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AuthorTopic: A2000 (B2000) tower assembly (U540 / U541)  (Read 973 times)

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Offline thomasM74

A2000 (B2000) tower assembly (U540 / U541)
« on: May 18, 2021, 12:27:28 PM »
Hello All

I would like to ask for guidance about a certain piece of hardware that came soldered onto a rev.6 A2000 motherboard.
Initially I was convinced this is what used to be called a "Buster tower" assembly (to fix the rev.1 Buster chip flaws) but now I am not so sure anymore.
This assembly is also included in the A2000 schematics.

The point, why it bothers me so much to find out what that thing does is because I am re-building the A2000 on a new PCB (Floppies209 rev.1.8.5 PCB) and don't know if I should (or not) install this assembly on the new motherboard.

Any advice is greatly appreciated.


Offline Castellen

Re: A2000 (B2000) tower assembly (U540 / U541)
« Reply #1 on: May 18, 2021, 09:12:11 PM »
That's also known as the "Tokuda Tower", which was a modification to allow use of a certain type of DRAM.  I can't tell from your photo, but presumably they're LH64258 or similar other static column DRAMs.

You don't need that tower board fitted if you instead use TC514256 256kx4 DRAMs (or equivalent) that are more commonly used in the rev 6 A2000, and rev 6 and 8 A500s, etc.

Offline thomasM74

Re: A2000 (B2000) tower assembly (U540 / U541)
« Reply #2 on: May 19, 2021, 07:20:57 AM »
Thank you for info.

That makes totally sense and after desoldering indeed, "tokuda" is written on it.
Just for reference whomever reads this post in future: my A(B)2000 Rev.6 motherboard which came with tokuda tower soldered on has LH64258 (120ns, SHARP) memory chips. According to some datasheet they are "static" type hence the need for the "tokuda tower" fix.

Now it is clear, since I plan to use regular fastpage dram chips on my new A2000 build, I just install the regular U540 and U541 chips according to schematics and ignore the tower build.