I'm looking at the trace width coming from LNB controller to RF connector, and I think it's too narrow.

It looks like 3-4mil (75-100um) wide.
I'm not sure how thick the copper layer is.
But if it's standard thickness (1oz per square inch), rated maximum current for this width of trace is about 400mA.

I assume, software is limiting output current of LNB controller (it's LNBH21P) to 750mA.
For such current, trace should be at least 8mil wide (200um).

is it another hardware bug on DM side?

I'm talking about trace between pin B1 of connector TU1400_A and pin B1 of connector TU1400.
Tuner module is soldered into connector/socket TU1400_A, and LNB power is supplied through this pin (pin B1).

My assumption:
during design, TU1400 assumed to be a main tuner connector (for a raiser interconnection board, where plug'n'play tuner module is plugged in, as on all other DM models).
And pin B1 is receiving the power (through "beefy" line in some intermediate layer).
TU1400_A is a "back-up" solution (to solder a non-replaceable tuner module, instead of plug-n-play raiser board).
But someone who did a board layout forgot that trace between B1 pins should be a bit thicker then all other similar traces between these connectors (it's not just signaling line, it's a moderate current bearing line as well).

It's possible that there is a "back-up" trace between B1 pins in some intermediate layer.
But being a PCB designer myself, I know that most PCB design software packages "automatically" remove these duplicate traces during layout process. From my experience, there is more then 50% chances that this "back-up" trace does not exist.
Also, this backup trace in the inner layer should be twice as wide as the trace on the outer layer (cause inner layers use thinner copper slab, and passive heat radiation is obstructed by the insulator).
But I can not prove this without vandalizing the board. That's why I started the topic as a question (not an arrogant statement).

To be safe then sorry, I soldered a wire jumper between B1 pins on the back of my DM500HD main board.
Just in case....

PS: I don't encourage other users (who do not have soldering experience) to do what I did. You may ruin your board (and loose the warranty during this process).
If you have a heavy load on the other end of coax-cable, use power inserter (or powered switch). This would keep your warranty intact.

Zitat von Olove

Okay, your assumtion is simply plain wrong.
TU1400 is a test header and no main connection.

huh?
what this has to do with what I was saying?
TU1400 may be a test connector, not a big deal. It does not change the conclusion which I stated above.
Check the positions of these connectors and the traces coming to them.
For instance, all traces from MPEG bus are coming to TU1400 first, and then (on the other side of the board) from TU1400 to TU1400_A.
Besides one power line (probably 3.3 or 5V) there are no traces which come directly to TU1400_A (and then from it to TU1400).

If you cut a trace (I'm not offering to do that, I just give an example of signal continuity) coming to TU1400, you will automatically loose a connection with TU1400_A (where tuner module is soldered).

One more thing which I forgot to mention (and which actually caused me to look into all this business with LNB line).
there is a rather wide trace between B2 pins of these two connectors (this is a width of trace which I expect to have for LNB line).
But the problem is: LNB voltage/current is supplied to tuner board through pin B1 (not B2).
B2 pin is physically connected to the circuit (of LNB controller) which is responsible for listening for Diseqc response from periphery (DSQIN pin of LNB controller; this is high impedance input).

That's why I ended up with a guess that someone set the widths of traces incorrectly (put a wide trace on diseqc feedback line, and narrow trace on LNB out line - it should be other way around).

PS: B1 and B2 pins are not shorted together (there is about 10kOhm impedance between them).

my intentions were to prevent a problem