I have a hunch about why IC001 has died. I was thinking about when I did the B+ voltage test with the lightbulb. The B+ line was sitting at about 45v when on, but when I flipped it off it would surge up to about 65v or 70v for some reason. The bulb got significantly brighter.
I noticed the same thing with the 5v standby line when I was trying to figure out what was causing the power to flick off and on. The voltage went up to about 7v each time it turned off.
I looked in the data sheet for IC001 and it's rated up to 5.5v for the Vcc in and so maybe that surge up to 7v...
cmonkey
Senior Member
Last Activity: 12-10-2024, 08:36 AM
Joined: 04-28-2023
Location: USA
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No there is no light at all on the front. No voltage of any kind has been fed into the TV other than via the main connector.
That being said, the past day or two I've been having an issue with the power in this TV flicking on and off ( the relay clicking over and over again ), quite rapidly sometimes and I didn't figure it out until tonight, because I went back to test the two 5v pins on IC001 and there no voltage there. There must be a loose/weird connection in the cable going from A board to G board, because when I was wiggling it the 5v was going on and off the IC001.
...Leave a comment:
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So I just remeasured and pin 62 actually has 27 millivolts on it.Leave a comment:
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Sorry I had my pins swapped. Pin 62 (pwron) has no voltage and pin 16 (standby) has 4.84v.
Isn't the microprocessor generating the 3.5V pwron voltage?...Leave a comment:
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Well things have turned worse, I don't have PWRON voltage at all now. I traced the line all the way back to IC001 and there's no voltage on pin 16 at all. R070 tests fine and I can't find any short to ground anywhere on the PWRON circuit, including around Q652 and Q653.
Pin 62 of IC001 has 4.84v from the standby line.
Continuity between components seems good, I can't find any broken traces.
The only weird reading I can find is that Q648 has 5v at it's collector but then I'm getting about 240 millivolt on the base of Q648 which stops at D614. Normally when...Leave a comment:
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So I've hooked up a lightbulb in circuit on the B+ line of this TV and have disconnected the B+ line on the main board and the B+ voltage has dropped to about 45v from 60v, so this is definitely a power supply issue.Leave a comment:
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Should I be using that negative pin on D502 as a ground when checking the AC voltages behind the bridge rectifier?...Leave a comment:
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First page, R_J - "When checking voltages on the HOT side you MUST use the negative pin of the bridge rectifier for your meter negative probe."...Leave a comment:
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I've done quite a lot more testing this week and have not found any issue at all on any component on directly on the B+ line around all of the horizontal drive components on the main board. I attached a photo of what I tested.
I also reflowed all the joints on the flyback, Q501, Q502, T501 and T502.
I've gone back to the power board and have noticed something different when testing on the HOT side of the board. For some reason I'm getting DC readings where I'm pretty sure I should be getting AC readings.
The most obvious is when testing CN602, which is the...Leave a comment:
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Dang, so these readings look alright then. Thanks for pointing that out....Leave a comment:
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Ok thanks, so it is an NPN and these readings are bad.
I still need to test all the components adjacent to the HOT to make sure none of those caused this to fail.Leave a comment:
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Not sure but I might have found my first bad part. I took the HOT (Q502) out of circuit and it's not measuring right from what I can tell.
I think it's an NPN transistor and I'm getting the following voltage drops. Red ones seem wrong, unless this isn't an NPN.
[COLOR=#e74c3c]B -> E = .03v[/COLOR]
B -> C = .45v
[COLOR=#e74c3c]E -> B = .03v
E -> C = .45v[/COLOR]
C -> B = 0v
C -> E = 0v
Can anyone clarify if this is the correct way to test this transistor?
None of the diodes is shorted,...Leave a comment:
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I have no continuity between pin 1 and pin 3 on T501, which doesn't seem right. Registers about 100 ohms.Leave a comment:
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Slight bit of progress, I found a loose connection on C624 which was causing the recent issue with the 0V across the entire cold side of the power supply. When I replaced it I guess the pad lifted slightly.
I tried disconnecting one leg of R652 to sever the B+ voltage line from the power board to the main board, but that resulted in 0V across the entire cold side of the power supply except for the PWRON which sat at 0.7V and the standby at 5V. The B+ voltage must allow for the power supply to switch on, so my next step is to start stepping down that rail on the main board.Leave a comment:
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One other thing I just noticed/remembered while looking through my notes, the Ground pin on IC641 is reading 0.5V when it should be reading 0. The adjacent pin on D647 is also reading 0.5V and beyond the diode it's all 0V.
Would this suggest that IC641 has shorted internally?...Leave a comment:
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So I've been thinking about IC643 DM-58 Power Control IC and wondering how does this IC work? I cannot find a datasheet for it.
IC641 (9v regulator) and IC650 (12v regulator) would output bad voltages if they are not getting a correct input voltage am I right?Leave a comment:
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Its a Mastech MS8268. I do remember briefly getting readings on IC601 when the set turned on once and the voltages were correct based on the schematic, so I'm pretty sure it can read the voltages correctly.
I figure I should post a screenshot of the PDF I've been making notes in, I'm still not convinced that this is not a power supply board issue given how many voltage points are wrong across it.
Everything on the bottom of the G board schematic that generates the 5V standby tested fine.
All the GREEN highlights are components that I removed...Leave a comment:
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The voltages on IC601 are all wrong as well. I'm testing it in DC with the negative probe on the negative pin of D602 and get the following -
B2 - 185V
C2 - 330V
E2 - 188V
The positive pin of D602 is also reading 330VDC.
Also, my multimeter starts squealing when I test B2 and E2.Leave a comment:
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I just don't know what to make of this. I let it sit for an hour and now it's behaving like before I left it sit for a few months.
The relay clicks again and I have bad voltages all over the secondary side.
These two are correct -
PWRON - 3.6v
Standby - 4.97v
These are all wrong -
12v rail - 3.8v
9v rail - 1.06v
B+ rail - 57V (should be 135V)...Leave a comment:
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So I've picked this up again, however, now the TV has does absolutely nothing when I turn it on. Not even any clicks.
I started testing the HOT side voltages, and there is no power going to the bridge rectifier. I made it back to one of the relays and found that RY600 has the 5v on the cold side, but it's not tripping on the hot side, only one of the legs of the relay has 120V.
Problem is, I can't even find this relay anywhere if I wanted to try replacing it.
Does anyone have any tricks for finding old parts, or finding a new replacement?
The...Leave a comment:
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