Dreambox 500S tuner looses signal after a min

[Per Hansson]

Hi, I've got a fairly old DM500S

It's been working fine up until now, it's only connected with a straight cable to the dish. I.e. no switches etc...

After about 2 minutes the SNR and AGC which is at ca 85% for both becomes erratic
It goes to 0>23>50% and back and forth etc. With both Gemini v2.90 and v3.50 the box crashed and restarted now...

I put in the latest DMM image "rel109-20060803.img"
With it the signal becomes erratic just like explained above but then it settles down at ca 28-30% SNR, 0 AGC and with the BER going up and down a bit... It does crash after a while tho (but not reboot like with Gemini)

Now if I warm reboot the dreambox when the signal has become erratic but it has not yet restarted itself I don't get any signal upon bootup, it is erratic just as before... (Correction; if I restart when the signal is erratic I don't get any signal again, or rather it continues to be erratic, but if I restart when the signal has settled down at ca 30% SNR I actually do get a good signal again, for like 2 mins then it's all back to square one)

If I remove power for 10 sec to cold boot it I do get a good signal, 85% SNR for like 1 or 2 minutes, then it becomes erratic again...

I have tried cutting of the coax cable on both ends so I get "fresh" ends but it didn't affect anything at all.

I also have another dreambox, connected to the same twin LNB, but with a switch for another LNB too, I connected the DM500 to this coax cable instead and the issue was exactly the same...

It seems to me like I may be loosing LNB power or something similar, because the tuner obviously isn't dead... Can someone provide some points to measure voltage etc? I've already checked the ESR of all caps and they where within spec, however I don't particularly fancy the brands DMM choose. But in quality vs money income we all know who wins

I should also mention that I tested to run the box without a coax cable playing up recorded TV shows via network for several hours without any issue at all...

[jenkki700]

I got the same symptoms sometimes if my moteck motor pulls too much current.

[Per Hansson]

Ok, my thinking is that the dreambox is sending out too little current to the LNB, or rather that the component that does send out that current fails after a min...

Can anyone provide any measurment points inside the DM500 to check for the LNB voltage?

Btw, I tried putting my DB7000 on the same cable, (in stand-by mode) before the DM500. But it did not make the signal get stronger (Automatic Gain Control was still at ca 85% on the DB500)

[mvdig]

Satellite Configerations you can Increase Voltage...and you check another LNB

[Per Hansson]

Thanks, but I've already tried another LNB

it made no difference

And since I was using the dreambox connected directly to the LNB (no diseq) there are no options for voltages etc, and it has been working fine for about 2 years so... (i.e. there where no changes done to anything when this issue started)

I'm using a Invacom Twin LNB 0.3db 031 is the model numer if I remember right... But as I said I also tried with another LNB and there was no difference...

[viairdeto]

Can you try your dreambox in a friends house?
This could be almost anything, all from a bad image installation (you've used dreamup to install your image, right?), to faulty cable (you never know, even if you made a fresh cable, you can have an interruption somewhere in the middle of the cable), the LNB (but you've tested that one) or that your power supply is getting bad. So if you can test your box at a friends house, use both your friends and your power supply.

[Per Hansson]

viairdeto; thanks for your reply, I had already tried eveything, other cable, other LNB etc etc...

So I went over to a friends house, ran my dreambox using his powersupply (same model no, he also has a DM500-S)
It worked just fine...
But since I had pretty much already ruled out the PSU as being faulty (my dreambox worked fine with it playing a movie over the network, it was only when I used the tuner that things went bad...)
Anyway, I fired up his dreambox using my powersupply, it ran just fine too, for 17 hours. No issues at all...

So then I tried to go back to using my original powersupply, crashes instantly when watching a satelite channel via the tuner, but no problems streaming a saved movie over the LAN. To say the least I was confused now

Because my dreambox did not work with his powersupply, therefore pointing to it as being faulty, but his box did work just fine with it!

Anyway, I took my dreambox home, and the faulty? powersupply, took an old ATX computer powersupply and wired up the dreambox to run from it. And it's been running for 19 hours now without issues!

So the issue indeed is with the powersupply. And after some further investigation it is the main filter cap (400v 33uF) that is bad, it has an infinite ESR so there is no connection at all in it... (it's not bulging)

This still does not explain why my friends dreambox is fine with running from this shitty powersupply, perhaps his (rev2) vs mine (rev1) DM500 simply has a better built in DC-DC filter stage so it does not matter all the ripple current that powersupply must be sending out... (it's voltage is within spec even with the dreambox as load. 12.08v...)

This is just a small warning for other people that have the same PSU, it's labeled as Potrans I.T.E Power supply model no: UP01281120 The PCB is marked UP01541X

[Per Hansson]

Got my new cap now, made quite the difference
The failure of the old cap was that one of the legs had lost it's connection with the film, so it was not doing anything good at all (the film still had a healthy ammount of electrolyte so it had not failed of age or poor manufacturing as I first suspected)

The old cap was a Ltec 400v 33uF, the new cap is a Sanyo FXS 400v 47uF low ESR cap. Which is also 4mm thicker. I'm sure it will fare quite a bit better in normal usage cenarios (i.e. with a few power spikes and surges now and then) (it's artno 67-141-33 on elfa.se incase anyone wants to know)


Top, original cap, bottom, new Sanyo cap. Who said size doesn't matter?

[brandon7gr]

I had the same problem as you ... i changed the wire ... and suddenly it works

Many thanks because this topic helped me a lot to find that the problem was electrical

[x 5]

Originally Posted by Per Hansson

viairdeto; thanks for your reply, I had already tried eveything, other cable, other LNB etc etc...

So I went over to a friends house, ran my dreambox using his powersupply (same model no, he also has a DM500-S)
It worked just fine...
But since I had pretty much already ruled out the PSU as being faulty (my dreambox worked fine with it playing a movie over the network, it was only when I used the tuner that things went bad...)
Anyway, I fired up his dreambox using my powersupply, it ran just fine too, for 17 hours. No issues at all...

So then I tried to go back to using my original powersupply, crashes instantly when watching a satelite channel via the tuner, but no problems streaming a saved movie over the LAN. To say the least I was confused now

Because my dreambox did not work with his powersupply, therefore pointing to it as being faulty, but his box did work just fine with it!

Anyway, I took my dreambox home, and the faulty? powersupply, took an old ATX computer powersupply and wired up the dreambox to run from it. And it's been running for 19 hours now without issues!

So the issue indeed is with the powersupply. And after some further investigation it is the main filter cap (400v 33uF) that is bad, it has an infinite ESR so there is no connection at all in it... (it's not bulging)

This still does not explain why my friends dreambox is fine with running from this shitty powersupply, perhaps his (rev2) vs mine (rev1) DM500 simply has a better built in DC-DC filter stage so it does not matter all the ripple current that powersupply must be sending out... (it's voltage is within spec even with the dreambox as load. 12.08v...)

This is just a small warning for other people that have the same PSU, it's labeled as Potrans I.T.E Power supply model no: UP01281120 The PCB is marked UP01541X

hi m8 had exacly the same prob and your post help me to sort it out fast,trayed with another powersupply and works like a charme tanks m8