1040 STE Bussed Resistor Upgrade Fails...

[teQnotic]

So I replaced the bus resistors on my 1040 STE (CA4003290) mainboard and all I get now is a white screen. Any ideas what may have gone wrong?

P101
P102
P103
P104
P105
Changed to 2.2K (9-pin Bussed Type) as recommended

P100
At 1.2K

I checked all pins for continuity and all checks out. I will try reverting back to the original values

[Steve]

When removing bus resistors it's extremely easy to break traces. I always recommend fitting sockets rather than directly fitting new resistors. This allows you to experiment with different values and also reduces the chances of breaking them again if you have to remove/resolder different values.

No joke though, 9 times out of 10, when there's a post like this it always turns out to be a broken trace. When you remove the bus resistors they literally should 'fall out' with zero resistance, if there was any resistance at all you probably have a broken trace. The easiest way of removing them is by just applying a lot of flux and solder, run the iron up/down the pins fast, the SIL literally just drops out with zero force.

(I do realise you said that you tested all the pins. All I can suggest is remove them all, double check every trace, then install sockets. Also make sure you get the orientation right)

[DoG]

Check between VCC and each data line and address line that you have 2.2Kohm. It could also be a solder bridge between traces/pins or trace for VCC be missing on a resistor pack. So check that each pack has 5V.

[rubber_jonnie]

So like @Steve suggested, broken traces are a major possibility, but there is also a possibility of broken vias so it's important to confirm that there is continuity from one side of the board to another, if required, where you've been working.

The other possibility is a short between the pins of the SIL resistors, so i'd suggest a check of that too. Use a magnifying glass or microscope to do a visual, if you don't see anything then use a multimeter.

I have also had a cracked SIL before, so check from pin 1 to all the other pins for the correct resistance of each item.

Also check that the dot on the SIL matches the marking on the board, which is usually a square. They don't work the wrong way round. BTW, I assume you understand this, but mention it because I have seen this done before, mistakes happen.

[teQnotic]

Thank you for all your suggestions. I will double check continuity and will also install header pins so I can try different values

[teQnotic]

Turns out when I did continuity checks on the traces, the break was very close to the SIP pad that it checkout as good, but actually I was touching the broken trace.
Got it working 🙌🏼
What a mess I made though.
Was going to include a photo, but don't know how.

Thanks again! This is a very supportive group

[rubber_jonnie]

Turns out when I did continuity checks on the traces, the break was very close to the SIP pad that it checkout as good, but actually I was touching the broken trace.
Got it working 🙌🏼
What a mess I made though.
Was going to include a photo, but don't know how.

Thanks again! This is a very supportive group

Glad you're working again, these boards can be a bit fragile.

To add pictures, use the attachments tab to upload an image to the site, then use the option to place it inline to add it to your text. It will add where the cursor currently is.

[teQnotic]

20250123_185819.jpg

I was thinking of wiring 2 female 9-pin connectors for P102 & P103 to the blitter chip contacts. This way I can clean it up a bit and have the choice of swapping resisitor packs

[rubber_jonnie]

20250123_185819.jpg

I was thinking of wiring 2 female 9-pin connectors for P102 & P103 to the blitter chip contacts. This way I can clean it up a bit and have the choice of swapping resisitor packs

Glad to see you have the picture uploads sorted out.

From my perspective I'd probably leave it as you might end up causing more problems.

However if I did a re-do I would do it on the underside of the mainboard as it means less hassle if you do decide to fit sockets for the SIL resistor packs. It also means the topside looks standard.

[frank.lukas]

It is very questionable whether such mods are really necessary, I don't think so! It is a shame that people often break Atari hardware with do such mods. You shouldn't do something like that without the right tools and experience.