🚀 go-pugleaf

In article <8609021508.AA25295@mitre-bedford.ARPA> jhs@MITRE-BEDFORD.ARPA writes:
>Your fix sounds eminently reasonable to me.  The choke might be for RFI and
>spike protection.  Finding a better choke (same inductance, lower series R)
>might be still better, as shunting the existing choke will reduce the
>inductance as well as the series resistance.  The only penalty then may be
>the cost of the choke, which is probably not a problem if viewed as part of
>the cost of the upgrade.  Shucks, even buying a heftier power supply would be
>a cheap way to get a 1MB ST, starting from the current $495 price of the 520!
>

I have had the same symptoms after upgrading my 520 to 1Meg and,
hearing (reading) the chatter about problems and weaknesses with the
original power supply, was ready to swap it for a new switiching power
supply or something.  Recently, though, I talked to a hardware hacker
type in the East Bay (east San Francisco Bay, that is) who told me
that the original power supply, bad though it is, is not where the
problem lies.  He has done (and repaired) many ST upgrades and his
procedure includes changing an inductor on the right side of the ST
board (with the RAM at the bottom or toward you).  The original coil
is rated at about 4.something micro-henries.  He replaces that with
one of 2.2 micro-henries or less.  His claim is that this will prevent
the power drop to the RAM that is causing the problems.  He also adds
an additional buffer chip.  I am unwilling to post what I remember
of his instructions since I am not a hardware engineer or very knowlegeable
of such things and I would mislike being the proximate cause of someone
frying their ST.  If there is any interest from the net in complete
instructions, I will try to get him to write them up and I will post
them.  I would also be interested in comments from other hardware
people about this approach.

Sweeney
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