Remaining semaphore signal boxes

[RichardAsh1981]

Yes. An increasingly niche capability along with the maintenance teams. Even back in the 1990s Exeter was maintaining Greenford’s (west London) interlocking.

Skills can be a problem, but at least a mechanical system can have more or less any spare manufactured by a reasonably basic workshop - if necessary by copying the broken part. Electronic interlocking spares can easily become literally unobtainable (without effectively designing a replacement system from scratch) if key semiconductors or modules become unavailable, or firmware data is not available.
One of many reasons why Birmingham New Street had to be re-signalled (to replace the 1960s PSB) ahead of lots of mechanical installations - it was fast becoming impossible to keep in service.

 

[MadMac]

Yes. An increasingly niche capability along with the maintenance teams. Even back in the 1990s Exeter was maintaining Greenford’s (west London) interlocking.

Also becoming rather “niche” is design expertise on the 1960s era “geographical“ interlockings.

 

[Ken H]

Also becoming rather “niche” is design expertise on the 1960s era “geographical“ interlockings.

This is the cause of the problem. Mechanical stuff can be made to work for ever with a little judicious maintenance
Relay and electronic stuff definitely dies as parts become unobtainable so needs replacing.
So maybe we are reaching a point where the renewals resources all are needed to replace old non mechanical equipment, and places left with mechanical signalling will be left as is.

 

[merry]

AIUI, there is very limited electronics in 60s / early 70s PSB installations, they are primarily relays, buttons, switches, lights and a whole lot of wiring.
It is the wire (insulation) and relays ( suffering metal migration into the insulation) that are life expired and not replaceable without very extensive (and expensive) work. But yes, that is ehy they are being upgraded first.

 

[Ken H]

AIUI, there is very limited electronics in 60s / early 70s PSB installations, they are primarily relays, buttons, switches, lights and a whole lot of wiring.
It is the wire (insulation) and relays ( suffering metal migration into the insulation) that are life expired and not replaceable without very extensive (and expensive) work. But yes, that is ehy they are being upgraded first.

When did panel processors come in? I think Cambridge was an early one.