No LNB voltage on tuner connector - how or where is voltage generated?

[LeroyPatrol]

More of a general question. Just wondering if a tuner module isn't putting out the lnb voltage where the problem usually lies? Going by other posts it seems the voltage is generated externally to the tuner module. Am I correct in this asumption?

Leroy

[Frannie]

yes....generated externally.

[puca]

not sure on other boxes but with umax if there is no lnb output it is the power supply dying normally cap c9

[gw1]

It depends on receiver. Some receivers have power supply on the tuner PCB. But most DM500 clones have a [190K PDF] on the motherboard that generates the LNB 13/18V supply fed to the tuner module.



LNB power control (on/off) is driven from processor pin AC5, while the 13/18V control comes from processor pin D18.

The generated 13/18V gets fed to the tuner on pin 2:



Other older receivers like Humax nearly always have the power generator on the motherboard, outside the tuner module. The older circuits tend to be more complex though. I won't post Humax power supply here because it spans several pages of a large PDF.

Puca's point was that lack of LNB voltage often indicates failing switchmode power supply. Checking the output rails of power supply board with a voltmeter (with LNB load connected) usually indicates if there's a problem.

It could also be caused by blown fuse in power generator circuit, and sometimes by a damaged tuner. If you can see 13V or 18V DC on one of the tuner input pins but not on the tuner's output connector then it's the tuner that's faulty.

[best4less]

I have fixed heaps of tuners with no power for LNB

Replaced the tuner on only one (7020) the rest have been Diodes regulators or something in the PSU