The GPS at 200m has quit reporting. I noticed 200m was an outlier in the "chronyc sourcestats" output on flux. This listing shows an offset of 1051 microseconds for 200m instead of +-4 microseconds as the others:
chronyc sourcestats 210 Number of sources = 6 Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev ============================================================================== 50m 39 21 10h -0.000 0.001 -2198ns 13us 100m 5 4 68m +0.002 0.124 +4085ns 27us 150m 32 15 534m +0.000 0.001 +2403ns 11us 200m 7 4 103m +0.058 0.024 +1051us 16us 250m 43 21 12h +0.000 0.001 +1879ns 12us 300m 5 3 68m -0.001 0.145 -1918ns 31us
The serial port doesn't show large values of fe (framing errors) or breaks:
root@200m root# cktty 3 3: uart:XR16850 mmio:0x10000000 irq:122 tx:1936 rx:808452280 fe:24 RTS|DTR
I don't think power to serial port 3 can be controlled with "tio 3 1/0". When I tried to power off the GPS on 150m, the output to "rs G" did not stop.
As a workaround, I edited /etc/ntp.conf on 200m and added 150m as a server. So there is no urgency to replace this GPS.