[time-nuts] Re: Symmetricom S250 Freeze-Up

[Nick Whalen]

Wilko has a good suggestion, the power supplies in the S2xx/3xx series 
have a history of failing miserably.  While the supplies are definitely 
repairable (esp if you catch them before the caps fail), there's also a 
'new' option.  Specifically this unit: 
https://www.mouser.com/ProductDetail/490-VSBU-120-T515A.  You'd need to 
pull the existing supply board out of its enclosure and replace it with 
this one.

I swapped out the PSU in S350 last year with the above linked 
replacement and it's been working great ever since.  I think I had to 
tweak the DC wiring layout a bit, but that was about it. Should you go 
down this route, feel free to ping me and I can go dig up my pics :).


Next option: These units have a large thermal interface pad between the 
CPU 'heatsink' (basically just a big block of metal, probably aluminum?) 
and the top of the case.  If the unit has been opened a lot, or the pad 
is bad, you could have an over-heating CPU. One way to check this would 
be to open the top of the case when the unit is on and has 'hung', and 
check the temperature of the heatsink block. I'm not sure what proper 
idle temperature is right off the bat but that block really shouldn't be 
above 40-50C in normal environments.  That said, if you have a 
rubidium-optioned unit those throw off a _ton_ of heat, and that will 
exacerbate any thermal issues you may have.


I currently have a S200 (TCXO), S300 (Rb) and a S350 (Rb) in working 
order, so not exactly what you have, but I definitely can help with 
providing measurements of what  'normal' is, if you get to that point.


Nick


On 7/26/25 09:15, Wilko Bulte via time-nuts wrote:
> Bit of a blind guess: older unit, with over time degraded power supply? Typical failure scenario for (SM)PSU are electrolytic capacitors that have lost (part of) their electrolyte. Which means capacity of the capacitors goes down the drain.This can be temperature dependent, making the unit work while cold, fail once warm, work for a bit after being allowed to cool down for some time, etc.
>
> best,
>     Wilko
>
>> On 26 Jul 2025, at 17:15, Adam Zeloof via time-nuts <time-nuts at lists.febo.com> wrote:
>>
>> Hi all,
>>
>> I picked up a Symmetricom S250 NTP server last weekend, and I'm having some
>> trouble with it. When powered, it'll run for a couple of hours before
>> freezing up. The LEDs on the front all turn red, the screen stops, and the
>> web interface is unreachable. I've tried factory resetting, upgrading from
>> the originally-installed 1.26 Firmware to 1.36, and installing a new CF
>> card. If I reboot after a freeze, it usually freezes again within a few
>> minutes unless it's sat for a while. Any ideas or solutions would be
>> appreciated!
>>
>> Thank you,
>> Adam
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