Samsung HTP5044 power supply or main board

[DavidOH]

I've had this set for some time now. It would not power on. I changed somethings on the PS with no luck. I read that some sets have an internal test pattern. Tried it didn't work. When I plug it in nothing happens. SM test said bad main board. I've now discovered that if I short pin1(PS_ON)and pin5(GND_18V AMP) on connector CN801 on the PS. It will come on and operate normally. So which board is could be causing the problem? Was going to get a main for it but thought I'd post here first. I could solder a jumper on those pins. But I don't think that would be a good idea. I can get pics tomorrow if needed. Thanks

http://assets.shopjimmy.com/media/ca...bn9401517a.jpg

http://assets.shopjimmy.com/media/ca...bn4400162a.jpg

[budm]

Re: Samsung HTP5044 power supply or main board

The PS_ON is generated by the main board. PS_ON is usually >3vdc = ON.

[Fix My Plasma]

Re: Samsung HTP5044 power supply or main board

I would 100% say Power Supply.

Shockingly common fault.

[tom66]

Re: Samsung HTP5044 power supply or main board

If PSU comes on when PS_ON jumpered, it's not the power supply... unless it's missing some other voltages like Vs/Va.

[DavidOH]

Re: Samsung HTP5044 power supply or main board

Vs/Va are ok. The PS in sending 5V to the main on pin2. But not getting 5V back on pin3. I'm taking a close look at the main. Lots of surface mount components.

[DavidOH]

Re: Samsung HTP5044 power supply or main board

Well now it will power up but no picture. Manual test still says bad main board. It's the only reason I can think that would let work one time and not the next. Unless it's in the logic board. I'll figure it out.

[tw2005]

Re: Samsung HTP5044 power supply or main board

Well now it will power up but no picture. Manual test still says bad main board. It's the only reason I can think that would let work one time and not the next. Unless it's in the logic board. I'll figure it out.

Before you get a main, pull the ymain and test the 88n30w fets for shorts as it's common for these to go together with a shorted upper buffer board

[DavidOH]

Re: Samsung HTP5044 power supply or main board

I've checked the voltages while powered on. I'm missing the Ve. Instead of 94v I'm getting 4v. The cap near the test point 25v220uf reads .41. What should I start checking?

[DavidOH]

Re: Samsung HTP5044 power supply or main board

The caps check good. I'm going to start checking the diodes along that side next.

[ben7]

Re: Samsung HTP5044 power supply or main board

Common fault with this PSU is one or both of the MOSFETs on the middle heatsink (skinny one, in the center of the board) going bad. Our samsung has the same PSU, and it had a problem where it wouldn't power up (kept clicking). Two of the MOSFETs were bad.

Replace the two 1000uF 25v capacitors just below the inductors LX804 and LX803. Also replace CX814 and CX813. These all had bulged slightly on mine, but wasn't the direct cause of the problem.

[DavidOH]

Re: Samsung HTP5044 power supply or main board

I've replaced all four of the mosfets and the two caps at CX813/14. I just checked the esr of the four caps next to LX803/4. The two 25v1000uf are .12 and the two 35v470uf are .04. I've pulled one leg of the three big diodes near the four caps. I'm not sure of the readings. I'm getting 308,146 and 158 on the diode test. These are bottom of the board above CN801.

[awyatt2]

Re: Samsung HTP5044 power supply or main board

david have you checked esr on the startup caps? i had one of these sets a while back and the problem was not the power supply it was the ymain it would work at times and not at other times. does the ve try to come up or steady 4 v? if it tries to come up i would look at the ysus if not then it is probally ps related

[DavidOH]

Re: Samsung HTP5044 power supply or main board

I haven't checked it that way. I've only checked after the power is on. I'll check it next time. I haven't checked the three big caps. But have checked most of the smaller ones. I'm going to finish checking them while it's out this time.

[awyatt2]

Re: Samsung HTP5044 power supply or main board

startup cap is one of the smaller caps 10uf if i remember correctly. it is near a 8 leg ic

[DavidOH]

Re: Samsung HTP5044 power supply or main board

Okay I'm going to check the rest of the caps tonight.

[DavidOH]

Re: Samsung HTP5044 power supply or main board

I checked the rest of the caps. They all check OK near as I can tell. I'm still getting the hang of this Blue esr meter. I also took a reading during power up for the 94v. No spike, just a steady climb to 4v. Guess I can start ckecking some of the resistors in that section and the mosfets on that side. Think I'll look the service manual over again first.

[awyatt2]

Re: Samsung HTP5044 power supply or main board

there are a couple of diodes that are three leg to220 case mounted on a heatsink look like a transistor they sometimes fail on samsungs. have you tested them? check for shorts and opens with ohm meter. they usually have a diagram on the device showing common cathode, common anode or back to back. we are watching a 55 sammy that i bought for 50.00 and it was just one of the diodes open. luck and merry christmas. i just finished up a th50px60u panasonic i am thinking of giving my daughter tomorrow.also just to mention this as a precaution if you use the esr on in circuit caps it will read the entire string of caps if parallel or series. in this case you need to remove one leg to test for sure. had a polaroid and it all checked out ok until i realized this fact. one bad cap and it tested good till i started dropping one leg.

[DavidOH]

Re: Samsung HTP5044 power supply or main board

If you look at the 3 pics above I removed the semiconductor on the right. It is connected to the Ve pin on
CN809. I think it is bad but not sure if I'm testing it right. The part number is KIA7815API. The datasheet has pin1-input, pin2-gnd, pin3-output.
In diode test with negitive on gnd I get nothing on input and output. With postive on gnd I get 578 on input and 678 on output.

On 20k ohm there is nothing between 1-2,1-3, and 10.26 between 2-3. Which test is right and is this shorted like I think it is? Or am I just way off.

[awyatt2]

Re: Samsung HTP5044 power supply or main board

7815 is a voltage reg 15v pos. input should be a couple of volts higher than 15 and output should be 15 volsts with the ps on. you should be able to find it at radio shack. i have always tested them by output voltage it is not a transistor it is an intergrated circuit.the center is common look up the data sheet for the input and output pins.

[DavidOH]

Re: Samsung HTP5044 power supply or main board

I'd already look at the data sheet. But after I read your post the input/output hit me. I looked at the SM and the Ve 94v I'm looking for isn't coming from the PS. It comes from the x-main to the PS. Guess I should have ckecked the SM sooner.