Faulty TV aerial distribution amplifier?

Hi, I've question if anyone can help...
About 3 or 4 years ago we had our house extended and had a 6-way distribution amplifier fitted in our loft to boost our analogue TV picture and split it to different rooms in the house. The picture was then near-perfect in all rooms.
A couple of months ago the picture quality started to deteriorate, and is now poor.
When I plug the loft aerial straight into a TV set (in the loft, for testing purposes!) the picture is brilliant. When I plug the aerial into the amplifier and connect the TV to one of the amplifier outputs, it is poor (but not as poor as downstairs, presumably due to cable losses).
My question is: can these distribution amplifiers "go wrong"? If so I obviously need to replace it. I've seen a reference to distribution amplifiers needing replacing after a storm. Is the a possible cause?
Obviously I don't want to spend money on a new distribution amplifier if that's not the cause.
Many thanks if you are able to help.
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What you describe is typical of the amplifier having lost its power supply, and the signal is just what's capacitively leaking through the unit. Does it make any difference if you actually switch the power to it off?
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Andrew Gabriel

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writes:

Thanks for replying... The power is definitely on, as the on/off switch lights up, and when you switch it off there is no picture at all. I should add that I've managed to get one TV to have a reasonable picture by connecting it up to the single "Full" output. But even then it's not as good as if I bypass the amplifier altogether.
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Have you tired disconnecting all the outputs, then trying to connect just one (and if that is a bad picture, try another port, then if that is still bad, try another run to a different room?)
Just thinking maybe one of the outputs has got shorted, and this is dragging the whole lot down?
Sparks...
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I mostly did my testing using a portable TV in the loft, firstly plugged into a spare output, and then having unplugged all the other outputs. Didn't seem to make much difference. I don't think I tried it in every one of the outputs, though. What causes shorting? (Just occurred to me that as my aerial is in the loft, a storm seems an unlikely reason??)
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Shorting could be caused by nailing through a cable, or a crap connector at one end (or a fault in a TV/VCR Etc.)
If you tried a few, with all other outputs disconnected, it sounds like the unit has failed for whatever reason.
Do you have a mast head amplifier too (another box of tricks, usually right next to the Ariel)?
Sparks...
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Not sure about the masthead, will check it out when I can, won't be for a day or two though. But as I said, the picture is fantastic when I simply bypass the amp unit. Thanks for your help thus far, I'm inclined to try replacing the amp box.
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wrote:
|
| | > | >>> | >> I mostly did my testing using a portable TV in the loft, firstly plugged | >> into a spare output, and then having unplugged all the other outputs. | >> Didn't seem to make much difference. I don't think I tried it in every | >> one of the outputs, though. What causes shorting? (Just occurred to me | >> that as my aerial is in the loft, a storm seems an unlikely reason??) | > | > Shorting could be caused by nailing through a cable, or a crap connector | > at one end (or a fault in a TV/VCR Etc.) | > | > If you tried a few, with all other outputs disconnected, it sounds like | > the unit has failed for whatever reason. | > | > Do you have a mast head amplifier too (another box of tricks, usually | > right next to the Ariel)? | > | > Sparks... | > | Not sure about the masthead, will check it out when I can, won't be for a | day or two though. But as I said, the picture is fantastic when I simply | bypass the amp unit. Thanks for your help thus far, I'm inclined to try | replacing the amp box.
If you do IME one with "F" connectors is much better than the normal TV connectors, and if you end up changing coax, use Satellite grade, with copper foil and copper braid which is IME much better.
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Dave Fawthrop <dave hyphenologist co uk>
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On Sun, 09 Oct 2005 08:31:21 +0100, Dave Fawthrop

Along these lines, you can get distribution amplifiers with a number of built in outputs on the box and a high level output.
This be connected to passive splitters (very inexpensive - about 3) perhaps located closer to several sockets on the ground floor or first floor. The advantage is shorter and easier cable runs.
http://www.teldis.com/CP-Taps&Splits.htm
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Timbo expressed precisely :

After reading your other submission, it does sound as if the unit has failed. Certainly they can suffer storm damage (lightning). Even if not a direct strike, it can damage the front end.
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Thanks. Just occurred to me that as my aerial is in the loft, a storm seems an unlikely reason??
I wonder if it has just partially failed due to a component or something.
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Timbo formulated the question :

Most likely the actual amplifier, the FET. Look for a component which looks like a transistor... Three legs, probably black plastic cased. If you can work out the part number on the side, then it should be possible to buy a replacement. Not a guaranteed fix, but it is difficult diagnosing at a distance.
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Thanks Harry.
I'm a complete novice at that sort of thing, so I think I'll probably try replacing the whole unit - thanks for all the help!
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On Sat, 08 Oct 2005 22:39:31 +0100, "Harry Bloomfield"

Are these tiny ? My amp has gone a bit iffy recently, although cycling the power and/or wiggling a few of the leads around seems to restore normal operation for a time. I opened it up expecting to see a decent set of circuitry and maybe the odd suspect component, and found hardly anything inside !
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Yes. Some of the RF transistors have a nasty chemical in them. Can't remember what it is, but the datasheets have dire warnings about breaking them open, disposing of them or burning them.

One transistor, a few tiny capacitors and coils is quite typical. Some of them use one of the hybrid RF amplifier modules.
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On 08 Oct 2005 22:31:47 GMT, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

Beryllium oxide.
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On 8 Oct,

Mainly higher power devices in the '70s and possibly '80s. More modern devices are usually Beryllia free.
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Mainly RF power devices, not small signal amplifiers.
Dave
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Frank Erskine presented the following explanation :

You will only find this in the high power devices where heat needs to be got out of the device quickly - transmitters, not in small signal amplifiers such as the item in question.
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On Sun, 09 Oct 2005 11:34:25 +0100, "Harry Bloomfield"

[scratches head]
I'm still trying to work out how a simple question like "are these tiny" led off so quickly into a discussion about dangerous chemicals...
(Don't worry - I'm not new to Usenet :-))
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