View source for Support - Apple IIe

==Issue: One card works when installed. Multiple cards do not work.==
Likely Reason(s): Weak or defective 74LS245 (bus transceiver) or PSU.
*Replace the 74LS245 on the motherboard and retest.
*Fully rebuilt or replace the PSU.

If the LS245 fixes the issue then the bus transceiver is weak, likely due to ESD damage or was damaged by the PSU from spikes or other unknown issues. ESD damage is most likely as users over the years mishandled the cards and IIe motherboard. Static shocks don't out right destroy ICs in most cases. They weaken their gates (transistors). After a certain amount of damage the IC can no longer perform to its rated specs, and in the case of the LS245 this would likely be related to how much of a load (other ICs) it can drive (talk to). The more cards you add, the more load the IC needs to drive for example. With some luck the 74LS245 on your motherboard is socketed and can be easily replaced. ReActiveMicro would recommend DigiKey for ICs in case you don't have any spares on hand.

A PSU can likely damage ICs via failing parts, being allowed to fail when under load, or perhaps from transients (spikes) in your AC power. A good power strip (Panamax 360) and line filter (Tripp Lite LC1800) would be recommended, and should have their safety caps replaced every few years or when alerted to a failure. ReActiveMicro always recommends you fully rebuild or replace your PSU every 10 years, and never let it fail when in use.