Lost signal on DM500s

[MORA]

A week ago or so my DM500S lost signal.
It have done it before and usually works after refitting the cable.

But not this time, I have tried refitting both ends still nogo.
40-60% signal in first bar 0% in second bar and 5000+ in error.

I flash erased and flashed the new gemini image, still no help during scan it showed 20-30% on second bar on a few transponders but found 0 channels.

I know the cable works, since my computer can use it without problems, and I have tried the dreambox in another connection that works with a regular reciever.


Is this a hardware problem, and if so is there anything I can do myself (The box has warrenty, but the seller is an idiot that will take 3monts+ to fix it) ?

[Slap]

What cable do you mean,is it the LNB cable as the PC has nothing to do with the 500s when you are scanning for channals.Is your Dish pointing at the Sat that you are scanning.

[MORA]

The lnb coax cable yes.

The dish is ok since 2other recievers work on these lnbs (dvb-s card in my computer and a original nds reciever)

[J700]

If my dreambox lnb voltage output gets overloaded the SNR drops to ~50% and AGC drops to 0%. I have to disconnect the power supply to get it working again.
People have reported that Q72 transistor inside dreambox fails because it is undersized. The lnb current limit (accomplished with Q72) is 500mA and the max current rating of Q72 is :eek: 500mA. I theory Q72 could be removed and hotwired because a LT1930, that makes the 13/17volts from 12V, has an internal 1000mA current limiter.
_http://www.linear.com/pc/productDetail.do?navId=H0,C1,C100 3,C1042,C1031,C1061,P1813
What you could do without loosing your warranty is to measure the voltage on the LNB-IN connector. 13-18Volt is fine, anything else -> send it in for repair.

[MORA]

Ok, I just checked the voltage, and acording to my volemter its broken.
Its not so precise at low voltages, but 12V does not lit up so its well below 12V (a 9V battery will lit up 12V).

It does indicate a connection though.
So its a repair ?

[Lawsy]

Exact same problem. I know my cable and dish work as it is all fine when i hook up my relook.

I will test the voltage.

Any one on here offer repairs ?

Cheers

Lawsy

[J700]

There is a quick'n'dirty fix for this. Bypass Q72.
Q72 has three pins. Voltage between these pins and chassis is +5V, +12V and +12V (showing 0V if Q72 is broken). Connect the +12V pins together.

[Lawsy]

Any chance of a diagram for which pins need joining ?

Thanks for your help anyway.

Cheers

Lawsy

[Lawsy]

Hi,

just put a meter over q72 and its showing 12 v on the 2 pins and 6 v on the other. So seems no problem. 0v on the lnb in.

ANy clues anyone. I have looped through from my other receiver and the tuner is picking up a signal.

If i cannot get any solutions what about the following?

3 scenarios :-

if i had a vbox would this allow my dreambox to work as it would power it up

If i had a twin lnb with one going to my relook and one to my dreambox, would the relook 12v liven up the over feed.

Can i provide 12v from another source, ie seperate power supply hooked up to the coax

Cheers

Lawsy

[J700]

Check U70, it's a lt1930 step-up dc/dc-converter. Also check diode and inductor next to it. Measure the voltage at the LNB voltage pcb testpoint (marked solder point).

I suspect that the dreambox dm500 lnb-voltagesupply circuitry consists of three transistors and on dc/dc-converter. One trasistor is used to shut off the lnb-voltage at standby, another one handles the 500mA current limiter (Q72) and a third one to switch between 13 and 18Volts (polarisation). The dc/dc-converter is used to lift the 12V voltage to 13 or 18v, it's a lt1930 switching regulator at 1,2MHz and can handle up to 1A.

[Lawsy]

ok,
after all the mucking around. this happened. initially hard to get a 12v reading on q72. then it lit up. LNB now working . Could be a dry joint ?.

Any reasons it could just start working ?

Mick