ATARI 1040 STe black RGB good Composite

[zChris]

Hello!

I have acquired a Atari 1040STe. It has the "won't start unless pressing the reset switch" issue which i plan to fix in the future. The biggest issue though is that there is no signal on RGB although composite works as it should.

Also found a mod(or from factory?) that im curious on if someone can identify what it does ?

20220418_163646.jpg

motherboard revision is CA4003290

/zChris

[exxos]

Factory bodge.

[rubber_jonnie]

Factory bodge.

+1 for this, the really white 'hot snot' is generally a factory fix.

I have seen this bodge before, but sadly I can't recall specifically what it does.

[zChris]

Also notice that the chips to the left are piggybacked!

[Steve]

Yeah all you gotta do is have a browse in the motherboard photos section on the forum and you'll see that any 'older' models of the STe all are like this.

In regards to your no RGB output I wonder if that might have something to do with the R G B transistors near the shifter, or if they were faulty would that affect the composite output too? I don't know.

[zChris]

Hello,

There seem to be a broken trace or something similiar on this board. If i have the board flat on the table and boot it up it works (still no RGB though), but if i lift up the right side so the board makes a small arc it shutsdown. I have the exxos PSU and when measuring the red i get 0v when it is in this state. When i put it down again it boots up and i get voltage. Does this indicate that there is a short on the board somewhere ? Can take a video later on if that helps.

/zChris

[rubber_jonnie]

Hello,

There seem to be a broken trace or something similiar on this board. If i have the board flat on the table and boot it up it works (still no RGB though), but if i lift up the right side so the board makes a small arc it shutsdown. I have the exxos PSU and when measuring the red i get 0v when it is in this state. When i put it down again it boots up and i get voltage. Does this indicate that there is a short on the board somewhere ? Can take a video later on if that helps.

/zChris

Whilst a broken trace or cold joint is a possible explanation, I have also run into something else that is a very quick thing to check.

I had a Mega that was intermittently going off and it was the FDD power cable that was the problem. Flexing the board or moving the FDD caused the machine to go off. The problem was that where the FDD power cable went into the mainboard, it had freyed and whiskers of the 5v line were shorting to ground. It was difficult to see without magnification.

It may not be your problem, but it is really easy to check, you'd be surprised how easy that cable can become freyed.

Easy to resolve by desoldering the cable, chopping off the last 10mm and resoldering fresh.

Worth the 2 minutes it takes to check.

[zChris]

Thanks for the tip rubber_jonnie but it doesn't seem that was the issue. I wiggled the cable around while it was on but nothing happened. I then took the ram out and reseated it and now it doesn't do what i described in the first post.

But i found this on it. A bodge wire from Vcc to 1a is what i got from trying to read the schematics. Seems to be correct. Don't know what that cheap does though? was hoping it might be the cause of RGB not working :)

20220425_201233.jpg

2022-04-25_20-26.png

2022-04-25_20-28.png

[exxos]

For fear of stating the obvious, just to confirm your not using MONO / VGA adapter are you ? As if your in MONO mode.. you won't likely get RGB anyway.

[zChris]

With me nothing is obvious :lol:

I'm using UBE Switch if that helps? What do that mod do anyway?