[time-nuts] Rapco (Pendulum) 2804B - Troubleshooting . . . (II)

[Ulf Kylenfall]

Continuing the troubleshooting...

After replacing the OCXO, the frequency error is down to + 0.12 Hz
A stable, non jittering frequency offset. But of course - way out of spec.

The loop Index never increases above "4", according to the manual
indicating a low quality lock condition.

There is a setting "GAIN" (in the TEST-menu) that can be
set between 000 and 255. In the manual, this setting is 255 but
there is no explanation regarding recommended setting in the manual.

The unit suffers from frequent loss of GPS-data in spite of
a large number of satellites being seen with good S/N.
All of a sudden - the S/N drops to zero after which the GPS
LED goes out. If warmed up - the CONTROL LED also goes outand the alarm relay is activated.

This (or similar) behavior of the Trimble units was discussed in a Time-nuts
thread from 2016 with contributions from Skip Withrow et.al.

The GPS receiver module used in the Rapco unit is Trimble Resolution-T
52664-05. The Thread above mention that the firmware used, 1.16 in some
units can/should be upgraded to 1.17 using "Trimble GPS-Studio". 
This software, if needed is not available on Trimble home page as
of today, or it had been replaced.

That said, I cannot beleive that the receiver all of a sudden should stop
working unless there is either a hardware or firmware related issue
(such as flash memory rot/failure). Right now trying to find out
if there are drop-outs of the +5V supply, provided by an LT1074HV
switching sircuit. The +12V is supplied by another '1074.

Furthermore, I have also not been able to communicate using
the two serial ports where one of them is configured for
remote operation and the other for streamed timing data.
Ulf Kylenfall