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Old 25th May 2016, 4:59 pm   #4
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Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 3,887
Default Re: Roband Varex 60-5 power supply

Thanks Dave, that's certainly a thought. Having got quite a good selection of power supplies (admittedly not a stabilised one with exactly the voltage and current rage of this exact one) I'm not going to spend a lot of time on it.

Like a number of pieces of test gear at this sale, it had a 'strange' two pin plug connected, but with a side earth connection. There was some debate in the room as to whether these were for American 110 volt mains. I thought this very unlikely and the 'different' plug was probably so that they would only be used on a 'dedicated' (probably isolated or otherwise protected) workshop supply - I have to admit that I kept quiet as this was likely to put other folk off items that I may be after After all, these were all apparent 'radio hams' (not that that would necessarily mean that they would be particularly knowledgeable about such things), anyway, at an auction it's every man for himself. Having said that, I did call out "let him have it" on a number of items when I felt that the person bidding against me was perhaps in more need than me (and also because I'm a bit 'tight' and also trying not to buy too much old junk to take home).

Today I had a look inside the power unit - it's been opened before as there's a washer missing from one of the case screws and another only finger tight. I think the voltage pots have been out and dismantled before as
the 'orientation' of them was different to the current ones, causing stress on the wiring to the green LED, dislodging it from its holder, so there's been a history of trouble in this area. I note that it was mentioned in the thread that I linked to about the fact that the 'fine' voltage control wasn't working, so linking this pot out could have been what was done on that power unit.

The pictures below show the unit 'as-is' and with the pots removed from the front panel - the values are different from those shown in the circuit, so suspect there'll be some other production differences if one were to look closely. Having now moved the red/green wire onto another terminal on the coarse pot the unit works perfectly with no sudden doubling of voltages. It has to be said that there's something to be said for the 'bog standard' un-regulated power supply with just a transformer, rectifier and smoothing capacitor when it comes to the risk of component failure causing catastrophic increase in voltage in these complex regulated supplies. I would think that this power unit would have been very expensive in its day.

Pictures below of the innards of the unit - once it stops raining and dries up outside and before I put the case back on, I'll take it out and give it a blow out with the air blower and fine paint brush to remove all the years of muck, dust and the large dead spider that I noticed behind the rear heat sink.
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Last edited by Techman; 25th May 2016 at 5:17 pm.
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