When reviving an Acorn Archimedes there are some issues that are more likely to cause the computer not to come back to life straight away.
The lights may or may not flash on the keyboard and in all respects the machine appears lifeless. The power light may be lit.
This is quite a common problem and the most common cause is a faulty de-coupling capacitor. To be specific, the Tantalum 12V decoupling capacitor fails "short" and causes the machine to fail to power up correctly.
On the A300 and A400 series of machines, the capacitor in question is marked as C37 on the motherboard. It's rated at 100uF 16V.
In the A400/1 series of machines, the capacitor is marked as C53 on the motherboard. It is rated at 100uF 25V.
To test whether the capacitor is faulty, simply remove it and power on the Archimedes. If the machine powers up then you've found the problem and you need to replace the component to restore the machine to full function.
Given the job that this decoupling capacitor does, I'd recommend fitting a 100uF 25V capacitor to all of the models affected by this fault.
The A300, A400 and A400/1 series of machines are unlikely to be damaged by battery leakage as their batteries are remotely located away from the motherboard as pictured below.
If the AA batteries have leaked, remove them and thoroughly clean the contacts. You may need to re-solder the wires to the battery holder or in fact replace the battery holder completely as they can be eaten through by the alkali from the batteries.
The A540, A3000, A5000, A3010, A3020 and A4000 however all have rechargeable batteries in them which require servicing from time to time otherwise battery damage can occur as shown in the photo below of an A5000.
Take a look at some of the links below to see how battery damage can be addressed and for hints on battery maintenance.
Acorn RISC computer fault codes are reported via the flashing of the floppy drive light in a sequence of 8 blocks of 4 flashes. Each block of four flashes (e.g. long short short long) represents a set of fault and status bits which can be translated into a list of error codes.
Select the boxes that represent the long flashes from your computer to derive the fault code and its translation.