Game-Tech.US

LED change:

Super easy mod, can install any color you like, or a color changing LED, like this one.

$5 for single color LED.
$7 for color changing LED.

SFC mod:

Another easy mod, removing the tabs inside the throat of the cart slot will allow a US SNES to play Japanese (Super Famicom) carts.
$10

Lockout mod:

This will allow you to make your US system region free.
A switch is used to re-enable the lockout chip to be sure all US games still function properly.
SFC mod also performed since JP carts have different case.
$25

Svideo:

The SNES is already s-video capable with the right cord, find them on ebay for as cheap as $5.

Repairs:

Please note I do not do any other repair work to the snes, only what’s show below.

Fuse:
If you system won’t power on and you’re sure the a/c adapter is good then the internal fuse is most likely blown, easy fix.
$5.

Power Jack:
A notorious issue is the power connector breaking.
I haven’t found a snes style replacement jack only, but you can find new entire rear panels.
Nesrepairshop.com had whole new plates available, but are out of stock.
I think there may some for sale on ebay too.
These will prolly eventually break as shown below if the plug is ever moved around.
However, the repair jacks shown in the 2nd and 3rd pics are unlikely to ever fail.
Installation of a jack that accepts the more common plug (5.5mm x 2.1mm) is $15.

Retr0Bright:

The SNES is also notorious for turning yellow, it looks awful, but it can be returned to its natural grey color with the Retr0Bright process!
This process is best done with a lot of strong sun light so I would only attempt this May through September.
I do not offer this service!
I only added it here because I know it works, but also know its really time consuming and a really gratifying DIY project!