess is just a couple of capacitors in parallel. I thought the big problem with the dot crawl was down to not having enough dedicated crystals so some of the video carrier waves were off?

mcleod_ideafix

Dot crawl happens when the pixel clock is not in phase with color burst clock, which is the case with the Spectrum 48K, as pixel clock is generated by a different crystal than the color clock. Later 128K models generate all clocks from the same crystal, so all of them are in phase and no dot crawl (or very little) happens.

Renegade

"Is your shakin speccy driving you dotty?" (check)

"Does it shimmer and shake, like a snake?" (check again)

"Do colors slide, and crawl to the side?" (and again)

"Will you pay for a firmer, sharper display?" (WHAAAT???) :p


He who promises that much must deliver results! :-o

Mr. A. Baldwin, I want to know your secret!!! :p :D

Tell us, what did you find that we all have missed?! :rolleyes:

RobeeeJay wrote: »

Two solder joints? My guess is just a couple of capacitors in parallel. I thought the big problem with the dot crawl was down to not having enough dedicated crystals so some of the video carrier waves were off?

Even if the mod was down to a couple of capacitors were would those be placed?

RobeeeJay

Renegade wrote: »

Even if the mod was down to a couple of capacitors were would those be placed?

At a guess between the signal in to the modulator, and ground. Or perhaps somewhere in the video circuitry that combines the outputs from the ULA into a composite-esque feed.

There aren't many other things you can do with just two solder joints. You could put something in parallel, but I can't think of anything useful you could do with that.

1024MAK

I do know of a way to completely eliminate dot craw. No new components are needed. Of course, there is a downside, you also loose the colours....:p

Maybe it was just a ceramic disc capacitor that was soldered in one of the oscillator circuits, thus shifting it's frequency slightly. Not a fix, just a bodge to change the symptoms...

Mark