37pd5200e smps

[zx81]

Hi Guys,

I wonder if you could assist me repairing a SMPS ?

I have attached some pictures of the board which is from a Hitachi 37PD5200E.

I replaced r003 and r005 both where open circuit but r003 failed again after the relays clicked for just a second. Main fuse before the supply board was and still is fine.

I'm thinking that the Mosfets pictured may be the cause but I'm worried about damaging the surge protection resistor again.

The main problem is I am not sure if the daughter board and what I think is the driver IC201 could also be short? My dilemma is I don't know how to test this IC for shorts or other faults and it has loads of SMD components on it.

I may have also jumped the gun a bit in assuming that the main filter caps and bridge rectifier where fine as the main fuse looked ok.
Caps looked fine visually too. No bulging or oozing electrolyte.

I will be removing the Mosfets, large filter capacitors, bridge rectifier from the board and test out of circuit.

Just not sure what to do to test the driver ic201 without access to an oscilloscope ?

Could I use a 100watt bulb across the fuse holder (with the fuse removed) after I have replaced any parts that are found to be faulty? Will this protect the board and the surge protection resistors and any other components from damage ?

[zx81]

Re: 37pd5200e smps

Sorry Guys,

I should have put in the manufacture name in the title of the thread along with model number. Tried editing my thread but wasn't able update the title to show on the top page.

Cheeers,

zx81

[paulstef]

Re: 37pd5200e smps

Does this diagram make sense?

[zx81]

Re:Hitachi 37pd5200e smps

Does this diagram make sense?

Hi Paul,

Thank you for your reply.

Yes it makes sort of sense its a kind of block diagram of the stages of the SMPS.

I'm pretty much a beginner in electronics and I can kind of follow it through.

This is what I understand and please feel free to correct me if i'm wrong.

On the left of the diagram I see the AC comes in IC202 needs to see STB 5v
also checks if the PFC is ok along with other voltage checks. If all is okay then the AC detect stage turns on the relays RL002 and RL001 very confused on this section

The bridge rectifier does a full sine wave rectification of the AC.
Then we move to PFC section which I think is the power factor correction stage which involves IC001, transistors Q003/4/005.
I don't totally understand how the PFC section works but it involves AC100v,320v AC200v,370v not 100% sure what this all is but I understand it is used to make the power output more efficient and reduces power consumption.

The large capacitors C201 and C016 filter the DC power and send DC via diode D020 and D021 to Capacitor C101 which in turn goes to STB transformer T101. IC101 then somehow goes on to provide STB 5v and a regulator is also used off T101 to have a regulated stepped down STB 3.3v

T201 is for 30v, 12v,10v and 5.1v IC201 as I understand it is the driver which controls the on off state and time for Mosfet Q201 (this is the section I am not sure how to test without scopes and knowing the pin outs. I'm worried that if there is a short here I might not be able to fix it. I suspect Q201 may be faulty but will have to remove it and test. Could Q201 have been damaged by a fault IC201?

Then there is T301 Va (60v) and Transformer T501 Vs (80v)
I'm not sure what IC391 does. I think its somehow involved with the HV output section. But I can see the chopper is somehow involved with IC391 and the HV output section.

I hope you'll forgive my noob interpretation of these things. I only started learning about SMPS yesterday and as you can see I have a lot to learn

zx81.

[zx81]

Re: 37pd5200e smps

I should have mentioned I could just go and replace parts by taking them out of circuit and testing for faults. But I am a Knowledge Seeker and would like to learn as much as I can about the circuits I'm working on. Hopefully in the distant future I may try and build my own circuits just for fun.

zx81

[paulstef]

Re: 37pd5200e smps

page 7 of the diagram I posted shows the AC input circuitry. The relay RL002 should short the inrush current limiting resistors once the main caps are charged.

In your first post you said Resistor r003 failed again after the relay clicked once. Do you mean RLY001?

Without the signals PFCGO,VCEGO, VSAGO there shouldn't be excessive current draw initially.
Disconnect from AC, (always make sure main caps are discharged!)
Q003 and Q004, make a diode check from drain to source (middle and right pin). should read open. Then inverse the probes, should read a diode drop.

Is the board disconnected from everything else apart AC mains?

[zx81]

Re: 37pd5200e smps

Yes Paul I can definitely confirm r003 is open circuit r005 is reading 10ohms it lasted a few seconds i heard the relays click followed by a hiss of power. I thought it was going to be okay but r003 went went open again.

I had it working for about 3 seconds

[zx81]

Re: 37pd5200e smps

Also did my peanut sized brain interpret 10% of whats going on in the circuit as per my post no:4 ?

[paulstef]

Re: 37pd5200e smps

You don't need to understand in detail the whole circuit right away.

What's with Q003 Q004?

[zx81]

Re: 37pd5200e smps

Not managed to find Q003 or Q004 I think they may be hiding under one of the heatsinks. They should be in the vicinity of IC001 and the bridge rectifier. I'll take another look for them.

This board has documented issues with the Mosfets Q220 Q201 both K2843's but I can't find those parts in stock locally. I think they've been discontinued so may need to source an alternative also r003 and r005 are quite commonly faulty from what I've read.

Will start taking bits out and testing. Will revert back when I've done more tests.

Cheers,

zx81

[zx81]

Re: 37pd5200e smps

I now have the parts and will be looking to replace them this weekend.

Could any of you guys please suggest a way to determining if the driver IC (pics attached) is not shorted before I go ahead and replace the K2843 mosfet and 5watt 10ohm resistor? I'd like to avoid damaging the new parts if at all possible.

Would the 100watt bulb across the main fuse help in this instance?

[zx81]

Re: 37pd5200e smps

Any help or advice would be much appreciated.

[multimeter]

Re: 37pd5200e smps

I now have the parts and will be looking to replace them this weekend.

Could any of you guys please suggest a way to determining if the driver IC (pics attached) is not shorted before I go ahead and replace the K2843 mosfet and 5watt 10ohm resistor? I'd like to avoid damaging the new parts if at all possible.

Would the 100watt bulb across the main fuse help in this instance?

driver ic's that i have seen always go short VCC to ground pin,check the datasheet to determine the pins.

yes, use the light bulb across the fuse holder,it will limit the current and avoid more damage,a dim lightbulb is a good sign,if it stays bright,there is still a short in the primary section

[paulstef]

Re: 37pd5200e smps

Nothing looks damaged on IC201. There are not a lot of components on this board. I would at least diode check the diodes/transistors but that's about it.

A light bulb instead of the fuse would limit the current in case of a short, yes. If it stays lit once the main caps are charged and there is no load on the PS output (standby) there is a problem.

[zx81]

Re: 37pd5200e smps

Thanks for your replies guys.

I feel a little more confident now and will try and replace the the faulty components.

[zx81]

Re: 37pd5200e smps

A quick update.

I have now replaced R003 which was open circuit and a K2843 MOSFET which was shorted.

When I fired up the set with a 150watt bulb in place of the main fuse the bulb goes from off to very bright within half a second or so the relays click and then after a short time this whole process cycles again and again.

I'm not sure what to make of this result does this mean I still have a short somewhere else in the primary side?

The good thing is that non of the replaced or other components blew using the light bulb.

Any guidance on how to proceed and what to check next would be very much appreciated.

[paulstef]

Re: 37pd5200e smps

A 240V/150W lamp has about 380 Ohm at 150W. (cold it's much lower). That means you have 380 Ohm in series with the rest of the circuit. Something in the circuit has a much lower equivalent resistance than 380Ohm.

1. Which relay clicks?

2. Can you measure the coil voltage of RL002 (DC) to see if it ever gets a signal (initially)? For R003 to burn (without the light bulb) the relay RL002 must be open.

3. What's the output voltage at the bridge rectifier when the light bulb is fully on?

4. Is the rest of the TV PCBs connected or are you working with just the PSU?

5. What is the AC line voltage? What is the voltage on the light bulb?

[zx81]

Re: 37pd5200e smps

Paul I can answer questions

4) All other PCB where connected.

5) Line voltage is 240v the bulb is also 240v

I will test and get back to you re 1,2 and 3

I purchased this set faulty from EBay specifically to help me learn about fault finding and learning more about SMPS and TV's in general. I'm in no real rush to fix or sell it. I sometimes have long gaps before I can carry out tests due to work. So please bear with me. It's just a hobby but I'm very eager to learn as much as I can. SMPS seem very complicated to me as a beginner but If I can learn how these things work and how to identify and diagnose faults it should be a very valuable experience.

Paul your helpful guidance is really appreciated.

zx81

[zx81]

Re: 37pd5200e smps

So far I've replaced R003 (5watt 10ohm) and Q201 (K2843) Mosfet. Tried the bulb across the fuse holder and the bulb went out. So I proceeded to replace the fuse and fire up the set. Unfortunately there were a few sparks followed by a bang Main fuse blown R003 open again Q201 blown again.

I've removed the daughter board IC201 which is the driver for the damaged Mosfet. Also attaching some scans of the IC components. I'm trying to check for shorts as best as I can. Not sure how I would test the capacitors marked in red in the scan?

I'm also unsure how to test voltages when the set is plugged in do use Hot or cold ground ?

Any tips on how to proceed would be appreciated.

Thanks in advance.

[paulstef]

Re: 37pd5200e smps

Not sure how I would test the capacitors marked in red in the scan?

I'm also unsure how to test voltages when the set is plugged in do use Hot or cold ground ?

They are not necessarily capacitors, could be inductors too, but less likely. Truly testing them requires them to be removed and measured. They are unlikely to have lost capacitance. they could be short though.
There are diodes too (black , 2 pins) and transistors. One would need to draw the diagram to be sure what is what.

If you turn the set on and then Q201 blows up then it's because its gate is driven ON. PC201 is open as long as the secondary voltage 5V (page 96) is lower than 5V. So the IC201 does not seem to activate OUT1 which would turn off Q201. It stays on, T201 saturates and boom. Overcurrent.

You measure all voltages to their respective ground (if that's what you want to do). Everything that is between AC IN and one of the SMPS transformers is live and measured to hot ground. Everything after the SMPS transformers is measured to cold ground. Then there can be more SMPS following these, not necessarily in this TV though.

Don't get confused. There can be many more than just two grounds or references in a circuit. References can also be positive. What the reference is for a certain part of a circuit depends on the circuit.


What you need to understand and repair this is:
- draw at least part of the circuit of IC 201
- an oscilloscope
- an isolation transformer

You can also try to at least check shorts in power semiconductors to start with. But then you will need to do some serious troubleshooting.