On Sat, 11 Sep 2010 18:25:59 -0700, klem kedidelhopper wrote:

On Sep 11, 2:56Â*pm, Meat Plow wrote:
On Sat, 11 Sep 2010 11:45:29 -0700, klem kedidelhopper wrote:
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 Â*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

Unplug the IR receiver and tact switches ( P/J3001)then retest.

--
Live Fast, Die Young and Leave a Pretty Corpse- Hide quoted text -

- Show quoted text -

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 a "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


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.


--
Live Fast, Die Young and Leave a Pretty Corpse