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CTC 187 strange volume problem

I got a CTC 187 in with a complaint that after five minutes or so the volume gradually decreases by itself. I was thinking possibly tact switches but someone else said that it could be a bad eprom. I was wondering how one might go about isolating this problem?. I ran this set for a few days and never noticed a problem with the sound. I was about to call the guy and have him pick it up and suggest that perhaps the problem was the cable box when I mistakenly went to bed one night and left it running in the shop. I woke up the next morning and realizing that the set was on the first thing I noticed was that there was no sound coming from the shop. I took a look at the screen and noticed that every 2 or 3 seconds a volume bar would appear then disappear as thouh the set was being addressed by either the front panel tact switch or the remote. The volume indicator would show the sound to be all the way down each time it would appear as it indeed was. I tried raising the sound up and although the volume bar appeared and it did increment up it then afterwards immediatly slowly incremented down by itself.agsin. I haven't opened this thing yet as I really wanted to confirm his complaint first. Now that I have and considering what I've observed, does anyone think that the presence of the volume bar points to a leaky tact switch? Or could the volume bar and subsequent function activation be initiated by either a bad T chip or the processor? . I guess what I'm wondering is if there is any way that the set could produce a volume bar without the appropriate infrafed signal coming through the IR receiver or the chip being addressed directly through the tact switch? Thanks, Lenny

Reply to
klem kedidelhopper
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Unplug the IR receiver and tact switches ( P/J3001)then retest.

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Live Fast, Die Young and Leave a Pretty Corpse
Reply to
Meat Plow

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The tact switches seem to be the general consensus here. I really appreciate the advice. I have a theory on this problem that I would like to share. I also service commercial apartment house intercom systems. The apartment stations used in these systems are simply a 45 ohm speaker and three NO pushbutton switches. The switches are: "talk", "listen" and "door", (The last of which buzzes the front door solenoid to let people into the building.

Quite often I'm called out to one of these buildings to troubleshoot what seems like an impossibla weird problem. It may be that the lobby door solenoid is buzzing constantly, or perhaps the lobby speaker is crackling, or sometimes you find that you can listen to someones apartment constantly through the lobby speaker. Every apartment station sits on a three wire common trunk line so natually the occurance of any of these problems disables the entire building.

Many of these apartment stations use a form of a tact switch that just fails at tmes for no reason. Disconnecting that problem apartment station from the common trunk line in every case restores proper intercom function through the building. One particular 24 unit complex I service has four trunk wires in parallel each serving 6 apartments.Once I've isolated the problem down to a particular trunk line or group of six I will ask the building manager who the smokers are in those six apartments. Nine times ot of ten the problem switches are in the station that has been exposed to heavy doses of tar and nicotine.

My theory is that the smoke residue or the dust that clings to it must be conductive and therefore provides a high resistace short across the open switch. This has happened on more than one occaision so I don't believe that it is coincidence.

As it happens this TV customer is a heavy smoker too. The chassis had a thick "blanket" of sticky dust that I had to blow off with my vacuum cleaner before I could even put this on my bench. For fifteen years this guy has been blowing smoke at this set. I think that it finally suffocated. Just a theory. What do you think? Lenny

Reply to
klem kedidelhopper

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You proabaly couldn't win this case in a court of law, but it sure seems very likely that you are on the right track.

Reply to
hrhofmann

Since the tact switches are N.O. you can easily prove them to be contaminated. They plug directly into the MPU as does the IR-RX.

I have been on house calls of heavy smokers. Everything is covered with tar. I too smoke, maybe 6 or 7 cigs a day. I own two Hunter QuietFlo

30736 tower air purifiers that are on here 24/7. Really keeps the dust down and no sign of any tar. Your theory is solid. And easy to confirm. 
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Live Fast, Die Young and Leave a Pretty Corpse
Reply to
Meat Plow

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I found a thick film of yellow,brownish sticky residue on the board. Dust sticking on the HV wires and yoke looked like feathers. I have to move these sets out of the shop and blow them out with the vacuum before I can even work on them. I replaced all the switches on this one and cleaned the control board with 99% isopropyl . The problem seems to have abated. Qtips were completely brown, sadly, probably the same color as his lungs. Thanks for listening. Lenny

Reply to
klem kedidelhopper

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