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CTC185AA3 startup problem

L

Lenny

Jan 1, 1970
0
I have been working on this set on and off for the past few weeks. I
kind of put it on the back burner for awhile though and just got back
to it. This was one that sometimes would not start up. John Del had
suggested checking the 5V reset voltage,(which would probably read
low), and then measuring the resistance on the reset pin of the UP
while heating nearby caps one by one with the soldering iron and
looking for a change. When the resistance dropped sharply that cap was
most likely the bad one.
I attached a couple of wires to pin 2, (reset), and ground measured
200K ohms. I plugged the set in and the voltage was 2.3 volts. The
high resistance suggested no loading or dead short so I tried turning
the set on and surprisingly it went on normally. I ran it for a few
minutes and shut it down and some time later it would not come back
on. I checked the voltage and resistance again and they were still
2.3V and around 200K resectivly.
I disconnected power and tried heating the caps while watching the ohm
meter and there was no change. I plugged the set back in and while
monitoring the 2.3 V I briefly cold sprayed the area of pin 2 on the
foil side of the board. The voltage abruptly dropped to zero and the
resistace dropped to 40K. I powered down and waited a few minutes and
the resistance eventually came back to 200K but when the set was
plugged back in the voltage remained at zero. Naturally the set will
not come on now. And now I have no voltage on pin 2 but still measure
200K.
I don't really know where the 2.3V went. So since there didn't appear
to be a short to ground on pin 2 I decided to try applying 5V to pin 2
and attempt turn on. The set came on, stayed on as long as 5V was
present and quit as soon as I removed the 5V.
I have no schematic and feel like I'll probably need one to chase this
further unless someone has some ideas. I'd really like to see this set
leave. Thanks for any help. Lenny Stein, Barlen Electronics.
 
R

RonKZ650

Jan 1, 1970
0
Is your 5v supply normal on pin 21? If it's low trace back to Q3901 5v
regulator and U4102 12v regulator to see if you've got correct voltage. Either
way, this is the area you need to be looking, the 12v output of U4102 goes to
Q3901 to make the 5v source, but also spits off to Q3102 then Q3101 then off to
your pin 2 reset through a few resistors ect, which should be at 5v normally.
 
M

Master TV

Jan 1, 1970
0
I have been working on this set on and off for the past few weeks. I
kind of put it on the back burner for awhile though and just got back
to it. This was one that sometimes would not start up. John Del had
suggested checking the 5V reset voltage,(which would probably read
low), and then measuring the resistance on the reset pin of the UP
while heating nearby caps one by one with the soldering iron and
looking for a change. When the resistance dropped sharply that cap was
most likely the bad one.
I attached a couple of wires to pin 2, (reset), and ground measured
200K ohms. I plugged the set in and the voltage was 2.3 volts. The
high resistance suggested no loading or dead short so I tried turning
the set on and surprisingly it went on normally. I ran it for a few
minutes and shut it down and some time later it would not come back
on. I checked the voltage and resistance again and they were still
2.3V and around 200K resectivly.
I disconnected power and tried heating the caps while watching the ohm
meter and there was no change. I plugged the set back in and while
monitoring the 2.3 V I briefly cold sprayed the area of pin 2 on the
foil side of the board. The voltage abruptly dropped to zero and the
resistace dropped to 40K. I powered down and waited a few minutes and
the resistance eventually came back to 200K but when the set was
plugged back in the voltage remained at zero. Naturally the set will
not come on now. And now I have no voltage on pin 2 but still measure
200K.
I don't really know where the 2.3V went. So since there didn't appear
to be a short to ground on pin 2 I decided to try applying 5V to pin 2
and attempt turn on. The set came on, stayed on as long as 5V was
present and quit as soon as I removed the 5V.
I have no schematic and feel like I'll probably need one to chase this
further unless someone has some ideas. I'd really like to see this set
leave. Thanks for any help. Lenny Stein, Barlen Electronics.

You might want to try removing smd c3126 and cleaning glue underneath
and than reinstall....
 
D

dkuhajda

Jan 1, 1970
0
I can almost guarantee it is conductive glue under that capacitor in the
reset circuit.

David
 
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