Chimei DAC-19M009 Power Supply problems

[shane_newcastle]

Re: Chimei DAC-19M009 Power Supply problems

hello all this is my first post here and im sorry top revive an old thread but i thought it best seeing as though i have issues with this exact power supply

First of all,with the power supply plugged in (to both the monitor and AC power) CAREFULLY measure the voltage across the two pins of the large cap. I've circled them in red in the attached picture. This point packs enough of a punch to give you a jolt.

If you get either 150-170 VDC or 300-340 VDC the next step is to disconnect AC power from the board and unsolder 1 lead of the fuse circled in blue. Hook the board up again and see if the power LED works properly now.

If you still get nothing, it is time to take a picture of the area I have circled in green. Photograph both sides of the board. I am looking for any information on what voltages to expect.

PlainBill

im getting 350vdc at the cap tried unsoldering the fuse no change
in the area in blue there is a 13.8v out put which is reading 14.29v
but the 2 outputs marked 5v are reading nothing
any help in this matter would be greatly appreciated

[PlainBill]

Re: Chimei DAC-19M009 Power Supply problems

The bridge rectifier was blown, so I stuck in one taken from an old PC PSU, changed the fuse again, and gave it a try and it all seems to work OK. Now the gamble is to stick with it as is and assume an outside surge blew the rectifier, or to keep exploring, and risk damaging the board with my pretty basic soldering/desoldering techniques. Thanks for helping me get to a working monitor.

You're welcome.

Assuming you replaced the the fuse with one of correct value, there is no reason not to use the monitor. The most likely cause for the bridge shorting was a voltage spike. The second most likely cause would be excessive current.

PlainBill

[caryg]

Re: Chimei DAC-19M009 Power Supply problems

The bridge rectifier was blown, so I stuck in one taken from an old PC PSU, changed the fuse again, and gave it a try and it all seems to work OK. Now the gamble is to stick with it as is and assume an outside surge blew the rectifier, or to keep exploring, and risk damaging the board with my pretty basic soldering/desoldering techniques. Thanks for helping me get to a working monitor.

[PlainBill]

Re: Chimei DAC-19M009 Power Supply problems

OK, it's not just a power surge that popped the fuse; I stuck another in there and that went the moment I plugged it in. Does that suggest that the faulty component is likely to be close-by? I'm not too sure where to look next. I had hoped that the dud fuse suggested that those FETs were really OK. Would they cause the main fuse to blow? Thanks for the help so far. I would never have realised that the little black box squeezed in under the power cable was a fuse. Is it normal to make them so inaccessible?

Well, the days where a fuse was a user-replaceable part are long gone. In part, this was because users would figure that "if a 3 amp fuse blows, let's try a 15 amp."

There are several possibilities. The likely culprits are the bridge rectifier, the switching transistor driving the transformer, and the transformer itself. I'd suggest pulling each of them and testing with a DMM.

PlainBill

[caryg]

Re: Chimei DAC-19M009 Power Supply problems

OK, it's not just a power surge that popped the fuse; I stuck another in there and that went the moment I plugged it in. Does that suggest that the faulty component is likely to be close-by? I'm not too sure where to look next. I had hoped that the dud fuse suggested that those FETs were really OK. Would they cause the main fuse to blow? Thanks for the help so far. I would never have realised that the little black box squeezed in under the power cable was a fuse. Is it normal to make them so inaccessible?

[caryg]

Re: Chimei DAC-19M009 Power Supply problems

First of all,with the power supply plugged in (to both the monitor and AC power) CAREFULLY measure the voltage across the two pins of the large cap. I've circled them in red in the attached picture. This point packs enough of a punch to give you a jolt.

PlainBill

The big cap gives me nothing at all, which suggests that something on the mains side has gone. Looking closer I see that underneath the wire earthing the board to the mains socket there is a fuse marked T3.15A 250V CQ and under that MST JET. A fuse which has blown. Bearing in mind the clean state of the rest of the board I'm tempted to find a replacement and see what happens. Now I just have to get at the awkward little fellow.

[caryg]

Re: Chimei DAC-19M009 Power Supply problems

Check those FETs they are the drivers for the inverter transformer think of them as the HOT of the LCD world they fail and fail often .

OK, Assuming that the dot on the top of the FET marks pin1, and that they then run 1,2,3,4 up to the top then 5,6,7,8 down the other side, and according to the datasheet the pins are (from 1 to 8) S2, G2, S1, G1, D2, D2, D1, D1, then I get the following readings, pretty much identical on both FETs, according to which way round I have the DMM leads (Red/Black)

S1 Red to G1 805
S1 Black to G1 787
S1 Black to D1 663 (both pins)

S2 Red to G2 330
S2 Red to D2 614 (both pins)

Everything else gives no reading. S1/G1/D1 and S2/G2/P2 seem to be wired up in reverse, so I would expect them to conduct in opposite directions. I would guess that I shouldn't be getting the first reading listed, the S1 Red to G1, and therefore both FETs have blown. The fact that the S2 circuit reads only half the value (and I'm not sure what exactly I'm measuring here) would confirm it. It looks odd that they have both apparently blown the same way. Is this common, or am I mistaking something?

Thanks for the pointer to the FETs; now to hunt down a supplier.

[PlainBill]

Re: Chimei DAC-19M009 Power Supply problems

D'oh! I was making such a hash of trying to upload a photo that I missed that bit out. It's completely dead, no sign of life at all, not even a blinking LED.

First of all,with the power supply plugged in (to both the monitor and AC power) CAREFULLY measure the voltage across the two pins of the large cap. I've circled them in red in the attached picture. This point packs enough of a punch to give you a jolt.

If you get either 150-170 VDC or 300-340 VDC the next step is to disconnect AC power from the board and unsolder 1 lead of the fuse circled in blue. Hook the board up again and see if the power LED works properly now.

If you still get nothing, it is time to take a picture of the area I have circled in green. Photograph both sides of the board. I am looking for any information on what voltages to expect.

PlainBill

[Krankshaft]

Re: Chimei DAC-19M009 Power Supply problems

Check those FETs they are the drivers for the inverter transformer think of them as the HOT of the LCD world they fail and fail often .

If they've been replaced once already I'd check for cracked solder joints in the inverter area. No need to deal with a repeat failure.

http://www.alldatasheet.com/datashee...D/AOP605L.html

To test DMM to diode check from source to gate reverse probes should only read in one direction from drain to gate same applies. There are two in one package. If you read a short then the IC is shot.

[caryg]

Re: Chimei DAC-19M009 Power Supply problems

D'oh! I was making such a hash of trying to upload a photo that I missed that bit out. It's completely dead, no sign of life at all, not even a blinking LED.

[PlainBill]

Re: Chimei DAC-19M009 Power Supply problems

I've got a 22" Chimei branded monitor which seems to be fairly similar to the Westinghouse 19" which already has a long thread here, but instead of the 19M005 power board it's got one marked 19M009, and rather infuriatingly it looks like they've replaced the troublesome MOSFETs on that board with something marked P605 BD7C1F. Does anyone here have any experience with this board and any hints on where to look. The caps all look OK, and both the glass fuse on top and the little one underneath test fine. Here's a photo which may help

What problem are you having?

PlainBill

[caryg]

I've got a 22" Chimei branded monitor which seems to be fairly similar to the Westinghouse 19" which already has a long thread here, but instead of the 19M005 power board it's got one marked 19M009, and rather infuriatingly it looks like they've replaced the troublesome MOSFETs on that board with something marked P605 BD7C1F. Does anyone here have any experience with this board and any hints on where to look. The caps all look OK, and both the glass fuse on top and the little one underneath test fine. Here's a photo which may help