Help with Bentek DMC BP-200AD Power Supply

[grzesiek]

Re: Help with Bentek DMC BP-200AD Power Supply

Although I always warn people when they are about to take dangerous high voltage measurements, I do often forget to tell them to put on safety glasses. Sorry about that, I really hope you're okay.

No need to appologize. I always take basic safety precautions when working on most anything. You need not feel responsible for not stating the obvious.

we can trick the power supply to "think" that the standby section is okay - if you have spare chargers and adapters, that is).

Do you mean stuff like wall chargers and adapters for other devices? If so, Yes. If not could you be more spicific?

Any chance you know what C22 was rated for? It's not necessary, but would be interesting to know. Hopefully there are enough remains of that capacitor to determine that. If not, what are the part numbers on IC3?

Attached are pictures of the casing of the C22 Capacitor, as well as one of IC3. So no problem with Identification, but the part number of IC3 is 5M0365R.

I'll get on the next set of tests you described now.

[momaka]

Re: Help with Bentek DMC BP-200AD Power Supply

I desoldered R22. Not sure what happened, but when I put the meter probes on pins at CN2, the Capacitor at c22 exploded. After catching my breath, testing the pins, I'm now at 1.25VDC.

Although I always warn people when they are about to take dangerous high voltage measurements, I do often forget to tell them to put on safety glasses. Sorry about that, I really hope you're okay.

Removing R22 would indeed raise the voltage across C22, but I didn't think it would be (and it really shouldn't be) anywhere near that high to make it explode.

I think this may be the reason why the FAN7527B APFC controller died too.... perhaps the supply voltage went over 30V and killed the FAN7527B IC. Any chance you know what C22 was rated for? It's not necessary, but would be interesting to know. Hopefully there are enough remains of that capacitor to determine that. If not, what are the part numbers on IC3?

With that cap blown, I guess that means no more "live" voltage measurements for now... at least not without a 40-60W incandescent light bulb wired in series with the power supply's input - that way, if something does go wrong in the power supply, at least you won't have a ton of components exploding at you.

Overall, it looks like the "body count" will be high with this power supply. If you would like to continue, then the next step would be to troubleshoot the PFC section (even though the standby clearly has a problem, we can leave that for later because we can trick the power supply to "think" that the standby section is okay - if you have spare chargers and adapters, that is).

Starting with Q6, which is obviously bad, you can desolder it from the board (this time no explosions, I promise ). Also remove Q5 and R55 - they should be okay but the reason to remove them is to isolate the FAN7527B IC by itself so we can do measurements on it.

Next, check the following diodes near FAN7527B IC: D4, D5, D15, and D16. To check those diodes, use the diode test function of your multimeter. When reading the diode forward-biased (i.e. red multimeter probe on anode and black multimeter probe on cathode), you should get a reading between 200 mV and 1000 mV (or 0.200V and 1V). When reading the diode reverse-biased (i.e. multimeter probes backwards of forward-biased), ideally you should get no reading (though that won't always be the case with in-circuit readings. If in doubt, remove diode and test out of the board. In any case, you should never get beeping on continuity across a diode or 0 mV or 0V when the diode is removed from the board. If you do, then you have a bad diode. Post what results you get for those diodes above.

Finally check the following resistors: RS1/RS2, R2, R3, R5, R6, R7, R8, and R9.
For these, basically read the resistor's color code (or Google an application that can do that for you - though it's very easy) then check the resistance of that resistor with your multimeter. In circuit, you should get either the same or lower resistance than what the resistor's color code indicates, but never higher (within about 5%, that is). Also, note for RS1 and RS2 - these are very low resistance resistors (0.24 Ohms each), so your multimeter likely won't be able to measure them properly in circuit. You will need to remove these from the board and check them. It appears as if one has a burn mark on it, so it may be blown. Check.

I didn't find D2. There is a D7 in that area, is that what you ment, or did I just miss it?

D7 it is. The picture was convincing my eyes that it was a "2" at first, though. Regardless, it wouldn't have made a difference whether you removed that or R22 like you did.

Both joints apear solid.

Okay.
Reason I asked is because there was a slight burn mark on the under side of the PCB in that area and the joint looked a little damaged on one end.

168.9 - 170.0 VDC

Supply voltage is okay too.

The power supply in the TV I repaired, also Bentek, had significant discolouration on the board.

I figured out the problem. The power consumption in standby is 15W; and almost all of this goes into the PSU, across a few load resistors and the startup resistors. It also has no standby mode. The main outputs are always running and the inverter is just turned off in standby using the on/off signal, it still receives 24V continuously.

Wow, that is a horrible design then. Does yours have a standby transformer, though? Because this one does and I think the main outputs are disabled when the TV is "OFF". Also, by any chance does your power supply have a FAN7527B APFC controller? Could be useful to us to determine that R10 resistor.

[grzesiek]

Re: Help with Bentek DMC BP-200AD Power Supply

Not good.

Try removing (desoldering) either D2 or R22. They are both in that darkened section of the power supply (the standby power circuit).
Then see if you get 5V on connector CN2

I desoldered R22. Not sure what happened, but when I put the meter probes on pins at CN2, the Capacitor at c22 exploded. After catching my breath, testing the pins, I'm now at 1.25VDC.

I didn't find D2. There is a D7 in that area, is that what you ment, or did I just miss it?

check the solder joints on D8 and R23

Both joints apear solid.

Also check the voltage across C52

168.9 - 170.0 VDC

[tom66]

Re: Help with Bentek DMC BP-200AD Power Supply

The power supply in the TV I repaired, also Bentek, had significant discolouration on the board.

I figured out the problem. The power consumption in standby is 15W; and almost all of this goes into the PSU, across a few load resistors and the startup resistors. It also has no standby mode. The main outputs are always running and the inverter is just turned off in standby using the on/off signal, it still receives 24V continuously.

Crazy, that's 80's VCR, not 00's LCD TV!!

[momaka]

Re: Help with Bentek DMC BP-200AD Power Supply

I'm only getting 3.25VDC.

Not good.

Try removing (desoldering) either D2 or R22. They are both in that darkened section of the power supply (the standby power circuit). This will disable power going to the FAN7526B controller (the FAN7527 APFC controller and the standby PWM-FET, IC3, share the same auxiliary winding on the standby transformer to get their power). Then see if you get 5V on connector CN2. If you still get the same 3.25 VDC, check the solder joints on D8 and R23 (again, found in the darkened area in the standby section near the standby transformer). Also check the voltage across C52 and report back. Like the big brown cap, this cap should also have about 160-170V across it, so again, BE CAREFUL when you measure there.

It's been a year, but I replaced the Capacitor there, and as I recall the discoloration was there then. This will be the 4th time this board has been worked on (twice by MFG), I did that Capacitor.

Ouch. One heck of bad design then. I was also working on a TV power supply today that had a toasty standby section. It was a very different power supply, but has similar specs to yours.

[momaka]

Re: Help with Bentek DMC BP-200AD Power Supply

I just noticed... Q6, a small TO-92 transistor next to the FAN7527B APFC controller is also more than likely bad since a piece of it is blown away. Not that it matters too much at this point, but I'm just noting this down for myself here in case I forget I saw that. With Q6 bad, chances are either the FAN7527B APFC controller and/or the APFC MOSFET Q1 are bad too. But we will get to that.

**EDIT**
Just saw your post above. Give me a few minutes to type a response...

[grzesiek]

Re: Help with Bentek DMC BP-200AD Power Supply

Next, with the power supply plugged in, see if you get 5V on some of the pins of connector CN2 (the middle one on the output side of the power supply).

I'm only getting 3.25VDC.

The PCB in that section of your power supply seems to have darkened quite a bit.

It's been a year, but I replaced the Capacitor there, and as I recall the discoloration was there then. This will be the 4th time this board has been worked on (twice by MFG), I did that Capacitor.

[momaka]

Re: Help with Bentek DMC BP-200AD Power Supply

My reading varies a bit, but the 450V Capacitor is 169VDC (168.5 - 169.2)

Good.
That eliminates a big chunk of work.

Next, with the power supply plugged in, see if you get 5V on some of the pins of connector CN2 (the middle one on the output side of the power supply). Most (if not all) of the time, these power supplies with APFC will not work unless the stand-by power circuit is working. The PCB in that section of your power supply seems to have darkened quite a bit.

[grzesiek]

Re: Help with Bentek DMC BP-200AD Power Supply

Also, is your multimeter auto-ranging or manual-ranging?

The meter is a GB Instruments GDT-11. Manual Ranging.

Yes, a multimeter is more than enough for now. However, a soldering iron and solder will also become necessary sooner rather than later, especially if you have to remove components from the board to test/replace them. You don't really need a fancy soldering iron. 35 to 45W will do the job (although if you do have something better, that's always good). You may also want to get flux - both liquid and paste is fine, but I prefer paste since it doesn't dry and is easier to apply.

I have all that... 45 watt soldering iron, solder, paste flux.

However, to keep things simple, first check the voltage across that big brown 450V cap on the primary side. To do that, you will need to have the power supply plugged in to the wall (though not necessarily connected to the rest of the TV). Since the APFC circuit isn't working, you should get only about 160-170 V DC across that cap. If not, let me know.

My reading varies a bit, but the 450V Capacitor is 169VDC (168.5 - 169.2)

[momaka]

Re: Help with Bentek DMC BP-200AD Power Supply

So if you are still willing to help, you may have to be more detailed than you are used to.

I do have a multimeter (ACV, DCV, AC Amp, and Continuity). I am familiar with its use, but this will be far more technical than I have utilized it for.

I've seen quite a few newbies here start with almost no knowledge of how to use a multimeter and then after a week or so were okay with it. So I have no doubt you will be okay with all of this. I just hope you don't mind my long posts.
Most of the time, we will be using the DCV, continuity/diode test function, and resistance measurement. The only thing I ask is that when you report numbers from the multimeter, take careful note of the units and their prefixes.
(if not familiar with the prefixes, see this:
http://en.wikipedia.org/wiki/Metric_prefix)
Also, is your multimeter auto-ranging or manual-ranging?

Is this sufficient for this project? If not what will I need? I'll get it.

Yes, a multimeter is more than enough for now. However, a soldering iron and solder will also become necessary sooner rather than later, especially if you have to remove components from the board to test/replace them. You don't really need a fancy soldering iron. 35 to 45W will do the job (although if you do have something better, that's always good). You may also want to get flux - both liquid and paste is fine, but I prefer paste since it doesn't dry and is easier to apply.

Would this mean that the Resistor would/could be un-necessary?

Well, I'm sure the designers of this PSU put it there for a reason so it probably isn't unnecessary. However, the fact that the sample APFC circuit (page 9 on that URL) doesn't have one means that the value of that resistor can likely be "ball-parked".

The Line voltage is 110V (house current 220V Split Phase). So I suspect I won’t be able to disable the Active Power Factor Control.

There is a way, but the mod is not very "neat". So I'll leave that for if all other methods fail.

So, if my ignorance has not made you reconsider, How should I proceed?

You'll have to try harder to make me reconsider

With component failures on the primary (high voltage) side, I always start by checking the input section components first (with the power supply unplugged). However, to keep things simple, first check the voltage across that big brown 450V cap on the primary side. To do that, you will need to have the power supply plugged in to the wall (though not necessarily connected to the rest of the TV). Since the APFC circuit isn't working, you should get only about 160-170 V DC across that cap. If not, let me know.
Be careful, though - THIS IS THE HIGH VOLTAGE SIDE OF THE POWER SUPPLY. AVOID TOUCHING ANY COMPONENTS WITH YOUR BARE FINGERS! EVEN THE HEAT SINKS ARE ENERGIZED!
Also, when testing the power supply, make sure you do so on a non-metal and non-conductive surface. (I'm sure you know this already, but in case anyone else is reading that doesn't know. I saw a fellow tech once try to test a motherboard on a metal counter top and was wondering why it wouldn't power on. )

[selldoor]

Re: Help with Bentek DMC BP-200AD Power Supply

If you gave up in the future this guy seems to do a board repair - He is in Canada so you could say you cant afford repair plus shipping and be cheeky and ask him what value the resistor has - you may strike lucky. As it is his business I doubt if he will tell but you never know.
http://nickwillfixit.com/BP200AD%20specs.htm

Perhaps you could update your profile with country and mains voltage

[grzesiek]

Re: Help with Bentek DMC BP-200AD Power Supply

momaka... Thanks so much.

If you want to troubleshoot your power supply, you will need a multimeter and some knowledge of how to use it, so let me know if you want to go that route instead.

I would like to try to fix this board. If for no other reason, than to say I did. In the name of 'Full Disclosure' I have very limited experience with electronics repair. So if you are still willing to help, you may have to be more detailed than you are used to.

I do have a multimeter (ACV, DCV, AC Amp, and Continuity). I am familiar with its use, but this will be far more technical than I have utilized it for. Is this sufficient for this project? If not what will I need? I'll get it.

I also looked up a sample APFC circuit for the FAN7527B controller, and the resistor that burned in your power supply was actually omitted from the sample circuit design and instead pin 4 of the FAN7527 controller was directly connected to the sensing resistor.

Would this mean that the Resistor would/could be un-necessary?

By the way, what's your line voltage? If 220/230/240 VAC, then another possible option is to disable/remove the APFC circuit and then fool the power supply that the APFC is working.

The Line voltage is 110V (house current 220V Split Phase). So I suspect I won't be able to disable the Active Power Factor Control.

So, if my ignorance has not made you reconsider, How should I proceed?

Mike

[momaka]

Re: Help with Bentek DMC BP-200AD Power Supply

But it did get me wondering... if there is another TV manufacture that used a board with the same specifications that could be made to work.

Yes, most of the time that is do-able. Actually, the only specs you really need to be concerned about are the output voltage rails and the currents they can supply. i.e.:
5 Vdc at 4.0A
12 Vdc at 4.0A
24 Vdc at 5.5A

So basically, if you can find a power supply that has 5V, 12V, and 24V, and the currents on each of these rails is the same or higher than the ones on your power supply, then you might be able to use that power supply. And I say *might* because some power supplies may require some modifications to make them run with your TV. But judging by your power supply, that may be fairly easy - you just have to make sure the wire for the power supply ON/OFF control is connected to the proper ON/OFF control pin on the new power supply. Most of the time, they are compatible (i.e. the TV's main board brings the ON/OFF control pin to 5V and the power supply outputs are turned ON).

But anyways, all of that above is if you want to make a different power supply work. Personally, I like to try to fix the original power supply first if parts are reasonably cheap.

Aside from that blown resistor R10, MOSFET Q1, sense resistors RS1 and RS2, and the APFC controller IC1 (FAN7527B) may also be bad. If you want to troubleshoot your power supply, you will need a multimeter and some knowledge of how to use it, so let me know if you want to go that route instead.

I also looked up a sample APFC circuit for the FAN7527B controller, and the resistor that burned in your power supply was actually omitted from the sample circuit design and instead pin 4 of the FAN7527 controller was directly connected to the sensing resistors. Given the nature of the way your resistor blew, though, I'm almost certain your FAN7527B controller is bad too. But again, we can only confirm that with a multimeter.

By the way, what's your line voltage? If 220/230/240 VAC, then another possible option is to disable/remove the APFC circuit and then fool the power supply that the APFC is working.

[grzesiek]

Re: Help with Bentek DMC BP-200AD Power Supply

Still trying to research a fix for this TV. I noticed on ebay there are a LOT of tv power supplies for sale. Of course none for mine. But it did get me wondering... if there is another TV manufacture that used a board with the same specifications that could be made to work.

Here are the Specs of the BP-200AD.

Input Voltage
- Normal Voltage : AC 100-240 Vrms
- Voltage Range : AC 90-264 Vrms
Input Frequency
- Normal Frequency : 50-60 Hz
- Frequency Range : 47-63 Hz
Input Current
- <3.0 Amps at 90 Vac Input
- <1.5 Amps at 260 Vac Input
Inrush Current : <80 A at 230 Vac
Earth Leakage Current : 0.5mA MAX. at 240 Vac

Output Requirement:
Output Voltage/Current
- + 5Vdc /4.0A Tolerance(5%)
- +12Vdc /4.0A Tolerance(5%)
- +24Vdc /5.5A Tolerance(5%)
Ripple & Noise
- + 5Vdc : 50-150mVp-p
- +12Vdc : 120-300mVp-p
- +24Vdc : 200-300mVp-p
Efficiency
- >75% at 90-264Vac input (Maximum Load Condition)

Anyone have any thoughts suguestions?

[grzesiek]

Re: Help with Bentek DMC BP-200AD Power Supply

momaka,

Thanks. I'd be willing to try a ghetto fix, That's better than no fix.

I've attached a few more Pics... Is there any thing in paticular you need to see?

The Upload seems to be compressing them, I can RAR them if you like.

[momaka]

Re: Help with Bentek DMC BP-200AD Power Supply

^ You don't have to toss the TV just because the power supply isn't working.
Lots of "ghetto" ways to rig in a power supply to power the TV. Or you can also sell it for parts.

With more clear pictures of both side of the board, though, I think we may have a shot at fixing this power supply.

[grzesiek]

Re: Help with Bentek DMC BP-200AD Power Supply

Tom,

I'd hate to toss this TV. Would you have any suguestions as to what to do?

[tom66]

Re: Help with Bentek DMC BP-200AD Power Supply

I have worked on a similar PSU. It's in the kitchen in the student dorm currently, as it was very cheap.

This is a very poor quality PSU (as was the one I worked on) and likely a MOSFET has failed short on the power supply which has destroyed that resistor.

[grzesiek]

Re: Help with Bentek DMC BP-200AD Power Supply

Tom,

Thanks for the reply. I've attached a couple shots. One of the board as a whole, and 2 of the affected area. I think you'll agree that there was something there.You can (barely) see the stubs of the legs.

[tom66]

Re: Help with Bentek DMC BP-200AD Power Supply

Can you share a picture?

It is possible the component is not meant to be there. Sometimes components aren't placed for some versions or to lower the cost.