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

[WB6BNQ]

Hello Ulf,

It may be the SAT orbital table is quite old and it will take quite a 
few SAT passes before the new table can be rebuilt.  Also, regarding the 
OCXO, it also may not be working and as it warms up and approaches a 
near on frequency point it will appear to be locking on until the system 
see it is not and alarms the operator.

I would give it a week of on time before doing anything rash.

good luck,

Bill    WB6BNQ


On 6/13/2023 1:36 AM, Ulf Kylenfall via time-nuts wrote:
> Regarding the Pendulum (Rapco) 2804B from a flea market...
>
> I spend some time trying to fix it after downloading the manual
> kindly provided by Lisa Perdue.
>
> First, I resoldered the main PCB as I could clearly see a number
> of poorly soldered thru-hole components. This solved an initial problem
> where the display and LED-panel randomly got black. (Not the
> units screen saver.)
>
> Scrolling down the pages and trying different settings for the OSC2
> ("OSC" - Depending on various options), in this unit a 10MHz unit
> with a de-facto standard footprint) I recognized that the locking procedure
> seems to be pretty static. No "adaptive" algorithm whatsoever.
> Two settings available, short and long for re-synchronization, the
> short being some 8 minutes (Default).
>
> After having placed the antenna outdoors and the unit sees a large number
> of satellites, it starts acquiring a lock, a procedure that takes several
> hours during which thew OCXO control voltage slowly adjusts the control
> voltage.
>
> When at last the unit stabilizes, the OCXO is about +0.5 Hz wrong.
> What then happens is that the unit seems to realize that something
> is wrong. The two LED's "GPS" and "CONTROL" goes out. An alarm is set
> and this situation persists for a few minutes after which the operation
> returns to normal. The Control voltage (low resolution) seems
> to be unchanged.
>
> In one of the test menu pages "LOOP Page", a parameter "Control Index" is listed.
> My unit reaches 2, a number not listed in the manual. It should be between
> 4 and 8.
>
> At the same time, the number of satellites remains high and with
> fine S/N values.
>
> The manual was of great help in using the menus but the lack of
> service documentation (CLIP) makes further troubleshooting difficult.
>
> Right now, I am inclined to beleive that the problem could be the
> OCXO that is malfunctioning, being unstable. It also gets a bit to hot
> compared to what I have felt from other similar units.
> Having a few compatibles, I will try to replace itand see if there is any improvement.
> Ulf KylenfallSM6GXV
>
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