Samsung PS42C450B1W sound no picture

[llonen]

Re: Samsung PS42C450B1W sound no picture

I could do with some input on this before I return another set of boards, currently three blinks from red panel led, the green led on the control board is displaying one long flash. I have not been able to locate any obvious defective components on either the xsus or ysus boards.

Vsc is around -140 volts which is still low as per panel spec and Ve 75 volts

Have tried the set with xmain removed and no image and or priming, power supply goes into protection mode, and I don't get a Ve measurement.

Have tried the set with Y scan buffers removed and the power supply still goes protection mode, vsc 140 volts.

[llonen]

Re: Samsung PS42C450B1W sound no picture

Yet another x sus board and Y sus board later (thankfully did not have to pay for replacements) I am still no closer to a repair solution with this set. I may well end up scrapping this set as irreparable as I have wasted to much time on it already.

I have had six sets come through and go back out in the time I have had this one in the workshop.

[ReeceyBurger123]

Re: Samsung PS42C450B1W sound no picture

Wait wait wait, have you tested the buffers for S/C first ?

[llonen]

Re: Samsung PS42C450B1W sound no picture

I did test the Y buffer panel for shorts and found nothing that appeared shorted, that does not mean it does not have shorts just that the 5 volt or there about's that my fluke test kit generates may not be sufficient to find it.

Set history to date

Came in with shorted xsus mosfets, it was likely this was caused by an unstable power supply, psu was reworked and a number of bad solder joints remade. Board tested as good, Xsus board tested as non shorted.

Then while under test psu went into protect mode and no picture or prime (sound and main board responsive). re examined Xsus board and Y sus board no obvious shorts found. Tested Ybuffer board no obvious faults found.

Ordered and replaced Xsus and Y sus with known good boards, returned one faulty Xsus board (board was tested and identified as bad before fitting) and fitted replacement second Xsus. Sound no picture psu going into protect mode and VSC appeared low and VE seemed unstable.

Replaced second set of Xsus and Y sus boards no change, I normally have a good success rate or repairing X and Ysus boards.

I put in a rebuilt psu panel from spares, simply because I had one in and no change.

The Ybuffer board is about the only board I have not changed to date, although removing it from the Ysus made no difference.

[flocko]

Re: Samsung PS42C450B1W sound no picture

Doing a search for this set and the Bush BPDP42 Will tell you that the best way to repair this model is to replace the Ysus/Xsus and Y buffers as a set,it is one of those models that any bad board will damage the rest, so failing to test any replacement board will result in you going round and round blowing more and more boards. so check all board for damage(shorts) before powering on.

[llonen]

Re: Samsung PS42C450B1W sound no picture

I have tested the boards for shorted rails and devices, and I have checked replacement boards upon receipt for shorted rails and devices before installation and power. I am going to replace the Y buffer board only because I have located a 'tested' cheap one and the only reason I am going to do this because there is nothing I can find wrong with the existing ybuffer panel is simply that is the only board I have not replaced twice now.

thoughts to date are

1 Five defective boards, actually six if you count the Xsus board I repaired defective boards

2 There is some anomalous problem on the Ybuffer panel that has not shown up. in spite of the set actually working for a while after the first board repair.

3 I have received thus far three xsus boards (one was found faulty) two Ysus boards all with the same resultant fault.


if this does not resolve the problem and I am guessing it wont, the thing is going to tv heaven unless some one can suggest something I have missed.

With today's workload completed that will have been 10 sets repaired (two plasma) and various items that have come through in the time I have wasted on this.

[ReeceyBurger123]

Re: Samsung PS42C450B1W sound no picture

What sort of condition is the set in ? I might consider buying it, I like the image on these when they are working save trashing it.

[flocko]

Re: Samsung PS42C450B1W sound no picture

How are you testing the buffers +Sus board ?If you read the posts that i have told you to, you will see that any bad board (shorted)will blow any good boards you fit, this applies to a lot sets . It is no good throwing boards at a set without checking they are good boards, being told there good by a seller does not mean a thing, checking is down to you before fitting.I test and then put void tape over the sockets any Sus or buffer boards I sell for this reason, and will not except any shorted board returns that the void tape has been removed.

[llonen]

Re: Samsung PS42C450B1W sound no picture

Buffer panel was tested first at the input feeds from the Ysus board to pcb ground reference, with panel disconnected from Ysus and pdp, the channels tested individually to ground reference. discreet components were then tested, nothing of significance found. Ysus board(s) were tested for ve and vs to ground shorts, then the individual IGB mosfet's were tested in circuit for shorts, diodes also tested for shorts. Capacitors of significance were tested (not ESR).

Xsus board(s) were tested for VS and VE short to ground reference, individual IGB mosfets were checked for shorts along with the diodes, discreet components were checked. Other than the initial failed Xusu board which I replaced the IGB mosfets on and one replacement board which was returned to seller with a VS short and shorted IGB's nothing else of significance was found. (not ESR)

Any board that has been ordered has been tested as per the above description, if you think I have missed anything out, please let me know.

Test equipment used

Fluke 77
fluke 79 series 2 (for component checks)

Old meters but they serve me well
I have oscilloscopes available

I think the cost of shipping this to you would be prohibitive, otherwise the condition is good and there were no pdp panel faults on this set when it did briefly work.

[flocko]

Re: Samsung PS42C450B1W sound no picture

Well your testing skills needs a little work, i will give you5/10. I would recommend you spend some time searching the forum for testing advice, start with buffer testing,then move on to Sus and power boards. It has all been covered, you just need to search as I have been telling you.We are here to help but you must also help yourself

[llonen]

Re: Samsung PS42C450B1W sound no picture

Thanks for the rating, most of the tests recommended have been carried out, with the results. I have been repairing a very wide range of electronics and electrical appliances for the last 8 years, including plasma televisions this amounts to hundreds of items each year, very occasionally I have need to refer a repair to forums.

Currently the thinking points to a short on either the XSus or Ysus boards, presumably the same short that is on five boards four of which are claimed good (ok lets now go there).

The problem being that the short(s) are not showing up, please feel free to let me know what I have missed. I don't have a ESR meter, and to be honest I don't like most of the ones current to market but do feel free to recommend a good one though. Instead I use the component test built into one of several test meters, and if i need to test a capacitor further then I use a function generator and oscilloscope.

I could remove the major semi conductors from the Xsus and Ysus boards and test them to the data sheets, very time consuming and I am not convinced this would show up anything useful as the devices do not seem shorted in circuit. It would show up any that had failed open though (which I understand is rare), the decision to replace with 'good boards' was an economical one, as the cost of parts to rebuild Ysus board seemed prohibitively expensive and with no clear starting point it would be a case of replacing all of the IGB's and diodes on each board.

Anyway do let me know what I have missed.

[flocko]

Re: Samsung PS42C450B1W sound no picture

The advice I am giving to you ,is use the forum search, saying you have tried most of recommended tests, why only most, if you were to search the model as i have told you, you will see you are falling into a common trap, going round and round replacing board after board. without the right testing of all three boards and knowing they are good, you will be unable to get off the merry go round.

[llonen]

Re: Samsung PS42C450B1W sound no picture

Well, having sent back three defective boards to date now to various Ebay suppliers, that leaves me with two Ysus boards one original to the set (status unknown) two Xsus boards one original (repaired) to the set (status unknown) and one ybuffer board (status unknown). Ordered replacement Ybuffer / ysus and Xsus boards as despite retesting each board as per various threads and professional articles to the limits of the test equipment I have available I cannot confirm which are faulty and or what those faults maybe.

Boards arrived, test and inspection prior to fitting reveal, wait for it

One faulty Y buffer set (shorted to ground channels), a faulty Ysus (bad IGB's) and faulty Xsus (Bad Igb's), and these boards are being sent from a supplier that claims to test and only send working boards.

Thankfully other than my wasted time this has not really cost me anything to date as each board returned has been refunded with postage costs.

Anyone want the sellers name I will happily send it to them via Im

[flocko]

Re: Samsung PS42C450B1W sound no picture

This is what happens if a buyer or seller do not know how to test . you put what you are told is a good board in with your known good boards , and you end up with your once good board now being blown. as long as you test buffers for output shorts to the ICs ( test in low ohms. floating ground to panel ribbons sockets) and Y+ X board (test in low ohms all supply to common ground + each other) you should be good to go . not hard , just remember a short is a low resistance between two points and should be tested as such (meter set to low ohms ) the use of diode mode is for test diodes and transistor that are removed from circuit the testing of IGBTs can be done on board (low ohm) or to fully check operation in diode mode out of circuit, as long as your meter has the output voltage to turn the device on

[llonen]

Re: Samsung PS42C450B1W sound no picture

Nods, and thus the problem, I currently have one reworked Xsus board that had two bad IGB's, these were changed by by myself and the board retested, it appears clear of shorted devices, and neither the Vs or Ve rails show as shorted to board ground. I have a Ysus board (original) that I suspect has a fault on it (only can't the fault). I have Ybuffer board (original) that is clear of output shorts to board ground, and is clear of shorted input rails to board ground.

Any boards that I order are tested prior to installing, and the faulty ones have to date been returned. this leaves me with an additional Ysus board and Xsus board that seem faulty (faults not found) The seller has refunded me the monies spent on these.

And of course the last set of boards that have now been sent back as supplied faulty, ybuffer, Ysus and Xsus.

The test meters I use (fluke77 and fluke 79) certainly found the defective devices on the replacement boards ordered from various sellers.

Now according to the service manual for the fluke 77 diode test has a test voltage of 2.4 volts.

I could take the components out of circuit and test on a current limited bench supply, I have the relevant solder extrator equipment to do this painlessly.

Or I could try sourcing another set of 'tested' boards and see what I get this time.

By the way I have had five various televisions, including one plasma come through the workshop this week.

[flocko]

Re: Samsung PS42C450B1W sound no picture

Buffers boards need to be tested to floating ground, not board ground (common ) using common ground will not show any defective ICs. Insulated Gate Bipolar Transistors will in most cases fail short, and should be tested with a meter set to low ohms , to find any (gate /emitter/collector) shorts.
A meter with 2.4vtest voltage set in diode mode, is to low to turn on most IGBTs

[elviramjw]

Re: Samsung PS42C450B1W sound no picture

my U5000 has no middle. blown out. dont know what part number it is.
any one know and where i can buy one from

[elviramjw]

Re: Samsung PS42C450B1W sound no picture

update, 2 transistors and one diode all short circuit.
Y-Main pcb LJ41-08592A rev 1.3 (LJ92-01737A)

D5007 - UD1006
Q5003 and its neighbour RJP30E2
U5000 - UM7510 Digital Isolator

replacements on order.