Amiga 600 - weird video problem

[Drakon]

Hi all.
Has anyone a problem with video as pictured on the photo? I've buyed A600 (rev. 1.5) in a very bad condition, recapped it, cleaned and so on. Also, i've removed the RF modulator.
When Workbench loads, part of icons from left appeared on the right side with weird colors. Amiga is equipped with Furia 020 and original KS from Cloanto (3.1).

Any clues what to check? This is a photo with RGB cable connected, but on RCA the picture is the same.

[Amiga1992]

You forgot to attach the photo.

Was there massive cap leakage in the area near the power connector? If so, maybe the video encoder got damaged.

[Daedalus]

Hmmm, that looks very odd. It's not the typical fault from leaking capacitors beside the video encoder - the picture is sharp but wrapped around slightly, and looks like it's reading from RAM incorrectly. It could be some sort of issue with the pixel clock, or maybe some sort of graphics patch or funky display mode that's causing it. What happens if you boot from floppy with a Workbench disk? Does it do the same? What are the screenmode and overscan settings? What is in the DEVS:Monitors drawer?

[Drakon]

Well nope, there wasn't a leakage. Capacitors were old, but they not leaked.
@Daedalus: will test it today and post a result. Screenmode is 640x256 x 16 cols.

[Amiga1992]

Originally Posted by Daedalus

Hmmm, that looks very odd. It's not the typical fault from leaking capacitors beside the video encoder

Agreed, looks like corrupted RAM.

[Drakon]

If this helps, i have a 1MB expansion under the trapdoor, but Amiga won't recognize it. With, or without it inserted, the chipmem size is the same.

[Amiga1992]

And it still does this problem when it's disconnected, right?

[Drakon]

Yes, exactly.

[MigaTech]

Does it show this on all other display screen mode options? Try changing screen modes. Does it happen when the Amiga switches to 15.1KHz game mode?

Have you tried a different monitor? Probably is bad RAM.

[Daedalus]

Yep, or damage to Agnus or the motherboard that's causing RAM bus issues...

[Drakon]

Allright folks. Computer tested with DiagROM. All RAM, CIAs and so on are ok. Furia also is fine. Tried with other kickstarts. The problem with screen didn't appears in KS1.3. On 2.x, 3.x the damned thing still happens.
I have just (?) one issue - the PCMCIA port is not visible at all. Even in boot menu it didn't apears. Any clues? Is Gayle gone (but, the IDE port works fine). Can this faulty PCMCIA and video problem be related?
Problem appears in all screen modes. In games, demos, i didn't notice it, just in Workbench. Also, i've launched ProTracker 3.62 and the screen is fine.

[Toni Wilen]

This kind of corruption can only have single reason: Screen horizontal stop is not having any effect (DIWSTOP register) or wrong value gets written to DIWSTOP.

KS2.0+ use slightly different screen setup than KS 1.x, which causes "wrap around" effect which is normally hidden. (Wrong colors are due to mismatched bitplanes, it is "normal")

One possible reason is damaged Denise. (or perhaps also Agnus)

[Drakon]

Well, Toni, but can this be related with disappeared PCMCIA? There is no CC0: even in Boot Menu.

[Toni Wilen]

Originally Posted by Drakon

Well, Toni, but can this be related with disappeared PCMCIA? There is no CC0: even in Boot Menu.

No, at least not directly. (PCMCIA is handled by some buffer chips and Gayle).

Perhaps the graphics issue has always been there but no one has noticed or cared about it? (I can't see how any mainboard damage could cause it without causing other much more worse side-effects)

[fordav1]

Originally Posted by Drakon

If this helps, i have a 1MB expansion under the trapdoor, but Amiga won't recognize it. With, or without it inserted, the chipmem size is the same.

I have fixed a few A600's with exactly that problem, where the expansion RAM is not seen. The problem is caused by open vias caused by leaking SMD electrolytic caps. Trace all the pins from the expansion connector to the end (using schematics) and you will find at least one that is not connected.
A similar thing can happen to the PCMCIA slot when SMD caps near the power connector leak and the electrolyte gets under the 44 pin HDD connector. I have fixed a few that lost the DH0: and CC0: as well. It's exactly the same fault. The tracks under the 44-pin IDE connector go to some logic chips just near there and any open vias or broken tracks will cause loss of CC0:
To fix that you ideally should remove the poor quality 44-pin IDE connector and trace all the lines to the end. You will probably find the 44-pin connections are ok but the traces that go to the holes will be broken right where the trace meets the hole. I have seen that **A LOT**.... very very common. After fixing the problem replace the 44-pin IDE connector with a better quality type that has an outer shroud around it which allows easier plugging of the cable or CF>IDE adapter
FYI, most problems in A600/A1200 are due to open vias or broken tracks at the solder pad/hole caused by leaking caps.