DM800-HD Over heating Mods

[alunfennell]

Whatever happens after 18 months of exploitation of DM800 HD (with and without a cooling fan)

There are three versions of DM800 HD PVR:

1) original versions with a serious flaw - overheating [small series], as seen here:



2) with an attached external capacitor to remedy the flaw, as seen below
3) the capacitor is integrated into the tuner

Below, we have the first version of the tuner, REV:J, withdrawn by DMM, then modified [as you will see a bit later on, with a 22uF capacitor and a 220 Ohm resistor], plus the third version, REV:K, which has an added SMD capacitor built into the board, as seen on the image.





Just so there's no "you're imagining things".... from the tribal lot...

Here, we shall compare 2 DM800 HD's from the second series, both from May 2008, with a modified tuner, the ones with an added 22uF capacitor under the tuner itself, modified by DMM.

The first image is a measurement of internal resistance with ESR meter. It was taken in DM800 with an internal 12cm cooling fan, added by me, after 18 months of exploitation. As one can see, the value is 1.3 Ohm, slightly higher than a brand new one

http://wiki.xtronics.com/index.php/Capacitors_and_ESR - see the detailed info here

The second image shows a second DM800 HD tuner, also used for 18 months but without any cooling fan installed.

It's a disastrous state of affairs: because of the overheating, the internal resistance grew to 64 OHM and the capacity fell from 22uF to 6uF.

The consequence: the infamous "TUNE FAILED" and the disappearance of any signal, which led to a complete malfunction of DiSEqC switch.

Which is why this particular DM800 HD PVR came to me, in the first place. The owner hasn't installed a fan and learned to live with the fact he had to switch the receiver off a few times, in order to finally manage to move to another satellite... until he couldn't move it any more...

Back then I advised everybody to install a cooling fan. Those who listened are safe now. Those who didn't - oh, well...

If one decides to change those parts...

One ought to be very careful, as there is a tiny resistor [220 OHM], that must be removed before you change the capacitor and then returned, once the new one is in place. Its lower part attaches to the transistor and the other to the capacitor itself.

Here it is, so one doesn't say "I wasn't warned"...



One more observation: the seriously loudly advertised OLED display has a bit of a shortcoming - it doesn't last! Here is an image so one can judge for oneself. Btw, have a look at yours. I bet it doesn't look any better....



Thanks to BEBI for this Tut & Demo

Regards:
Alun

[Fergal]

Mine is opposite from most boxes
when i boot my box up from cold the HD channels dont work (tuner failed message) but after 10 minutes they all work fine no glitching at all
if i switch the fan on which sits on top of the heatsink under the tuner after about 5 minutes the hd channels start to glitch again,
its as if the tuner needs to be warm/hot for the hd channels to work
would it be a dry joint somewhere or would doing the mod you suggested cure the problem.
Thanks