Upgrading 32K -> 64K RAM

Hardware Hacking, Programming and Game Solutions/Cheats
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Rolo
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Joined: Sun Feb 10, 2013 7:36 pm

Upgrading 32K -> 64K RAM

Post by Rolo »

I successfully upgraded my Dragon 32 to 64 kBytes, as described in the very good article of R. W. Hall (1985) in the "publications/technical"-section of the Dragon Archive. :D
I just wanted to write down a short summary for people who may have the same plan.
That was kind of a brutal job, to cut of the patchboard of my issue 2-PCB and to desolder all those chips and components, which do not like to give up easily. Most of them have ugly bent wires on the solder-side of the PCB and stick to the pads. But in the end, I managed to remove the chips without cutting of the wires. I'm pretty confident, that the 16k-DRAMs survived the procedure. The PCB did, the lines and pads did not come off immediately.
That's what it looked like:
Original.JPG
Original.JPG (563.97 KiB) Viewed 1813 times
I decided not to use the patchboard any more, since I had to desolder the old DRAMs on the mainboard anyway - so way not use that space for the new chips? I ended up with:
NewDRAM.JPG
NewDRAM.JPG (868.98 KiB) Viewed 1813 times
Final job: changing the decoder a little bit, adding a few wires and cutting one line (red cross):
DecoderChanges.JPG
DecoderChanges.JPG (462.88 KiB) Viewed 1813 times
Before testing, the voltage jumpers (red circle, picture 2) had to be adjusted. Since I was lazy an hoped that the setting "d) Set the jumpers to l,4,5,8,l0", as mentioned in the article, would be ok, I did so and immediately fried two of the eight new DRAMS. :o When I sensed the smell, it already was to late. The fast chips burnt first and saved the slow ones. I only had one spare chip (of course) and therefore had to order a few new 64k-DRAMS. Fortunately they are cheap and still easy to get (ebay, electronic component sellers). The suitable 64k-chips all use single voltage supplies (5 VDC)(data sheet!). No more 12 VDC or -5 VDC. The correct setting of the jumpers is 1,4,6,8,10!
Now it's working and, for example, DUPLI-DISK2 recognizes a Dragon 64 and can therefore process bigger files, without overwriting it's own memory.
Finally: The Dragon-Dos Disk controller (LAFUMAT) is not affected by the changes of the decoder circuitry. Obviously it's only using IO-addresses of the top memory page.
All in all, the job took me about half a day.

By the way: Is there anybody out there, who is repairing Dragon 32s on a "regular basis" and needs a few spare parts (16K-DRAMS)?
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