LNB no power, switching off

[liveaboard]

After reboot, power to my LNB shuts off after a short time; seconds or minutes.
Even with no cables connected [just an electronic volt meter], I get correct 13vdc for a short time, then it cuts to nearly zero [measures .03v].

The box is old but still seems to boot correctly, plays recorded programs, and connects to the network. The only error shown is 'Tune failed'.

The problem started when I connected a new ivancom LNB, but that may have been coincidence. Before that I had an old offset LNB connected for a year, it worked but signal strength was low; so it had power.

Has anyone else had this happen?
Any hints?

[Trial]

Hi,
I think on my boxes is the max. power for the LNB written near the F connector. I think I saw 400mA. Perhaps your new LNB needs more.

Ralf

[liveaboard]

Thanks, but no, that's not it.
I was going to measure the current, but it switches off even with no LNB connected; I reconnected the old one, and it does the same.

[timofee]

If it is a power issue you could try to replace the capacitor which fails frequently and gives the "red light problem". This is the thread that explains how to replace the capacitor - https://www.world-of-satellite.com/showthread.php?26735-Redlight-of-Death-Repair

I have no idea if this would solve your problem, but is an inexpensive idea to try.

[liveaboard]

Thanks, but I'm sure that's not it.
I've changed that capacitor twice; each time the symptoms of impending failure was increasing system crashing, followed by failure to boot and the red light.
This time the processor is working fine; I can use it to watch downloaded video. The system hasn't crashed at all.
I'm leaning towards a literal bug; I don't have time to crack it open right now so I thought I'd ask if anyone else has experienced this odd symptom.

[cactikid]

I think i read of another user having tuning issues and identified another cap issue.Can you check these as that was his problem.

Started reading in the forums and found out that this is a common problem: missing the High-Band/Horizontal channels, due to dried capacitor! This causes the required 16V for upper band channels to not be generated properly.

*** Repair starts here ***

Changed a 100uF capacitor (C852) and... nothing.
Changed two 1000uF capacitors (C848 and C819) and... IT WORKED AGAIN!

*** Repair ends here ***

Hopefully might be of use.

[liveaboard]

That could be it; I don't think I'll have time to work on it for a few weeks, but when I do I'll look for those.
Do you happen to know the voltage of those 1000uF capacitors?

I'm going to be near an electronics parts shop next week.

[cactikid]

This was posted elsewhere
I've this on another forum and it's the problem that i have. Can someone confirm that is the capacitor marked C848 ?

"Hi everyone, not posted for a very long time.

Just to say thanks for this thread, fix my 5 year old Vu+DUO by replacing cap C848.

I had already replaced cap C807 about 2 years ago.

The problem I had this time channels were appearing "grey" in the channel list after a scan and there were only about 300 where I would get 600+. Selecting the channel I would get "Tune Failed". Tried changing images, satellite.xml, tuner configurations, some else's sat dish etc. nothing worked.

After replacing C848 with a 1500uF 10v @ 105C did another scan now up to 700 channels and my SNR has increased from about 45 to 70.

Thanks again."

[liveaboard]

good info, thanks.
I'll pick up a couple of suitable capacitors and give it a try.

[liveaboard]

Update;
We've been using the VU+ only as a video player, and it died, red light of death again.
In the meantime, I've picked up a handful of capacitors, so I opened it up.
I replaced C807 [the famous], for the third time, but that wasn't it.
I saw a blown 1,500 mf on the power board, changed that and its brother, no dice.
I changed all the caps listed by others above, and the box booted again [yay!], but as before won't power the lnb. it would power the light on my satellite finder, but when I connect the LNB [on the bench now], the power to it switches off and won't come back until a reboot.
I had some 100 mf caps left; so I changed 3 out of 4 100mf caps near the antenna connection block.
And it works!!

It will now power the 90ma single invacom, but when I connect the old invacom quad which draws more power, it still shuts off.
So far, this is still on the bench, I haven't reinstalled it all yet.

I suspect that most or all of the caps in the old VU+ are faulty; probably just a bit out of spec and fading. I find it highly unlikely that I just happened to luck out and hit the bad one[s].

I don't know if anyone else is keeping one of these old boxes alive; if so, just buy a lot of capacitors and start soldering.