Polaris RAM IC TypesBy Gregory Ryan Freer 
You may find this information especially useful if you're having problems with your existing RAM: such as memory drop outs due to bad ICs, electrostatic damage, etc. Likewise, collectors—such as I—who wish to complete their Rhodes Chroma & Chroma Polaris setups with every possible accessory; might also find this valuable.
First off, there are eight removable RAM ICs inside the Polaris—each seated in sockets labeled Z2 through Z9—which gives you the ability to expand the onboard sequencer memory by installing optional expansion kits. The expansion kits were specific only to increasing the sequencer's ability to record longer songs and more of them. So those of us who had also hoped to increase the patch storage capacity, polyphony, or anything else were just going to have to deal with the fact that we were SOL; at least in that arena. Of course by today's standards, this single-track linear sequencer provides only a narrow range of basic functions; and would likely be considered much too primitive to many who might fail to see its other hidden side—which is actually quite nifty! Few modern synthesizers feature the old analog "Sync In/Out" interface; and even fewer provide the additional ability to convert digital MIDI clock signals to analog sync pulses—and vice-versa. The Chroma Polaris can do this; and it's a valuable asset if you're looking to control Pre-MIDI instruments or other devices with modern sequencers.
Fender released at least two kits: "Package-1" which contained four 8-Kilobyte ICs, and "Package-2" which contained only two 8-Kilobyte ICs for half the price. Initially, a Chroma Polaris has only 16K of RAM installed from the factory; but it can be increased to 32K, 48K, or 64K maximum. This is done by removing all eight of the original 2K chips—as outlined on the Memory Expansion Kit instructions sheet below—and installing four, six, or eight of the 8K chips provided in the expansion packs.
Although the original Fender expansion kits are no longer made, you may still be able to obtain the same type of ICs at certain used computer parts and electronics stores. In 1995, I installed Package-1 into my Polaris along with four other ICs that I had to buy at a place in Dallas, Texas known as Tanner Electronics. Since Fender had stopped making the Polaris nearly a decade before that, I was unable—at the time—to locate another Package-1 expansion kit. However, the additional four ICs that I did find have been working flawlessly in conjunction with the others to this date; despite the fact that they are slightly faster. The 8K ICs in Package-1 run about 15ns, whereas the 8K ICs that I later purchased run at about 10ns.
The instructions define the 2K ICs as the "6116, 2K x 8 RAM chips," and the 8K ICs as the "6264, 8K x 8 RAM chips." This alone may not include all the necessary details in order to find matching or compatible ICs; so I've listed what is actually printed on the 2K and 8K ICs below.
- 2-Kilobyte RAM Chips: HM6116LP-4
- 8-Kilobyte RAM Chips: HYUNDAI HY6264LP-10 (This is the compatible 8K type that I later purchased from Tanner Electronics.)
Paul DeRocco writes on the Polaris mailing list, "Hitachi HM6264A chips are what were actually used, but there are probably other manufacturers with similar part numbers. They need to have a standard 28-pin JEDEC pinout, 5V supply, data retention down to 2V, standby current of a few microamps, 150ns access time or faster." [August 2009]
For installation instructions, see Expanding RAM in the Service Manual.