[time-nuts] Trimble GPSDO power suply unit

David Medin dtmspam at techemail.com
Thu Sep 11 15:05:20 EDT 2008


I'm glad to hear that Tom will replace the unit for you. I've worked with Asian multivoltage switching supplies for years, and what the manufacturer usually won't tell you is that their primary output (usually the +5) of a multivoltage PS needs at least a 10 - 20 percent (or so) minimum load in order for the whole unit to meet spec and be stable. I would never leave one of these operating unloaded for any length of time... The result is usually what you saw, or a secondary voltage that goes way out of spec and burns out the attached device or itself. I usually just tag an appropriate 5 watt cement resistor on this particular output just to be safe, even though I contribute 2 more watts to global warming.

This is not just an issue with Asian supplies, either. One of my favorite domestic supplies (from Red Rocket/EOS) has such a restraint, only they tell you about it explicitly in the specification. I have one of my EOS units going on my Tbolt, as I hear I will be a proud owner soon. The EOS units are whisper-quiet and are about the size of a RAZR cell phone.

-Dave

Date: Thu, 11 Sep 2008 06:06:34 -0400
From: ernieperes at aol.com
Subject: Re: [time-nuts] Trimble GPSDO  power suply unit.
To: time-nuts at febo.com
Message-ID: <8CAE20D3454F71A-844-24CE at FWM-M02.sysops.aol.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed


My Trimble GPSDO just arrive but I have a problem with the POWER Supply 
Unit.

After connecting all wires to the Trimble plug and made a check if all 
voltage is correct and left the PS unit to run
on the table without load/connecting to the GPSDO, about 15min got a 
big bang and the Power Supply Unit blow-up.
Opening the box found Q1 transistor / BUZ78 / blown and seems to me 
that it was a short around R1, R2 and C11
area, namely the two resistor had short to each-other...../ factory bad 
installation??? /
Anybody having a circuit diagram ????? I am trying to repair.....

Please help, I just do not want to throw the unit to the garbage can.



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