hugh@dgp.toronto.edu (D. Hugh Redelmeier) (12/09/89)
Recently 880139h [is that a first or last name?] at aucs asked what
he could do about his noisy 1040ST. I sent him this, but he
apparently doesn't know that netiquette requires him to post a
summary.
Anyway, I got the following from Atari Canada's BBS a few years
ago. It worked for me. Note: these are not guaranteed by Atari or
by me.
Hugh Redelmeier
{utcsri, yunexus, utzoo, hcr}!redvax!hugh
When all else fails: hugh@csri.toronto.edu
+1 416 482-8253
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Does your 1040 whine? When you boot up do you get the mosquito
repellent? If so, this is for you. It is the "official" Atari 1040
power supply fix for 1040's that have a high pitched whine emitting
from them. The problem is the switching power supply that is used for
the RS-232 port. It is supposed to switch at around 18 Khz, but due to
parts tolerances, it sometimes falls lower than that, the result being
a irritating "whine". It has falsely been decribed as "drive whine", and
defective power supply modules. The circuitry is actually on the
motherboard. This mod also cures a video "flutter" that sometimes occurs.
Faint horizontal bars float up and down the screen. If you are not faint
of heart, here are the instructions for the modification.
Note: I _do not_ recommend this if you are not familiar with electronics!
You will be playing with the power supply, and if done incorrectly, could
fry your ST! I am providing this info so that the folks that are out of
warranty can do it themselves. Also some dealers may not be familiar with
the problem (well, Dave Groves was also twisting my arm!).
I do not accept reponsibility for any permanent mushroom clouds that you
may cause, though I will be happy to help out if things go wrong (advice!).
Ok, here goes:
Take the case off of your 1040. Remove the power supply module. It's pretty
straightforward, as there is a plug for the wires. Untwist the grounding
tabs on the shield and lift the shield off of the PC board.
The parts to change are on the motherboard, below where the power
supply was, and to the right of the ROMS. Change:
Part no. From To
R17 1 ohm 5 ohms
L4 100 uh 220 uh
C28 100 pf 330 pf
Now, looking at the 1040 from the front, here is where the stuff is:
R17 is one ohm (brown - black - black), and is below C26 (yes,
that _is_ a capacitor!). L4 is the resistor looking thingy to the right
of the I.C., a TL497. It's color code is brown - black - brown. C28 is
located to the left of the I.C., next to a larger black capacitor. It's
color code is also brown - black - brown. While these locations should be
accurate, please note that they could, and may change at any time! It is
very important that you replace the correct components.
You will need a good soldering iron, and solder of course. A
desoldering bulb, pump or solder wick is also needed.
Parts should be +/- 5 % . Be sure and check the voltage at JP2 and JP3
(red and blue wires) for +/- 12 volts, +/- 15%. If not, it's time for the
service center!
The only part that is usually hard to find is the inductor L4. It is
available from Newark Electronics (they have branches all over the place!).
The part no. is 35F1885 and is called a Deci-Ductor. They cost around $4.00.
Well, that's about it. Hopefully after this point you will power up to
blissful silence (and saved some $$$ to boot!). Good luck!
Mark Sloatman 74206,356