"Let there be light" - or howto "marry" old car bulb and digibox

My VDR based digibox is great. Except one thing. The fan noise of old Compaq power-supply was quite big, so big that I had to turn off the machine every night. Well, I thought I could overcome the problem easily: I'll just buy new silent power-supply.

Ah; If life would be so easy, it wouldn't be interesting :)

Well, I went and bought a power-supply,  Nexus NX-3500. It's really silent and I was happy for a while.

- "But hey, what's that pixelizing I'm seeing now ?" I thought after installing the new PSU...

The pixelizing was always on the picture with certain channels that come in same MUX. No matter what I did, I even changed the motherboard and processor - no good, still pixelizing. Well, I ripped the case open and what the heck, it didn't pixelize anymore !?! So, when motherboard is on the floor, it worked quite ok. But it isn't so nice to look without the case :)

So, I thought it's something to do with RFI - maybe the new power-supply is radiating more RFI and the 2 digital cabel tuner-cards I'm using freak out with it. So, I went on and covered every power-cord coming out from the PSU with aluminum-foil... It was quite nice looking thing, unfortunately I didn't take any pictures of it then. But jolly to look at anyway, just like PSU from some B-class sci-fi movie :) But it didn't help, pixelizing was always there, no matter what I did (if the psu and motherboard were -inside- the case, that is). And every time the PSU was changed to old one, it worked like a charm. Hmm. This started really to piss me off.

Even stranger things were to happen. I was compiling new kernel to my box one evening, with new PSU installed and tuned to pixelizing channel. I didn't even notice it straight away, but it wasn't pixelizing anymore ! As soon as kernel was compiled, it started to pixelize again. How strange is that - the more you put stress on it, better it works ?! :) Things were getting interesting. I downloaded the "stress"-program for my box and ran it couple evenings. It hogs basically all the processing power, so the load is always 100%. The picture stayed fine !

Nice solution - execpt recordings could not be played back because all the processing power was consumed by "stress"-program.

After a while I took an oscilloscope and started to measure what's going on with the power-lines when there is some load on the system. For starters, the generated 12V and 5V lines are look totally crap with the scope. Fluctuation on by many kHz's and really messy stuff anyway. But I guess it's ok, after all it's the nature of the computer PSU's that make their output so "messy". Anyway, it seemed that voltages jumped upwards a bit when the load was 100%, to the 12.37V. No-load voltage was 12.30V. So I thought my old processor (PIII 450 Mhz) didn't load the PSU quite enough. After all, the machine is stripped down from any fans and "whirring" power consuming widgets. So, based on this, I put some small (about 7 pcs of 470ohm) resistors over the gnd and the +12V line - no good, I guess it needs to draw more current...

- "So, what draws more current and is silent?",  I thought. Jammed fan maybe ? No, they are too risky and besides I didn't have any fans at hand... A straight wire between the terminals ? Yeah sure, would draw a lot current and probaply burn the PSU on the way, so no good. Hey, what about old car bulb ? I had one for testing purposes anyway, so that's what I tried next.

It did the trick and now I'm having no pixelation at all and totally noise-free system :)

Only drawback is that now I must change the bulb in my digibox every now and then - but maybe that's the thing that separates this VDR installation from many others - not everyone has an old bulb in their box :)