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chumba
Joined: 01 Jul 2009
Posts: 66
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 Posted: Sat Oct 24, 2009 9:29 pm Post subject: |
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Replaced IC803 and the TV is now powering on!! YES! 
However a new problem showed up - none of the power or control buttons function with the buttons themselves or the remote. 
When the TV is plugged in it powers directly on with no user intervention.
When each control button is pressed (such as Volume, Channel, Video, etc), every button instead triggers like the ACTION button was pressed. There were no shorts measured across all pins of Q001. |
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JTS1957
Joined: 21 Jan 2009
Posts: 1331
Location: Far, Far Away
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| Posted: Sun Oct 25, 2009 12:09 pm Post subject: |
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Remove "Action" switch / check for shorts, etc.  |
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chumba
Joined: 01 Jul 2009
Posts: 66
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| Posted: Tue Oct 27, 2009 7:23 pm Post subject: |
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Removed ACTION switch S008 and IR receiver IC003 and measured no shorts on either part out of circuit nor on PCB lands. Other panel switches measured ok - normally open, and short when pressed. Left S008 and IC003 out of circuit and same problem still occurs (will not power off with switch).
Now the 1st time the TV is plugged it does NOT power on by itself and WILL power on with the switch, but will then not power off.
I am suspecting there may be a problem with Q001 connecting to the PCB since it is a tiny surface mount - what other components should each leg connect to? I want to check continuity out from E, B, & C of Q001. |
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chumba
Joined: 01 Jul 2009
Posts: 66
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| Posted: Thu Oct 29, 2009 6:25 pm Post subject: |
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Now TV will not power on and no relay clicks at all
I think I may have inadvertently touched 2 pins of Q001 together with the meter and the TV then shut off for good. Main fuse is still good but I dont measure any low or high DC Voltages. What should I check? |
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JTS1957
Joined: 21 Jan 2009
Posts: 1331
Location: Far, Far Away
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| Posted: Thu Oct 29, 2009 11:08 pm Post subject: |
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Grind the tips of you meter's leads to a very sharp needle point, that should keep them from slipping off inadvertently.
Microprocessor "may" be at fault...
"Action" switch feeds to one pin of the microprocessor (pin 6); Rest of front panel switches form a voltage divider network and feeds a different microprocessor pin (pin 5). Remote receiver should feed into microprocessor on pin 1.
Pin #61 is 5 volts (VDD) - Pin 22 is 5 volts (AVDD) - Pin # 31 is power On/Off to the base of Q001 - pins 62/63 are 12Mhz oscillator - Pin 59 & 60 are SDA/SCL respectively (should have 3.7 volts - and activity on a scope when any front panel switch is pressed). |
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chumba
Joined: 01 Jul 2009
Posts: 66
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| Posted: Fri Oct 30, 2009 9:44 pm Post subject: |
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| Not getting any DC voltages on any pins of IC803 nothing on any pins of HOT, and no B+ @ C806. Only measure 4.9v / 2.3v / 0v on Q001, and nothing on that microprocessor. |
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JTS1957
Joined: 21 Jan 2009
Posts: 1331
Location: Far, Far Away
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| Posted: Sun Nov 01, 2009 2:50 pm Post subject: |
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D802 cathode/C805 "+"/ IC803 pin #3 to HOT ground reference (C806 negative terminal) = ~300VDC?
Stand-by supplies D001 cathode to COLD ground reference (Tuner shield) = ~12VDC?
Q002 Emitter to COLD ground = ~5VDC? |
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satyrias
Joined: 29 Oct 2009
Posts: 61
Location: Houston, TX
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| Posted: Sun Nov 01, 2009 4:02 pm Post subject: |
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Please excuse me for interjecting with my question here. I am a novice and a basic question.
I am also dealing with a Pan CT27SF31 TV and trying to trace the problem. When you measure the voltage of the components, what are the test points need to use? This model also has the same IC803. Would you tell me how did you measure it? I have a multimeter where do I place the leads?
Also What is COLD or HOT ground means? |
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JTS1957
Joined: 21 Jan 2009
Posts: 1331
Location: Far, Far Away
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| Posted: Sun Nov 01, 2009 9:42 pm Post subject: |
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As I previously stated earlier in this same thread:
| JTS1957 wrote: | This chassis uses a HOT ground for the power supply and horizontal deflection areas of the set.
COLD ground for everything else. |
When all sets used a power transformer in their power supply, the AC line voltage was transformer coupled by separate (isolated) windings. Sets today do NOT usually use such a transformer.
Most components on the AC side (HOT side) of todays SMPS transformers (switched mode power supply) reference the same point that one side of the AC cord attaches to. Usually called Hot ground.
Most components on the DC side (COLD side) of this same transformer use a "common" point as reference or ground. Hence common or cold ground. |
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satyrias
Joined: 29 Oct 2009
Posts: 61
Location: Houston, TX
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| Posted: Mon Nov 02, 2009 2:41 am Post subject: |
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JTS1957 Thank you very much.
I have another thread next to this with CT2731S. Would you help me there since I don't want to disturb this thread with my problem. I am trying to trace the circuit step by step. |
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