FE5680A Rubidium Standard: No Output and Not Locking - Page 1
Forum section: electronics / repair

author: ZGoode
author_rank: Frequent Contributor
timestamp: September 22, 2024, 09:07:36 pm
content: I just received a used FE5680A that I got from eBay which I suspect is dead. While I await a response from the seller I was wondering if anyone had suggestions on things to check with the unit, since if it is an easy(ish) repair I would like to attempt it. I paid nearly half of what I have seen other units go for on eBay so if it is a relatively easy fix I would like to try and revive it. One thing that worries me now, that I did not think about when I bought it is that the sticker covering the screw was broken, which means someone has probably opened this unit before I got it.I followed the pinout found here on Gepettos blog,https://www.geppettoelectronics.com/2015/09/fe-5680a-breakout-board-users-guide.html,since my unit appears to match his. The +15V current draw starts at around 1.80A and goes down to around 700mA/800mA after warming up, so that appears to be following the correct values so far. I see absolutely nothing on the RF output using my scope or counter, and the LED never turns off to indicate a lock. When connecting the +5V line to a separate PSU there is 0mA current draw which makes me think some kind of fuse or something is blown. Is there anything that I should be checking to see if this unit is salvageable?

author: hgl
author_rank: Regular Contributor
timestamp: September 23, 2024, 09:26:49 am
content: Look here for more infohttps://www.ka7oei.com/10_MHz_Rubidium_FE-5680A.html

author: ZGoode
author_rank: Frequent Contributor
timestamp: September 23, 2024, 03:44:51 pm
content: It looks like I have the same version as the person that posted on this thread:https://www.eevblog.com/forum/chat/identification-of-my-latest-ebay-purchase/Unfortunately, there is nothing on that post showing whether or not he got it working. Assuming mine is the same as his, it looks to be one of the very old revisions and might be EOL or not even work anymore.There is a blinking LED on one of the top boards when I applied 15V and removed the top shell. Nothing appears burnt or exploded, although it does have a very "toasty" smell to it (not burnt, more like hot dust or burnt dust due to the heat of the oven). Mine does have the SP233 RS232 transceiver on it, so I was thinking maybe if there is some way to talk to it to see if it is still alive? Is there any way to do this in Windows with an RS232 adapter? I don't want to have to go dig out the old DOS computer for this if I can avoid that.Edit: My main goal here is to see if this is relatively easily salvageable, because if it is not I am going to just return it to the seller who listed it as used, (he said probably working but does not have equipment to test)

author: ZGoode
author_rank: Frequent Contributor
timestamp: September 25, 2024, 04:12:17 am
content: I measured an internal test point according to the document I found here (on page 3), and it measured 8.39109MHz without locking. While being out of tolerance, the sine wave appears to be very clean and noise free from just looking at it on my scope (will hook it up to the spectrum analyzer later when my coworker is done using it). That is extremely out of tolerance, but I have no clue as to what that could be from. Another thing I noticed is that even though it has all the parts that would take 5V, the pin on the DE-9connector which is supposed to take 5V does not actually draw any current at 5V. This could explain why I am not getting an output on the DE-9, but not why the frequency way out of tolerance.

author: 807
author_rank: Frequent Contributor
timestamp: September 25, 2024, 01:36:26 pm
content: Quote from: ZGoode on September 22, 2024, 09:07:36 pmThe link points to a page that doesn't exist because of a comma at the end. Here's the working link:-https://www.geppettoelectronics.com/2015/09/fe-5680a-breakout-board-users-guide.html