Durabrand PSTB1 digibox power supply repair


In my opinion there should be no such thing as cheap electrical goods. Manufacturers should be forced to sell products that are built to certain standards using quality components with a guaranteed useful operating life of at least five years and consumers should be made to pay higher prices for electrical goods so that they're valued more. As it stands though, an item such as this faulty Digibox is really sold as 'disposable'. It cost less than thirty quid eighteen months ago and despite seeing little use over the last six months its power supply popped last weekend.

Most people would sling the thing and pick up another cheap replacement from the supermarket as alternative models are now sold at around twenty pounds and probably also have a lifespan of less than two years.

Anyway, I've learned my lesson and I'm paying extra for the branded goods with the higher build quality from now on. In the meantime, I have no intention of chucking this unit away when it can be brought back to life with fifteen minutes effort at a cost of just £1.18 including VAT for the actual components used. That said, playing with power supplies isn't much fun and you shouldn't attempt a repair unless you're confident that you know what you're doing.

This Digibox is a Durabrand PSTB1 and is somewhat ironically named as it hasn't proved to be a duarable brand for me. As cheap digiboxes go though, this one wasn't a bad little chap when it was working so I was keen to get the screwdrivers out on it to find out what had gone wrong.

Durabrand1

 
Upon opening the unit, it was fairly obvious that capacitor C668 had failed. This electrolytic cap had overheated and its plastic casing was shrivelled. The outer enclosure immediately above it and the PCB below it were showing signs of some high temperature marking. A quick scan of the internet soon found other people with the same sort of problems with the general consensus being that C667 and/or C668 (both identical caps) can fail, frying some of their neighbouring components as they do so.

In my case, I replaced C667, C668 and IC601 to bring my unit back to life. Enough waffling though, lets look at some snaps...

1. If you have the same symptoms as me (no power), check the fuse in the plug (if fitted)  and disconnect from the mains before disassembling. To get into the thing, flip it over, remove the rubber pads and undo the four screws.

Durabrand2

 

2. With the screws removed, flip the unit back over and lift off the upper enclosure.

Durabrand3

 

3. Unplug the front panel PCB connector (arrowed red). To lift out the main PCB bend back the tabs (arrowed green) and ease out the board.

Durabrand4

 

4. This is the area of the board we're interested in. Some or all of these components are the common failure points. The T3.15A fuse (A) labelled F600 on the board can be checked easily enough with a continuity or resistance meter. The four diodes (B) labelled as D614 to D617 can be checked with a diode tester or resistance meter. The IC (C) is labelled as IC601 and is a TNY265PN off line switcher. The problematic capacitors (D) are labelled as C667 and C668. This picture was taken after I had replaced the caps which is why they look okay. The replacements are rated the same as the originals (4.7uF at 400V) but are rated to 105C instead of the 85C originals.

Durabrand5

 

5. Upon replacing both my capacitors (even though only one had actually failed), I found I still had no power and IC601 was called into question as my failed cap had connected directly to it. I couldn't find a replacement TNY265PN but Farnell sell the higher rated TNY266PN at under a quid. I removed IC601 and fitted a DIL socket in it's place then inserted my replacement IC into it. The DIL socket was used so that if this happens again I can replace IC601 without having to reach for the soldering iron. The fitted replacement is arrowed in the picture below.

Durabrand6

With these three components replaced, my digibox was brought back from the dead and as the replacement components are of a higher tolerance, hopefully it will stay that way!

For anyone undertaking the same repair, parts are available from http://uk.farnell.com and at the time of writing, the capacitors had the order code 969-3343 (min qty 5) at £0.37 ex VAT, while the IC had an order code of 992-1346 at £0.86 ex VAT. Farnell do sell to the public and they dispatch orders the same day for free if you spend over £20 ex VAT.

Back to channel hopping now then - see if I can pick up something interesting to watch on this thing....