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Joined: Wed Jan 01, 2014 1:36 pm
Posts: 61
Location: Toronto
Post 4771
I have just acquired a 4771 regulated p/s.

I was suprised that it is'nt capable of producing 18 volts. Is this a problem? (I'm guessing its not)

should I add an additional transformer that will produce 18 volts?

what is the lowest voltage that will work on the "18 volt" output?
I'm thinking of puting in a 7815 or an LM317 to regulate it.

Fri Apr 24, 2015 9:25 am
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Joined: Sun Nov 09, 2008 2:49 pm
Posts: 733
Post Re: 4771
Take a close look at the solder for the "flea clip" terminal solder joint to see that the end of this is extending through the solder joint for it on the bottom side of the board. If the joint is a smooth, shallow dome of solder, it is likely the terminal was not pushed through the board enough for a reliable joint to have been made and a desolder/resolder is needed. With the solder removed, use force the terminal down into the hole so there is at least a couple of mm of the end through the hole and above the plane of the pcb solder pad and re-solder. Otherwise, there could be an interruption in the printed circuit board copper and a likely spot is break at the solder pad for the terminal. Gently scrape the adjoining copper with a knife edge to expose shiny copper and flow some solder to this area. Form a piece of small bare wire to the shape oaf an eyelet to fit the pad with a stem to bridge the break. Tin/flow solder to this piece and solder it to the pad with the stem bridging the break. If the pad/trace interface is not broken, it might be a nick or scrape of the trace leading to the pad. Follow it back from the pad looking for a scratch or break/gap and repair this by scraping to expose shiny copper and flowing solder with a wire piece as a reinforcing bridge. Sometimes a green to black area occurs on a spot where something corrosive got on the copper and ate though it resulting in a need for a wire bridge repair spot.

The modules in a 4700/2720 series modular which use the 18V supply and are affected by possible excess ripple (when the loading on the 18V supply is great (many modules connected to this voltage supply), the simplest approach is to substitute resistor and capacitor power supply filtering components on the module in question, ie 1000uF capacitor on the 4710, 1000ohms on the 2720-5/4750.

4771schematic.jpg [ 102.19 KiB | Viewed 8236 times ]

Scott Lee

Sat Apr 25, 2015 2:04 am
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