Philips 40PFL3505D/F7 Blows fuse when plugged in

[Mad Capper]

Philips 40PFL3505D/F7

Serial YA3A

Found this and did not turn on when plugged in so I opened it up and found it had a bad fuse so I replace and it blew the fuse again immediately when it gets plugged in.

I read: https://www.badcaps.net/forum/showthread.php?t=24655 and that was resolved with a new PSU.

I did these procedures using these images as reference:
https://www.badcaps.net/forum/showpo...1&postcount=46
https://www.badcaps.net/forum/showpo...7&postcount=52
https://www.badcaps.net/forum/showpo...2&postcount=53

Board Info here: Pages 10-3,4,5 and 10-17
http://www.scribd.com/doc/80791100/40PFL3705D-F7


It had D1202 and R1609 bad and they were replaced along with new C1602 and SA1601 just to be safe. Put in a new fuse and plugged it in and instantly blew the fuse again. Now D1203 and D1203 come up bad. In the above mentioned thread https://www.badcaps.net/forum/showpo...&postcount=169 someone mentions D1208, a zener diode, as the cause for their fuses continuing to blow.

I do not know if blowing 2 diodes is a sign of progress or not. Why would another one fail?


I tested the zener diode D1208 according to http://www.learningaboutelectronics....-a-zener-diode

and it gets about 1.8ohms in both directions which seems to point to it being shorted. Is there another way I should be testing the zener diode with a meter to see if it is indeed bad?



The zener diode is a 1M200Z:


I can get a NTE5104A, 190V locally, would that be an acceptable substitute or does it need to be 200V.


Would replacing D1202 and D1203 and D1208 fix this problem? What else could be causing this problem and what else should I check? Is one persons mention of a bad zener diode a red herring?

Should I again replace the SA1601, R1609 and C1602 or are they probably still good and if I do not will that cause the same or another problem down the line?

Thank You for your time and any assistance you can provide in fixing this TV.

[Agent24]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

Which fuse is blowing?

[Mad Capper]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

The main ceramic fuse F1601, T8AH250V

[selldoor]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

You can save all these new parts from blowing by using a 75w filament bulb in series with the positive power input look up "Dim Bulb Test"
We might spot something if you post good clear pictures of your boards

[Mad Capper]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

Here are pictures of the front and back of the power supply board. Please excuse the diodes at D1201-D1204 I pulled up to check and the missing zener diode at D1208.

[Agent24]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

If D1208 shows 1.8 ohms both ways that does sound bad, likely it's shorted.

A 190v zener might work but it all depends on the circuit. At a lower voltage you are unlikely to cause damage to anything, but it may clamp the voltage too low and cause improper operation of the circuit.

I would try to get a 200v zener unless anyone can confirm otherwise


After replacing the zener and the other diodes, use the lightbulb test as selldoor said so you don't blow them again if there is still a fault.

[Mad Capper]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

Is there anything else I should be testing or looking for that could be the potential problem?

If 190v is not good what about a 200V 1.5W or greater wattage rather than 1W spec for the zener diode?

Thanks

[selldoor]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

If it has been worked on before check anything on heatsinks has insulation shims if required.

[Agent24]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

If 190v is not good what about a 200V 1.5W or greater wattage rather than 1W spec for the zener diode?

I can't imagine it would be an issue to go with a higher wattage.

That said I do recall reading somewhere that higher wattage zeners may have a slower recovery time, whether this is even true or will have any bearing here I don't know.

[budm]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

That Zener D1208 is the protection if the AC line voltage goes above 140VAC, normally at 120VAC you will have about 169~170VDC apllied to that Zener, but if the AC line Voltage goes up to 140VAC, the dc Voltage will be about 200VDC which will be clamped by the Zener abd if it went way beyond that then the fusible resistor R1201 will go open, this Zener is there to protect the standby power supply section which on 24/7 so it will see all the surge and spike on from the power line all the time. You can use higher Wattage as long as it will fit the foot print. R1201 is OK?

[Mad Capper]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

I have read the following posts that reference this power supply board and tried to do some more testing, thus the long post.
https://www.badcaps.net/forum/showth...erson+lc407em1

https://www.badcaps.net/forum/showth...rson+lc401em2f


BudM, As far as I can tell R1201 checks out good. From what you said is it possible that the zener is bad but not the resistor?

Either way I still get low ohms both ways on the zener.

selldoor, It has not been worked on before and all components on heat sinks have their thermal paste intact.



Should I be testing any or all of the transitors to see if there is a bad one? As I get easily confused please clarify something for me if you could. When looking at a datasheet for transitors I have a few basic questions.

First is it supposed to be the view looking down at the transistor with the legs pointing toward you or looking at the top of the transistor?

Second to identify their ECB, Some transistors physically look like image 1 and some like image 2 as seen in the attached image.

My question is, for both the ones with a rounded side or a chamfered side, is the flat side always the flat side, therefore disregarding whether it is rounded or chamfered, i.e. no matter if the datasheet image physically looks like the acutal transistor would making the flat sides match while looking at it in the correct orientation give me the correct ECB location?

I ask this because I had gotten confused because while starting to test the transistors With Q1404, TRANSISTOR KTC3199-GR-AT/P, it is a rounded one and has printed on it 5343 Y043 so that in itself did not make sense to me. Looking at the datasheet: for it it does not show it having a rounded side, thus my above questions.



Next. Trying to see what else I should be looking at I came across this.

According to Flow Chart 1 page 8-1 of the service manual, disregarding the fact that my fuse still blows, it is possible that IC 1201 and T1201 are bad and is there a way to test them?

I think it is possible that both the zener D1208 or the IC1201 is bad because they are parts that the shopjimmy.com rebuild kit references as potential items to replace due to the fuse blowing.


Printed on the board is BA01P0F0103 3 and the sticker says A01PNMPW. Crossreferencing with tv models and board numbers seem to indicate that the rebuild kit would be for my board if I choose to go that route.

http://www.shopjimmy.com/magnavox-a1...repair-kit.htm
http://www.shopjimmy.com/p-f-a01pemp...a-rebuild.htm#



I tested the mosfets Q601, Q1702, Q1701, Q1602, Q1602 accorinding to the 4 steps here: http://www.sentex.ca/~mec1995/gadgets/mostest.htm

All worked as the test describes except Q601. If I touch the positive lead to the gate then to the drain I get open, if I hold it on the gate for a few seconds then move to the drain it flashes a number then goes open. I assume this means it is bad, correct? Is my testing method correct? If so are there other components that I should check.

Having read more from other threads concerning this power supply and how the troubleshooting went I next tried the 'light bulb as fuse' technique. The parts that were removed, or in the case of some diodes a leg lifted, were IC1201, D1201-D1204, D1208, Q601, Q1404, Q1402, Q1706. Using first a 60W bulb then a 100W bulb across the fuse and plugging the tv into the wall the light bulb stays off. In the end it seems it is the zener D1208 for a majority of people. That being said if my above test of the mosfet Q601 was done correctly, does it being bad make you think of any other components that could also be bad?


If I read correctly this means that for what is left attached to the board there are no shorts as the light bulb is not on, correct? And I should repeat the bulb test method after reinserting the above mentioned components one at a time, correct?

Again thank you for your time and assitance.

[selldoor]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

I think it is too long - for me, you would have been better splitting it up
into several questions. I will go through and suggest where I can then others
can comment on that and hopefully fill in the gaps

1 orientation of transistor
I dont think I would want to rely on a one rule fits all though that might be correct, and if datasheet is not available it is more difficult.
I have never even thought about it and always just assumed the diagram
was looking onto the bottom with legs towards me. If testing for shorts only
I dont think it matters
Also it often has the c,e,b marked on the board?

This might help https://www.youtube.com/watch?v=b0jCUsenNsY
fast foward 1min.

2 IC1201 - probably can test for shorts else need power - datasheet
T1201- unlikely to be able to test.


3 Shop Jimmy is very helpful if in doubt ring and ask

4 Q 601 looks bad - test should be valid as it works for the others?
You have them out of the board - yes?

5 Dim Bulb Test
You have probably done it the wrong way round if you remove some components you cannot say those left are ok because the liamp doesnt light- it just means the circuit is incomplete.
The test is that the light does light up then dims as the board powers up
OR glows bright if it doesnt. If it doesnt light at all you have a break in the circuit. You should start with all components in and as there is a short, it should show bright and stay bright - but dont leave it on for long. You then remove and test a component and replace it if bad, then start with the dim bulb test and if it stays bright move on to the next component- remove -test-replace test.
Alternative is just to chance replacing anything you might think has gone
and start with dim bulb test. Its not easy with a complex board like this
as sections are cut off/do not start until conditions are met.

Zener part no at digikey Z4KE200A-E3/54GICT-ND

[Mad Capper]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

selldoor thanks for the info

I tested IC1201 continuity between combinations of pins and only get a beep for pin 7-8. I am not sure if this is how it should be. The only datasheet I could find that is perhaps similar is below and I am not knowledgeable enough to translate it to possible tests one can do with a meter.

The datasheet on this page is for MIP2F30MTSCF not MIP2F30MSSCF which is what the service manual say
http://www.datasheet4u.com/download_new.php?id=813081


Yes, mosfets were out when tested.

Here is the datasheet for the one that is bad



And here is one that is on a 15 LCD monitor that I have laying around that. From my view they are too far out of spec, but what do you all think?

[selldoor]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

Here was budms test from another thread

Check the VCC pin and the Ground pin to see if the MOSFET inside shorted out due to too much B+ feeding the IC with the missing Zener.

I dont think a 600v will do - maybe one of these?
http://www.ebay.co.uk/itm/Silicon-N-...-/190836871503

[Mad Capper]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

I assume for the testing procedure mentioned for IC1201 it has to be soldered in and the check is for continuity between pin 4 Vcc and the board ground as the IC does not have a ground. Needless to say my schematic reading lacks quite a bit.

Ok, so the dim bulb test is for one component out at a time. I was confused because here: https://www.badcaps.net/forum/newrep...reply&p=297745

and the ensuing discussion makes it seem as though you take components out one at a time and then see if the light is light then take another one out, just the opposite of how you described.

[Mad Capper]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

I put everything back in except the D1208 zener and the Q601 mosfet. The light bulb does not flash or glow it stays dark but the relay on the board does click on.

I then put the mosfet back in leaving the zener out and plugged it in again for a split second. The light light bright and I pulled the plug.

Would I be correct to say that the mosfet is the problem and since the light stayed dark without it in that there are no other shorts? Thus would new mosfet and a zener to be safe fix the problem?

I am just trying to get all the problem components sorted out so I don't have to pay for shipping over and over and over, been and done that.

[budm]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

The MOSFET checked as shorted between Source and Drain? if not it may mean that the Gate drive signal is stuck high and cause the MOSFET to be fully on instead of switching on and off at very high frequency. D1208 is not needed for testing purpose.

[Mad Capper]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

The MOSFET checked as shorted between Source and Drain?

I believe the answer is yes.

I tested the mosfets Q601, Q1702, Q1701, Q1602, Q1602 accorinding to the 4 steps here: http://www.sentex.ca/~mec1995/gadgets/mostest.htm

All worked as the test describes except Q601. If I touch the positive lead to the gate then to the drain I get open, if I hold it on the gate for a few seconds then move to the drain it flashes a number then goes open.

I hope I am testing that correct.

Since, as you mention, the zener is not needed for testing then the fact that when the MOSFET is not in the light bulb stays off and when it is in the bulb is bright would mean it is probably the only part that is bad and there are no other shorts, correct?

Thanks

[budm]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

If you do have very low resistance reading between S and D, then yes.

[Mad Capper]

Re: Philips 40PFL3505D/F7 Blows fuse when plugged in

Ok so I will order the parts and put them in and see how things go. Should I still use the light bulb as a fuse?

Out of curiosity what is the difference between using the light bulb as a fuse vs using one like Budm posted in the link below and having a fuse in place on the board then plugging the tv into the outlet on the tester and the tester into the wall?

http://s807.photobucket.com/albums/y...t=DSC01679.jpg