Snowy Picture

I have an intermittent problem with my TV that I just can't figure out. Often the picture on my TV will slowly degrade and become snowy; to temporary fix this all I have to do is unplug the signal cable and immediately reconnect it. When I do this the picture will instantly be clear and sharp. But then it will slowly degrade again and after about 10 or 15 minutes the picture will be so snowy it needs to be "recycled" again. But this annoying pattern of having to disconnect/reconnect doesn't happen all the time. It seems to be worse in the mid to late afternoons and early evenings. Late at night or in the morning it never (or at least very rarely) happens. On some days it doesn't happen at all. It also happens primarily with channels 2 - 7, not on the other channels. It's not the TV set--I swapped TVs and it had the same problem with the second TV too (a completely different brand). Anyway, does anyone have an idea on what can cause this build up of noise on my cable? Is there anything I can do about it? I asked the cable company and they blamed the TV set. As I indicated I doubt that's the problem since the same thing happens with a Sony and a RCA. Thanks.

Reply to
brian hughes
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perhaps two problems --- uneven bandpass indicates one problem: impedance mismatch. Snow that fades and rises indicates another problem: poor signal to noise ratio from charge on the signal lead. Since moving air can build up a charge, look around the set for any ionizers, fans (e.g. furnace blower) that push air over the set, blocked airflow vents on the set, etc. and move them away. Then there are some technical areas you can check.

1) most likely the ground for the antenna itself is open - the good reception at one end of the frequency spectrum of channels indicates the bandpass is skewed, and that usually is the result of no ground on the antenna, or a bad ground on a lead.

-especially if you have 75 ohm, the internal metal shield needs to be grounded.

in this area, it is possible there is some metal residue on the end of the coax, tiny bit - or that a bit of wire was caught and it is near the core when the end was crimped - replace it.

2) another possibility is that your have the wrong RG # coax for your application - not necessarily that you have 75 ohm called for and you are using 75 ohm wrong, but the impedance varies with type AND with length and frequency, so first if you use a 90 ohm or 50 ohm for a 75 ohm impedance, the bandpass will skew, or second if you use a long 75 ohm and at the higher fequencies the receiver sees the 75 ohm at that length and that frequency as 50 ohms, the bandpass will skew. 3) pinched coax that changes impedance or 300 ohm twinlead laying near a wire or metal that changes its impedance or can pick up spurious signal - for example, an ungrounded metal gutter on the south side in the sun will pick up charge, and that charge is using the coax/twinlead as a drain. Or the coax is stapled in and no longer is round, or staples are over both wires of the twinlead and creating a path for, or node that blocks, high frequency.
4) another possibility - it may be the same type chip in both receivers, and that chip may be sensitive to long leads, uses the ground on the wall to drain, etc. Crappy practice for an RF chip, but what can you say?

So check the wall outlet and circuit for tight ground contact (it's RF, not 60 cycle, so the gorund needs are slightly different.) If the wires run on a south wall, check the ground connections in the boxes. The constant warming and cooling of the sun may have worked the ground wires. If there is a metal downspout or gutter on the south side, ground it.

5) last possibility - circuit integrity - so no matter what you find here, use a surge protector at the set anyway. since many sets do not have a grounded lead, and they do build up charge, be sure the neutral in the box is bonded well to the gorund lead, and that the ground lead is solid, connector not corroded (don't take it off to clean it - use a jumper around the connector while cleaning and then pull the jumper after its all back together) If you have aluminum wire in that circuit - change those wiring connections, and be sure to use proper practice for al connections. If you have aluminum downlead, you may be screwed - it brings in power Ok, but in time it also brings in RF frequency hash from the micro-flashing, and the only hope there is to have a good box ground and use a very good surge protector at the equipment to shunt the hash..

hope it helps - (makes that time chasing grounds at BMEWS useful..... )

Reply to
Hobdbcgv

please notice we had the same exact problem here that you described and when we switched from regular cable tv to digital cable tv they had to completly rewiree the whole house including the line from the pole to the house and they did change to a new coax anyways we never have had this problem again, so it was something to do with the cable,,, and yes i would unscrew the cable from the back of the set and hook it back up and it would be fine for a while,, so i think it had something to do with the cable company running the sweep generator,, sure is a coincidence thats time warner for ya,

Reply to
KTLW _920

Thanks for the tips and info.

Brian

Reply to
brian hughes

Just a guess, but have you tried to adjust the set's AGC control? It's a bit of a stretch to believe that two TVs would share the same symptoms, but an AGC setting at the very edge of clamping can cause the symptoms that you describe, particularly if you are being fed signal via digital cable.

Then too I may be dating myself, because I'm not entirely sure that today's inexpensive, mass marketed TV models still have an adjustable AGC threshold level control in them.

Harry C.

Reply to
Harry Conover

Reply to
william_b_noble

We had the same problem.It wa caused by a croded connection at the cable Co.s box at the pole. JW

Reply to
John

You did not mention the model and make of the set.

This is usually attributed to a fault condition in the RF AGC, or the front end of the tuner. The AGC amp is usually located in the IF module output stage area, and the DC control coupling circuit for it is usually on the main chassis near to the tuner module in most sets.

The TV service centre would verify this using the proper test equipment, and determine if the fault can be serviced at the component level, or by changing the IF or tuner module to get the set working again.

Reply to
Jerry G.

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