LisaList2

There are two safety interlock switches in the Lisa, one at the top of the rear of the Power Supply, and one on the front at the lower left of the CRT.

These are wired so that the PSU will not start up (or will shut off) if either of the front and rear panels is not fully installed; no doubt due to the expensive lesson learned from Apple ][ users sometimes inserting/removing expansion cards with the power on.

When troubleshooting, it is often useful to defeat these interlock switches (eg. by jamming in a folded piece of paper to trigger them), but for a non-technical user or a more 'original' unit, having working interlock switches can be desirable.

For a few decades, the particular styles of interlock switch used in the Lisa was not normally stocked by distributors and difficult to obtain, but currently (June 2024) substitutes are readily available at about US$ 2 each.

The following parts may be useful if you wish to replace a broken interlock switch:

PSU (all types) interlock switch:
  CIT SM3CQF0804L04
  DigiKey 2449-SM3CQF0804L04-ND
  This part has a long lever, and "Right" oriented right-angle PCB leads
  "F080" in the part number denotes a force rating of 80g, other force ratings are likely just as suitable if this part is not available.

Front panel interlock switch:
  Omron SS-3FL11P-3
  DigiKey Z6376-ND
  This part has a long lever, and solder terminals

  The similar SS-3FL11P-3T has quick connect terminals, which are too large to fit easily, but could be cut down if it is the only part available.

These sub-miniature "microswitch" replacements have long lever springs. The CIT version has a longer lever (which makes it less likely to jam in the opening of the PSU enclosure breaking or disabling the switch), but is too long for the front panel switch holder, so the Omron version is more appropriate for that purpose.

Edit: fixed typo