[time-nuts] Symmetricom S200 PSU

Bryan _ bpl521 at outlook.com
Sun Oct 1 17:05:59 EDT 2017


Can second that, had a Tek 2465B scope with a faulty power supply. Only with the help of others more experienced in these repairs it was found to be a faulty opto-isolater that had degraded over time.


-=Bryan=-


________________________________
From: time-nuts <time-nuts-bounces at febo.com> on behalf of Glenn Little WB4UIV <glennmaillist at bellsouth.net>
Sent: October 1, 2017 11:23 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] Symmetricom S200 PSU

Opto-isolators degrade with time.
The "optically clear" material between the emitter and detector will
start turning opaque with time.
At least this is what my boss told me years ago.
We has a product that used opto-isolators to isolate our circuits from
phone lines.
After a few years of use, the boards started failing.
When we measured the transfer characteristics of the opto-isolators, we
found them to be degraded.
Replaced the opto-isolators and the boards functioned again.
Could have been a design error on our boards, who knows.

Opto-isolators ate cheap.

Replace it and see what happens.

Any and all parts are suspect, some more than others.
To me, it would be physically damaged parts, electrolytic capacitors,
opto-isolators, solid state devices then other parts.

73
Glenn



On 10/1/2017 12:26 PM, Lists via time-nuts wrote:
> Thanks for the reply Clint. I spent some time on it today with no luck, I do have some more info though…
>
> The primary seems ok, there is a steady 329volts DC across the big cap after the rectifier diodes.
>
> When you power it up under its normal load you can hear the transformer whistle, which you could not hear when it was working, also measuring the DC outputs gives almost exactly half the expected output, i.e.
>
> +2.54v
> +6.02v
> -5.88v
>
> Unfortunately I only have a multimeter and no ‘scope so any further fault finding is difficult. I guess the next step is to replace the mos fet that drives the transformer, or I guess it could be the feedback loop, which looks like an opto-isolator, doubt that the isolator itself would die, but there’s a PNP transistor driving it…
>
> If anyone has any other ideas I’m listening !
>
> Thanks,
> Chris
>
>
>> On 18 Sep 2017, at 20:21, Clint Jay <cjaysharp at gmail.com> wrote:
>>
>> Hi Chris, if it's not blowing fuses and you're sure you've got all the capacitors ( low value ones in the primary specifically) then check all the high value resistors on the primary and continuity from reservoir capacitor to switching transistor.
>>
>> The average SMPSU usually doesn't deviate wildly from the application notes of the switching controller so if there's no specific schematic that might be a lifeline.
>>
>>
>>
>> On 18 Sep 2017 20:08, "Lists via time-nuts" <time-nuts at febo.com <mailto:time-nuts at febo.com>> wrote:
>> Hello Fellow Time Nuts,
>>
>> Does anyone know where I can get either a circuit diagram or a replacement PSU for a symmetricon S200 NTP server?
>>
>> I’ve fixed the original one twice before by replacing all the electrolytic caps, this time it’s popped something more critical and refuses to come back to life.
>>
>> So I either need a new PSU or a circuit diagram so I can fault find on the original.
>>
>> I’m in the UK.
>>
>> Thanks,
>> Chris
>>
>>
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--
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Glenn Little ETCS(SS) USN Ret, ARRL Technical Specialist,  SBE ARRL TAPR
Amateur Callsign:  WB4UIV            wb4uiv at arrl.net    AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)  USSVI, FRA, NRA LM  QCWA  LM 28417
"It is not the class of license that the Amateur holds but the class
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