> From: d_thumim
>
> I am the owner of Chroma Polaris serial #01576, which has
> been sitting idle for many years now in my basement. It has
> gotten very little use and cosmetically it looks pristine,
> but of course with parts like these membrane switches you
> can't really tell if they work just by looking.
>
> I had not been aware that these machines had batteries
> inside, so of course the first thing I found when I opened it
> up was that the batteries (original equipment, apparently:
> they are Matsushita D cells labeled in Japanese) had leaked
> all over the battery compartment. I took them out and
> temporarily wired in a partly used 3V lithium cell from a
> camera - if I get the machine working, I'll fix up the
> battery compartment later. It still wouldn't boot up, so
> according to the instructions in the service manual I tried
> to adjust the resistors on the power supply. I don't have a
> scope, just a handheld tester, but I thought I'd try. First
> R17 until the LED came on, which allowed the machine to boot
> up but not make any sounds. Then R9 to adjust the voltage
> across P2-P3 - it started around 4.7, and with R9 turned all
> the way I couldn't get it above 4.85V. The spec is 5.00V +/-
> 0.01. Does that mean I need a new power supply? Is it
> possible to still get parts for these things? I'm willing to
> tinker a bit.

If it can't get up to 5V, it either means there's something worn out in the
supply, or that something elsewhere is pulling it down. My bet would be the
filter capacitors in the supply are dried out, and that the 5V rail has lots
of 120Hz ripple on it. If you had a scope, you'd be able to see this easily
enough, but you might also be able to to test this by hooking some
headphones across the 5V through a small capacitor (maybe 1uf to 10uf) to
block the DC. The rail should be quiet, but you'll hear a nasty hum if
there's ripple on it.

It might not be a bad idea just to replace all the large filter caps, even
if you have to hand-wire caps of a different physical form factor. They're
notorious for drying out. It's doubtful that any impossible-to-get part
(like the power transformer) is bad; the rest of the supply is just
garden-variety stuff you can get from places like DigiKey.

Since your memory contains nothing but garbage, you should also do the steps
on page 6-5 of the service manual. You may find this brings things back to
life--that is, if the membrane switches will let you.

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...