Home |
Search |
Today's Posts |
|
Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
|
|||
|
|||
CTC185AA3 startup problem
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. |
#2
|
|||
|
|||
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. 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. |
#3
|
|||
|
|||
|
#4
|
|||
|
|||
I can almost guarantee it is conductive glue under that capacitor in the
reset circuit. David |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Problem with new water heater (electric) - please advice | Home Repair | |||
Boiler Problem Gradually Getting Worse | UK diy | |||
High voltage problem with JVC AV27BP4 TV | Electronics Repair | |||
CRT Contrast Problem | Electronics Repair |