Interesting Fault on Satellite Reception
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Interesting Fault on Satellite Reception
by Peter Brown Tue Jul 17, 2018 4:36 pm
An intermittent fault developed with Satellite reception on my AVTEX L188DRS whilst in Europe. We weren't watching that much TV so didn't take it to task but did keep nibbling at it. I eventually found that the voltage supplying the LNB was dropping below operational threshold, switch off or to terrestrial TV for a while and it was restored for a while before dropping again.
As and when I tested all the power and aerial connections and couldn't find the problem, I was beginning to think the TV had developed an internal fault. I then remembered that when installing the TV I'd lengthened the power cables by crimping in extra length of wire, I'd done this before buying a ratchet crimping tool. I put my hand to the back of the TV cupboard, located the crimps and felt one was warm!
The extra current drawn by the LNB was causing the poor crimped joint to heat, increasing its resistance and dropping the voltage below that required to power the LNB. Switch off the LNB, it cooled and resistance dropped again. I nipped up the crimp with the ratchet tool (not a five minute job because of location) and all is now well.
As and when I tested all the power and aerial connections and couldn't find the problem, I was beginning to think the TV had developed an internal fault. I then remembered that when installing the TV I'd lengthened the power cables by crimping in extra length of wire, I'd done this before buying a ratchet crimping tool. I put my hand to the back of the TV cupboard, located the crimps and felt one was warm!
The extra current drawn by the LNB was causing the poor crimped joint to heat, increasing its resistance and dropping the voltage below that required to power the LNB. Switch off the LNB, it cooled and resistance dropped again. I nipped up the crimp with the ratchet tool (not a five minute job because of location) and all is now well.
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Re: Interesting Fault on Satellite Reception
by Eltel Tue Jul 17, 2018 11:06 pm
Yes I’ve encounterec that problem in the past
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Re: Interesting Fault on Satellite Reception
by meanchris Tue Jul 17, 2018 11:30 pm
Picture the scene:
I'm standing looking at a three phase circuit breaker, behind a plastic safety cover, carrying 1500A per phase, at 585V.
One of the incoming cables is blackened from the crimped lug on the CB terminal, and there's a wisp of oily smoke rising from the case of the circuit breaker.
If the gases being generated by the overheated insulation reduce the ionisation voltage threshold across the gap to the adjacent phase then, even allowing for the upstream 11KV circuit breakers, (which I'm dubious about, as I have suspicions that the HV company engineer doesn't really know what he's doing}, the explosion right in front of my face will be like a bomb going off.
Nobody that I ask is willing to shut the machine down, nobody knows where the 11KV switchgear is...........
Similar to Peter's experience, just scaled up a little bit.
I'm standing looking at a three phase circuit breaker, behind a plastic safety cover, carrying 1500A per phase, at 585V.
One of the incoming cables is blackened from the crimped lug on the CB terminal, and there's a wisp of oily smoke rising from the case of the circuit breaker.
If the gases being generated by the overheated insulation reduce the ionisation voltage threshold across the gap to the adjacent phase then, even allowing for the upstream 11KV circuit breakers, (which I'm dubious about, as I have suspicions that the HV company engineer doesn't really know what he's doing}, the explosion right in front of my face will be like a bomb going off.
Nobody that I ask is willing to shut the machine down, nobody knows where the 11KV switchgear is...........
Similar to Peter's experience, just scaled up a little bit.
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