Sony Trinitron KV32FV27 Power Supply Problem

[cmonkey]

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.

[R_J]

Your meter is likely a pos. it can't handle the high switching frequency that is on those mosfets, What is the make and model of your meter?

[cmonkey]

Your meter is likely a pos. it can't handle the high switching frequency that is on those mosfets, What is the make and model of your meter?

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 and tested.

All the RED highlights are bad voltage readings.

[cmonkey]

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?

[cmonkey]

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?

[cmonkey]

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.

[cmonkey]

I have no continuity between pin 1 and pin 3 on T501, which doesn't seem right. Registers about 100 ohms.

[cmonkey]

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.

B -> E = .03v
B -> C = .45v

E -> B = .03v
E -> C = .45v

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, however the ohm reading between B and E is 60 ohm.

Part number is - 8-729-045-26 2SD2580-YB

[petehall347]

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.

B -> E = .03v
B -> C = .45v

E -> B = .03v
E -> C = .45v

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, however the ohm reading between B and E is 60 ohm.

Part number is - 8-729-045-26 2SD2580-YB

..there you go

[cmonkey]

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.

[petehall347]

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.

check out the datasheet picture showing the diode and resistor inside it .

[cmonkey]

check out the datasheet picture showing the diode and resistor inside it .

Dang, so these readings look alright then. Thanks for pointing that out.

[cmonkey]

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 main AC plug coming in, I get 120v AC on pin 2, but on pin 1 when I measure in AC mode it beeps and the numbers just go nuts. When on DC it settles on 163VDC.

Edit - I'm actually getting 163VDC from CN602 all the way to the main bridge rectifier D602 on both rails. Rail 1 also test 120VAC and rail 2 beeps a lot and just flashes numbers.

My ground is on the negative pin of D502.


Is a defect that makes this reading even possible or is my meter on the fritz?

[petehall347]

I'

My ground is on the negative pin of D502.

i might be missing something but why choose that point for ground reference ?

[cmonkey]

i might be missing something but why choose that point for ground reference ?

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."

[cmonkey]

You need to know the difference between the HOT (primary side) of the power supply, and the COLD (chassis) side. They are marked on the board and the two sides are separated by a white line. When checking voltages on the HOT side you MUST use the negative pin of the bridge rectifier for your meter negative probe. You can not use chassis ground when checking primary voltages.

Should I be using that negative pin on D502 as a ground when checking the AC voltages behind the bridge rectifier?

[cmonkey]

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.

[cmonkey]

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 there's no voltage my DMM jumps around a lot in the millivolt range, but not on this one, it jumps right to 240 millivolt and stops.

Not sure what else to do at this point so if anyone has any pointers I'd be very grateful.

[R_J]

I traced the line all the way back to IC001 and there's no voltage on pin 16 at all

microprocessors do not operate without Vcc voltage

[cmonkey]

microprocessors do not operate without Vcc voltage

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?