[time-nuts] FE-5680A word of caution Thursday, April 7, 2011 10:20 AM From: "Jerry" Add sender to Contacts To: time-nuts@febo.com Just a word of caution to possible buyers of the Chinese Rubidium FE-5680A boxes. There has been a lot a discussion on the list lately about using the popular FE-5680A as a portable frequency standard and I have being working on using one of the cheap FE-5680A boxes myself. I have found that many of them do not output a useful 10 MHz signal. The 10 MHz output is not close to the expected frequency tolerance. The first of the units that I received puts out a signal at 9,999,945 Hz. The vendor then sent a second unit which puts out a signal at 10,000,025 Hz. The vendor is in China and while he has been willing to work with me by sending a second unit with me paying only postage, the time delay in shipping from China and the cost of postage is prohibitive. What concerns me the most is that the vendor says that both units were tested before shipping. In reviewing the Internet I found several other reports of similar problems with FE-5680A units. The units that I have been working with are FEI FE-5680AFEI P/N 217400-30352-1. These units all require a 5 volt input in addition to the 15 to 18 vdc input and these units are not programmable via an RS-232 port. These units are being advertised by several vendors on E-bay. I am sure that there are good FEI units available but there is no way of telling which are good and which are bad until you get the unit and check it out and if it is bad you may just be stuck with it, Only my experience yours, may be different Jerry Here's what I worked out for the pins on the DB-9 on my5680A... 1 +15V near 2A initially, dropping to about .8A warm 2 gnd 3 lock high = unlock 4 +5V about 160 mA 5 gnd 6 1 pps out 7 10 MHz out 8 RS-232 Rx (into rubidium) 9 RS-232 Tx (from rubidium) The initial impression from the seller was that only 15V was needed. The info on the FEI pages don't mention needing 5V in any option. A lot of the pin functions are different from any description I have seen. I think I have the same full board you have. I looked at it back around the beginning of the year. If I remember right, the RS-232 pins of the rubidium get fed from off-board signals. I did power it up using this board once. There is a dual color led at the edge of the board that indicates lock state, if I remember right. Does your board have a sticker on it somewhere that says: SGLA4000B High Stability Osc Assembly? After lots if web searching, I figured that this seems to be part of older Motorola Cell equipment. I found a site that says they repair them. I tried sending an email asking if they have any documentation, but got no reply. Maybe later I can find time to scan the board. What I remember from the hacking I did, was that there didn't seem to be anything intelligent going on on the board. I don't remember any details though, maybe I missed something. Oh, on the side of the rubidium there is an adjustment screw. I thought for sure this would adjust the C-field and hence the freq, but I don't see any result by turning this. No idea what it is for. I tried all sorts of things sent to the serial port but never saw any effect or reply. I tried this at various baud rates. I also scoped the other side of the MAX3232 chip inside, so I know the data was getting in there. The other port of the MAX3232 is connected too. It goes to what must be a maintenance header inside. Nothing interesting came from trying that port too. So, if you feed it both 5V and 15V, I'd bet your unit will come up and give you 1 pps and 10 MHz. If, like mine, the frequency is a little bit off, it sure would be nice to know how to adjust it. -Rex, KK6MK