samedi 4 juillet 2015

How to upgrade the programm memory of the prophet VS...

Like many devices of the late 80s, the parameters memory was often backuped by an internal battery. It is the case of the Prophet VS synthesizer. The 'patch memory', plus some of the internal parameters site in a couple of a static ram electricaly backuped by a lithium battery.

But after many years, the capacity of the battery become insufficient to ensure a proper backup of the SRAM when the Prophet VS is powered off. Worse, when the lithium battery is very 'out of date', it is possible to observe a leak of acid liquid witch spreads off the circuit board. It could be really catastrophic for the printed board.

So, since a few month, I create nonvolatile memory replacement for the standard SRAM in 2, 8, 16 or 32 Kbytes.
I decided to create a special edition for the Prohet VS. Special because I had to respect a protection against the potentially corruption of the data by writing wrong values at wrong addresses at the power on of the synthesizer. I had to create a special circuit board for that and replace the original SRAM with the new nonvolatile SRAM.

First, the main board of the prophet VS :


A very classical 68000 board!
As you can see, there are the two backuped SRAMs between the two ROMs. The first operation was to remove them :

Without SRAMs and without the battery.
Then, I also remove the internal battery. The next step was to place two supports for the new nonvolatile SRAM, then to put them into the supports like this :

A main board up to date !
As you can see, not only the two nonvolatile SRAM are in place, but the battery space in now empty. Furthermore, you can observe tiny connectors on the two nonvolatile SRAM.
No! You don't dream, this connectors will allow you to select ONE of the FOUR bank now availables!!!
Yes, it is possible because the original SRAM are 8 Kbytes capacity, but the new one have a 32 Kbytes capacity.

And the result :

One more improvement!

  • No more battery.
  • 400 programm capacity, into nonvolatile SRAM.
  • Two ELD5530, my CEM5530 replacement.

If it continues I will rebuild this Prophet VS by myself !!!

And, does it work? Yes, of course!

I have to reload my patches into one of the four ram bank, and to find a solution to select the four banks now availables. I don't have decided yet how to do that. I want to conserve the original look of my VS, so perhaps a kind of 'programmer' like the PG200 of the JX3P...




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