DRAM isolation for 4MB MMU type upgrade question

[eightbit]

I figured I would post this in the "noob" section, as technically that is exactly what I am (at least to the Atari ST and RAM upgrades)

I recently (today) purchased the upgrade and am scouring the forums and the net to help better educate myself for the installation when it arrives and I have what is probably to most a dumb question...so please bear with me

The machine I will be installing this into will be a 520STfm NTSC model. I realize I have to disable the onboard DRAM to install this which is not a problem. I have the basic soldering skills to perform this task at least

I have watched now two videos on youtube (one is GadgetUK and another from someone who I cannot recall at the moment). Both had 512MB machines and in both videos they had only lifted R60 and R61 and wired them to 5V. However, the documentation here shows R59, R60 and R61 lifted and wired to 5V.

I am tending to lean on the documentation from the developer of course over videos, but why would these people only have the CAS lines lifted? And, why would that work when R59 is certainly involved with the lower bank DRAM on these 512K machines?


Again, sorry for the noob question....and sorry if this has already been answered somewhere. I just could not find an answer to this specifically..

Thank you!

[exxos]

Can't say about videos and what they are doing. But you should keep to the official docs for fitting. There are posts in the hardware ram section all asking about the resistors. Really depends what revision board you have.

[eightbit]

Can't say about videos and what they are doing. But you should keep to the official docs for fitting. There are posts in the hardware ram section all asking about the resistors. Really depends what revision board you have.

Agreed. Thank you. I will stick to the official documentation. I was just curious as to why they would not lift that resistor seeing that the docs clearly show that it is something that should be done to test the new installation. Who knows...

[exxos]

They probably used some other ram expansion as a reference . Technically you may only need to lift 2. But I try to keep things simple and not get involved with resistor numbers as they could be different numbers across various boards. R60 on some boards may not even be in the RAM circuit on some revisions.

So what I do is quote lifting all the 68R resistors. Even if they have the same numbers and still part of the RAM circuit, you can't assume they have the same signals running through them.

So lift R60 ? Or what ever resistors, may be correct for the particular board in the video or whatever, or they may have found information elsewhere and incorrectly lifted the wrong resistors. Even if they show it working, I've seen people basically shorting out the ram and killing stuff.

Same old problem of the internet and information. I really would avoid any information outside of this forum, unless its on my site hosted on exxoshost server. Sadly too much nonsense out there, which was one of my motivations of creating this forum to break away from it all.

Because there are so many revisions of boards, it would be pretty hard going to cover and document every board and resistor numbers. It would just end up confusing people. There are common things on similar looking boards, such as 68R resistors next to the MMU, so I try to illustrate those locations rather than resistor numbers. The boards may look identical but have different resistor numbers. So resistor numbers are almost meaningless.

Of course if in doubt, people only need to open up a post here. I know the resistors on the STM confuse people. I think there is only 2 to lift on there. But if people ask, and send me images once the job is done, i can update my site with that revision of motherboard.

[eightbit]

Thanks for the response exxos. All of this makes perfect sense. I will say the documentation that you have online now regarding the installation is excellent. High quality large images with very good up close shots in a clear step by step format. I will follow it to the tee

Refreshing to see that since I have worked with some projects with really poor documentation that was nothing like this at all.

Good stuff. Can't wait to give this a go!