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 <cjaysh...@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@febo.com
<mailto:time-nuts@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 wb4...@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
of the Amateur that holds the license"
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