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sidha said:

I lost a port on a 4-way DiSEqC due to a momentary short caused by me changing an lnbf with the system active. A voltmeter proved that port 4 would not pass DC power to the lnbf. Inside, I found a tiny surface mount dual transistor that had failed. I replaced it with a part robbed from another DiSEqC switch that died in a worse way. While troubleshooting to narrow down what exactly was damaged inside the switch, I discovered another problem. Port 1, 2, 3, appeared to function normally when addressed. However, port 2 and 3 would continue passing some power to an lnbf even when another port was addressed and active. About 5 volts continued to flow into the lnbf's on those ports, contributing to an invisible additional current drain. In some borderline situations the total current draw can lead to instability, depending upon how complicated the system and length /quality of cable. Obviously, when using port 1 or port 4 on my switch, the semi-active state of port 2 and 3 would be reducing the available current required for proper operation of a dish positioner and/or cascaded 4-way switches. I see a real need for a simple device for testing DiSEqC switches.

I hope this information helps someone experiencing trouble with blind scans and command related hardware malfunctions. There is no current limiting protection inside these switches. All it takes is a brief short on the center wire of the coax while connecting to the lnbf. You may not notice anything was damaged, but that doesn't mean it didn't happen. Each of the four ports is isolated from the other, DC and RF(lnbf IF), at all times. In my situation, the DC switching failed on three ports-- one totally, the other two partially. There are also PIN diodes that pass the RF from the lnbf selected. Damage along this component chain will cause a drop in signal strength due to RF loss, directly and adjacently. But, it takes unfriendly voltage surges, not shorts, to damage those devices. I've only had one DiSEqC switch suffer lightning damage that completely fried one port, RF and DC, and the command chip, but it left me three good ports with spare part RF and DC switching components. Why bother to analyze and repair such cheap devices? Because, I can. And, I'm working on modifying a Dishnet SW-21 switch so I can use it with my Pansat, as a 22K switch. I may actually watch TV sometime. A hate the fact that this is a throw-away society, but I sure benefit from all the discarded equipment in a major way. I just acquired a very nice 2 meter composite KU dish w/Norsat lnbf that the commercial property owner was glad to see go. This is a great hobby on many interesting levels!

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ken2400 said:

I wonder if I disconnect the cable from the receiver, do my cable switching, then connect the receiver back up if it would help keep the switch from dieing.

I have one now that has a port out.

Thanks for info.

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