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Old 19th Sep 2017, 2:26 pm   #1
MrBungle
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Default Quick Farnell E30/2 refurbishment + modifications

For the sake of documenting it, I spent the morning doing a quick refurbishment and modification on a Farnell E30/2 power supply. It was working perfectly before so this is more preventative.

Firstly it was stripped down, cleaned and a rather angry spider evicted.

The next step was to replace the RIFA and Philips electrolytic capacitors in the unit. The two Philips ones were showing relatively high ESR. They are on the main board and front terminals. The RIFA is between earth and minus voltage terminals and fortunately not across the mains! I added a 1N5401 diode across the output terminals to protect against reverse voltage. I also replaced the main 18v reference zener which was mounted too close to the board and had burned it. This is now 1cm off the board.

Finally the heatsink was removed from the rear and another 1N5401 installed across the collector/emitter terminals (after the resistors) to stop the driver transistor blowing up if there is a load dump while driving something. I tested this worked, which it did by connecting it to another power supply and turning this one off.

Works nicely and should last a few more years now

After (terminals):

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After (heatsink/transistors):

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Dead bodies:

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No picture of the board as it was rather unexciting.
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Old 19th Sep 2017, 3:14 pm   #2
mhennessy
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Default Re: Quick Farnell E30/2 refurbishment + modifications

Good job! Inexcusable of Farnell to have omitted those diodes originally, but easily retro-fitted. To make it simpler, the one across the pass transistors can be fitted to the underside of the PCB - I don't have a photograph of that on this computer, but the schematics I scanned and posted earlier (with the diodes added in pencil) show how it's electrically feasible to do: https://www.vintage-radio.net/forum/...80&postcount=5

If only these units had a variable current limit... I've often thought about modifying them. Up in the attic I have the remains from 2 of these that went wrong at work, and from all those bits I'll be able to make 1 decent unit - but as it's already a pile of bits, it's tempting to stick my own design in there. The metalwork on these is much nicer than the Thurlby PL320 units, and they are rather more compact.

I've had the output electrolytic explode on more than one occasion (we had dozens of these at work). Not sure why, as those Philips types are usually pretty reliable. I don't recall a RIFA letting go in one of these, but that's just a matter of time...
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Old 19th Sep 2017, 3:39 pm   #3
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Default Re: Quick Farnell E30/2 refurbishment + modifications

I looked at installing it on the PCB but decided I'd stick it across the transistors. The PCB is a relatively fragile one so I wanted to keep away from it as much as possible. Plus I used rather large 3A diodes!

I actually bought this because my PL310 has some display problems and it is so large so completely agree. Not too bothered about current limit. Plan is to replace my other PL dual with an LT30/2 which does have current limit.

I have had numerous problems with those Philips capacitors. Recently I had a whole scope taken down by one. Never seen one explode though. Decided to replace them with their distant descendent Vishay/BC equivalents.
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