Openbox s10 power supply failure

istvan

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Greetings!

A few months ago I bought a used openbox S10 receiver on a local auction site for next to nothing + shipping. It worked fine for a while, with a few problems here and there (namely random reboots and the HDMI sometimes not outputting anything). Today I turned it on and - nothing. check the fuse and sure enough, it's blown. I removed the cable going to the main circuit (just to be safe) and replace the fuse, switch it back on, fuse blows again.

On closer inspection, the big capacitor on the HV side had some gunk under it so I decided to try my luck and replace it. I'm adequate enough with a soldering iron and I have enough replacement parts so it only took me 15 minutes (I also replaced the fuse holder with a standard one for easier testing). Plug it back in, fuse blows again.

Any advice on how to proceed? I'm running out of 1 amp fuses and parts I could replace. visually there is nothing else wrong with it. I measured a few parts with my multimeter but they seemed ok. if it's the actual coil/inductor I'm out of luck because I don't have anything similar to the one in the circuit.

circuit SN is KB3151 (A) and the regulator chips is the 10 watt SD4841 (and not the 15 watt SD4844 what comes with some models ). attached an image of the circuit.

saw someone on here fix theirs with a simple recap but seems like I wasn't as lucky
 

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Terryl

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Using an ohm meter, try measure across the AC power input (with a new fuse and the unit UN-plugged) then please post the readings back here.
 

Terryl

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Also the big yellow rectangle at the bottom left of the PS, may be a MOV, (side photo of it may help us) it may be shorted out due to an overload on the AC input, look on the bottom of the PCB and see if it ties across the AC power input pin's, if so then try removing it, see if this fixes the problem.
 

jeallen01

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Assuming that the Openbox uses a generic 12V AC/DC adapter (most similar boxes do - my Openbox V7 does), then take the "easy way out" and buy another generic adapter - just make sure it has the same-sized DC input connector (most do) or else use a size adapter!

In my case, I have a couple of AC/DC 12V 8A CCTV adapters supplying several boxes of various types in both the "office" and the lounge - couple of other sat boxes including the SX88 - and previously a Freesat V7 and the Openbox, in the office, and a Netgear GB switch, and then another one supplying the SX88+, an old WD streamer and another Netgear switch in the lounge. There's still capacity to spare in both cases!
 

Terryl

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The S10 Openbox has an internal power supply, see his photo in the first post.
 

istvan

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Using an ohm meter, try measure across the AC power input (with a new fuse and the unit UN-plugged) then please post the readings back here.

it's basically an open circuit, 12M ohms of resistance. the yellow rectangle is an MPX275-X2 safety cap. removed it but it seems fine out of circuit. -1 fuse. maybe it is the coil, and it only shorts once the driver kicks in.

and yeah, the psu has +5, +12 and +24V rails. I can supply 5 and 12 just fine but not really the 24V for (presumably) the LNB...
 

jeallen01

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The S10 Openbox has an internal power supply, see his photo in the first post.
That internal PSU is on a separate PCB/PWB with an easily identifiable DC o/p connector, and thus fit a suitable i/p socket in the case with a 2-core cable between that and the PCB/PWB connector - the issue is to determine the o/p polarity of the board connector, probably by tracing the rectifier(s) and large smoothing caps in the secondary ccts, and then how they connect to the board connector.

OTOH, one can probably find, online, a 230/12VDC ( I very much doubt that the main circuit board requires anything other than 12VDC) PSU PWB/PCB with the same dimensions as the original, and fit that in it's place - still has the polarity issue though.

Edited: Just read istvan's latest post - MORE complicated, but boards with 5V/12V/24V outputs are almost certainly obtainable.
 
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Terryl

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Hummm open circuit, that's not good, it may be beyond repair.

If you can find a 48 or 36 volt supply you can build your own,(if your handy) a 24 volt, 12 volt and 5 volt regulators are not hard hard to find, nor is the circuit to put it together.
 

Terryl

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Exsiting PS has +5, +12 and +24 volt rail's, the 24 volt is to the LNB power supply, it needs to deliver +18 and +14 volts DC to run the LNB.
 

istvan

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Hummm open circuit, that's not good, it may be beyond repair.

If you can find a 48 or 36 volt supply you can build your own,(if your handy) a 24 volt, 12 volt and 5 volt regulators are not hard hard to find, nor is the circuit to put it together.

welp, thanks. I'll probably shelf it for now because the local electronics shop that I frequent is still closed. I could try it from the lab bench power supply but that wouldn't be too practical + I'm pretty sure the main circuit is fine. A quick search on ebay didn't give me any power supplies that were the same but I'm sure I could find similar ones.

The old power brick for my printer is 36V iirc. I could put 3 regulators on a perf board and convert it to a DC barrel plug input. It's a fixed dish so I don't need the extra power for a motor anyway. just have to get a 24V regulator and some heatsinks.

(bonus image of the power out connector attached.)
 

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Terryl

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A 36 volt power supply should work, the only unknowen thing is how much DC current each rail needs, that would be a tough one to solve out, you maybe can work out the supply current from the old PCB, or take a look online to see if someone has posted the spec's.
 

istvan

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A 36 volt power supply should work, the only unknowen thing is how much DC current each rail needs, that would be a tough one to solve out, you maybe can work out the supply current from the old PCB, or take a look online to see if someone has posted the spec's.

It seems like the biggest cap/diode are both on the 5V rail which would make sense since almost all modern circuits use 3.3V or 5V (and probably convert it down to ~1V for the main IC). Decoding HD takes a fair bit of power but it's doable with a good quality regulator. The 18V is for the LNB, that's for sure. The 12V is used for the LAN port (I can't think of anything else that uses 12V. maybe they're sending 12V to the LNB to select the vertical mode, but that's almost out of specs so probably not)
 

jeallen01

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More difficult to find than I thought - but the board out of one of these might work
 

istvan

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More difficult to find than I thought - but the board out of one of these might work
Good call. I'll look around if I can find any at a decent price. At least I have a keyword to search for now - Triple Output Power Supply.
I might get one of those cheap sat boxes from ebay for $20 in the meantime. it probably won't be great but it'll work while I fix this one up. My old skymaster dx 23 can only do SD and puts HD channels under "radio" so that's a no-go.
 

jeallen01

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OTOH, this UK site is offering a Openbox S10 for £45 wholesale, but there may be others??
 

istvan

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OTOH, this UK site is offering a Openbox S10 for £45 wholesale, but there may be others??

got mine for £6 used. no one else bid on it - for the price it was as good as one can get but for £45? I'd rather pick something with less known issues ;P

Dropper resistor.

could work. an LNB takes like, what, 100 mA? @ 18V that's 1.8W, would need some beefy resistors who.
 

jeallen01

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got mine for £6 used. no one else bid on it - for the price it was as good as one can get but for £45? I'd rather pick something with less known issues ;P...
Didn't realise how old that box is! Probably better to look for something a lot newer and better :rolleyes:
 
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