A1200 display noise issues

Jolly · 17 June 2021, 21:30

I experience some display noise on my A1200 in 31khz modes that very closely matches the symptoms described here:

https://rastport.com/techblog/removi...splay-trashes/

I just had the machine recapped so that is not the issue.

The article above suggest a "soft fix" by adjusting palette values - this works very well reducing the problem almost to zero.

The article also suggest a hardware mod based on shorting resistor E127R (LP filter on CCK). If this works it is a lot more convenient than having to manage palettes.

As I have not found this fix described elsewhere I would like to know if anyone on this forum has experience with this before giving it a go. Anyone?

Krashan · 20 June 2021, 19:26

Quote:

Originally Posted by Jolly

As I have not found this fix described elsewhere I would like to know if anyone on this forum has experience with this before giving it a go. Anyone?

I do, but as I am the author of the aforementioned article, I probably do not count ;-) Anyway it still works great with my 1D4 mainboard.

Jolly · 21 June 2021, 21:10

Quote:

Originally Posted by Krashan

I do, but as I am the author of the aforementioned article, I probably do not count ;-) Anyway it still works great with my 1D4 mainboard.

I can come back here with the blame in case it doesn't work then

Will give it a try within the coming weeks when I have a quiet day - and report back here how it turned out.

It is a rev 2 motherboard.

Jolly · 20 July 2021, 22:23

I finally got around to implementing the mod and can report that it works great

All symptoms have disappeared and there is no need to manage palettes any longer

Thanks @Krashan for the blog-post linked above!

DarrenHD · 21 July 2021, 16:50

Quote:

Originally Posted by Jolly

I finally got around to implementing the mod and can report that it works great

All symptoms have disappeared and there is no need to manage palettes any longer

Thanks @Krashan for the blog-post linked above!

Great news. BTW, do you have any photos of these "display" trashes?

Jolly · 21 July 2021, 22:05

I did not think to take pictures/movies, but there is another thread that links to a video, see http://eab.abime.net/showthread.php?t=107514. My problems were similar, but less severe.

Jpor · 28 July 2021, 15:52

Have done that hack myself as well as place heatsinks on the Alice chip. Ideal fix for the Indivision flicker/scandoubler to fix image tears.

17 June 2021, 21:30	#1
Jolly Registered User Join Date: May 2021 Location: Arden, Denmark Posts: 10	A1200 display noise issues I experience some display noise on my A1200 in 31khz modes that very closely matches the symptoms described here: https://rastport.com/techblog/removi...splay-trashes/ I just had the machine recapped so that is not the issue. The article above suggest a "soft fix" by adjusting palette values - this works very well reducing the problem almost to zero. The article also suggest a hardware mod based on shorting resistor E127R (LP filter on CCK). If this works it is a lot more convenient than having to manage palettes. As I have not found this fix described elsewhere I would like to know if anyone on this forum has experience with this before giving it a go. Anyone?

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20 July 2021, 22:23	#4
Jolly Registered User Join Date: May 2021 Location: Arden, Denmark Posts: 10	I finally got around to implementing the mod and can report that it works great All symptoms have disappeared and there is no need to manage palettes any longer Thanks @Krashan for the blog-post linked above!

21 July 2021, 22:05	#6
Jolly Registered User Join Date: May 2021 Location: Arden, Denmark Posts: 10	I did not think to take pictures/movies, but there is another thread that links to a video, see http://eab.abime.net/showthread.php?t=107514. My problems were similar, but less severe.

28 July 2021, 15:52	#7
Jpor Banned Join Date: Feb 2019 Location: United Kingdom Posts: 404	Have done that hack myself as well as place heatsinks on the Alice chip. Ideal fix for the Indivision flicker/scandoubler to fix image tears.

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