Basic Fuse Question Philips TV

[edy]

I have tested more diodes on the board. Looking at the schematic (see my last photo attached), the MOSFET at Q601 shorted drain to source... and if you follow the source down it grounds through 1ZB36BL Zener diode D608.

Well I happened to find this was the only diode shorted on the board. I completely removed it and I get zero resistance both ways!!!

So I think I need to replace the MOSFET and the Zener and I should be ok? I hope I didn't miss anything.

Now, the MOSFET is 500v 5A but I can get a 500v 4.5v from my local supplier. Is that going to be ok? Or should I go up? And is there any other important number I need to watch out for? And I can't seem to find that Zener diode anywhere on Sayal.com, and not sure the compatible part. So I don't know whether to just buy this stuff from Mouser or Digikey and pay and wait for shopping.

[Vito_R]

Glad you also caught that shorted diode.  If you didn't it would of blown your Mosfet again.  That's why it's so important to double check all components to avoid any surprises.  Also running a quick check of any resistors in that circuit to make sure none have opened up is also a good idea.  I highly recommend you replace the mosfet with an original part and get it from mouser, they seem to have it in stock.  Good luck

[edy]

Thanks, I never thought a simple blown fuse would lead to such an interesting detective game. This was a great exercise for me in learning. I've attached the parts list from page 69 and I can't find that Zener diode anywhere on Mouser or Digikey or Sayal. I want to order that TK5A50D from Mouser but I notice they have 2 options... which do I get? And what equivalent Zener? I can't find 1BZ36BB anywhere.


Looks like this has happened and reported here:

http://www.badcaps.net/forum/showthread.php?t=22454

The more I look the more I find!

[Vito_R]

Thanks, I never thought a simple blown fuse would lead to such an interesting detective game. This was a great exercise for me in learning. I've attached the parts list from page 69 and I can't find that Zener diode anywhere on Mouser or Digikey or Sayal. I want to order that TK5A50D from Mouser but I notice they have 2 options... which do I get? And what equivalent Zener? I can't find 1BZ36BB anywhere.

Thats what troubleshooting is all about, being an electronics detective.

I saw a seller from the UK selling the 1BZ36 on ebay.  Shipping is usually fast from UK to Canada, I recommend that.  See those > ! < marks next to those components means the manufacturer recommends replacement with original components only because they are safety critical.  Try to give the manufacturer a call sometimes you can get lucky and they still have them in stock.  If not you can try to find an equivalent that matches or exceeds the specs of the Zener.  Might want to have a look at this on digikey: http://www.digikey.com/product-detail/en/1N4753A-TAP/1N4753A-TAPCT-ND/3104322 but I still recommend you use the original.

The mosfets both look the same to me.  I would recommend you order at least 2 so you have spares.  Same with the Zener.

I would highly recommend you check R611 that 0.68ohm 2W resistor to see if it's open.  If it is you must replace it or your parts will burn out again.  Desolder one leg and test it.  I would also check R608.  If it would be me I would check all resistors in and around that circuit for any opens.   I also would check the other transistors just to be on the safe side.  At the same time if you have any of those crappy chinese electrolytic capacitors on the board (which you probably do) I would replace them all with Nichicons PW, HE, or HW series after you confirm your board is working again.   Good luck

[edy]

And the plot gets thicker! I read that thread on the previous post from badcaps forum and someone also suggested the transistor Q602 on the gate of the MOSFET may also blow... So I de soldered Q602 and also the same part located at Q656 on the board for comparison.

I used the test for transistor using a multimeter shown here:

http://www.vetco.net/blog/?p=184

The transistor at Q602 showed a voltage drop from emitter to collector in both directions while the good transistor at Q656 showed 0L for both directions (swapping pos/neg leads) as expected for a good NPN. So that is another defective part found....

Note that without unsoldering the good NPN also showed some strange results. The amount of work involved and time is almost economically reaching the limits for this cheap TV. But I don't want it to end up in landfill and I am using this as a learning opportunity.

[Vito_R]

Well that's why I kept saying test all parts connected to that circuit and the remaining transistors.  Better to be safe then sorry and have all those parts burn out again cause we missed a component.  This was definitely a multiple failure and when that happens I just test all semiconductors and resistors for failures just to be sure it doesn't take out my new components if I happen to miss something.  A good electric vacuum pump desoldering tool is our best friend in a situation like this.

[edy]

Hi Vito_r,

Thanks! Yes indeed I took R611 out and it has no continuity... 0L resistance! When will it end! If I have to keep removing components to test this is going to drag on forever... I may as well just find another power supply board and just replace the whole thing. 

[Vito_R]

Hi Vito_r,

Thanks! Yes indeed I took R611 out and it has no continuity... 0L resistance! When will it end! If I have to keep removing components to test this is going to drag on forever... I may as well just find another power supply board and just replace the whole thing. 

You're getting close to the end don't give up.  Just be patient and meticulous and you should be successful with this repair.  Sometimes I find taking a break for a while and coming back to it later is less stressful.  Take the time and do it right so it's not all for nothing.  Keep up the good work.

[Vito_R]

Just want to add that the fellow at the electronics store you went to that sold you the fuse gave you bad advice.  He should never have told you just install the new fuse and see what happens.  This is possibly what caused more failures on your board.  Even the manufacturer mentioned it in the block diagram, make sure you check for all other faulty components before replacing the fuse.  Anyways can't cry over spilled milk.  Just check everything and replace whatever is bad like you're doing.

Update:  I recommend you also check D604 and all surface mount diodes.  Also recommend you re-check the transistors for proper forward voltage and no leakage.  Make sure you don't miss any of them cause there could be more.  IC601 may also be an issue.  Suggest you replace it to be on the safe side while you're ordering parts.  This one is a special situation where you really need to be meticulous and not overlook anything.  If you do that I'm sure you will be successful here.

[Tandy]

The amount of work involved and time is almost economically reaching the limits for this cheap TV. But I don't want it to end up in landfill and I am using this as a learning opportunity.

It is taking a lot of time partly because it is something new to you but if you regularly repair things like this you get a feel for the most common type of fault and it doesn't take so long. Sometimes as components are so cheap I tend to order a handful of components to replace anyway as it takes less time to replace half a dozen components in one go than to remove each one, test it and then order them.

Well done for persevering with it, like you say it is a learning experience and although it is only a chap TV this time what you have learnt troubleshooting the problem may help with more valuable things in the future.

[tom66]

These are crappy FUNAI LCD/LED-LCD TVs. They are not built by Philips, just a re-badge job.

Likely you'll find a shorted diode on the secondary which will take out the badly designed primary side. It is a ringing-choke converter -  a self oscillating flyback (yes in a modern consumer product that's pretty rare.) They are horrible to repair.

[edy]

Yes I saw that.... I keep seeing threads on other boards as well (like badcaps forum) showing various models. In fact, I found an Amazon listing here for a repair kit and I could probably get another power supply board Part# BA21N0F0102... for $20-30 (maybe cheaper on eBay):

http://www.amazon.com/Magnavox-BA21N0F0102-Component-Repair-Kit/dp/B00KTD918K

They are labelled Magnavox, Emerson, Sylvania... all crappy brands. It is unfortunate Philips decided to do this as well and throw their brand name into the crap pile with the rest by doing this.

At this point I am not sure whether it is cheaper just to buy all the parts from Mouser/Digikey and go through the trouble of desoldering and testing, although it is a good exercise if anything in learning how to trouble-shoot and test parts.

I also see on eBay a bunch of "repair kits" which list 7 or 8 items, I presume the most commonly blown parts they have found from experience? That will at least help me track down more faults... Notice none have CAPS.... Only the MOSFET, some associated resistors and diodes and transistors.

[Vito_R]

Going with a repair kit could save you some time in terms of ordering everything individually and possibly from different suppliers.  Just make sure the parts they use are genuine and not some knock off chinese counterfeits you often see on ebay.  That's why whenever possible my personal preference is ordering directly from the big distributors to lessen the chances of any headaches.  Also make sure you check your surface mount components too, diodes or any transistors, D604 could be another potential fault. I would also pay particular attention to R602, R608, Q600, D607, D610, and D640.  Check them for faults and also see if any of those repair kits include those too.  If you really want to keep those crappy electrolytics on the board I would at least at a minimum test all of them with a good esr meter.  After you confirm your board is working again, I don't think it's worth it leaving them there after all the work you've done to repair it.  Why leave crappy caps in there that most likely will eventually fail?  Just my own personal opinion.  Agreed this is well worth the learning opportunity for you and the tough jobs is where you gain the most experience.  Good luck and keep us posted.

[Vito_R]

Just realized this post should really be under the repair category and not under beginners as it has turned into an excellent repair example.  Wonder if it is even possible to move it at this point.  Maybe we can ask Dave ?

[cybertronicify]

Time delay (slow-blow) fuses are used on equipment where there is an inrush current, in other words it needs moor power to start-up. This is typically inductive loads like motors or resistive loads that change rapidly with temperature like light bulbs.

In your TV it is more than likely a standard fast blow fuse.

No! SMPS is the device where very high inrush current is present while primary capacitor is charging. Therefore usually slow blow fuses are used in SMPS. Anyway there is T4A of F4A written on the fuse which will solve the dilemma.

On some SMPS's if the inrush current to the capacitors are too high, they will add a resistor inline so eliminate that. That is why some SMPS's do not spark when plugged in the mains instead that slowly charge the capacitor. Slowly as in a span of 1 second.

[edy]

I thought this was going to be any easy fix too! And I'm a beginner... Little did I know it would be involving so many components. I guess there is a "domino effect" where a component fails and starts taking out more and more parts until finally you have an entire chain or network of components fried.

I'd like to know the time sequence of how things failed until finally the fuse blew. I guess the chain of events can be worked out, looking at "what if". For example, if the MOSFET is first to go... what does it do to the other components around it, and what is the chain reaction until finally the fuse goes? What if that Zener shorted first, or what if the Resistor opened up or transistor shorted... each would have a different effect on the circuit path and voltages and currents as the failed component would effective "change the circuit" and all of the charges flowing through it.

Understanding those can help build a "pattern map" of what parts would typically be involved with each type of failure, depending on which components are affected you can work out what may have failed first and how the entire chain of events occurred.

[Vito_R]

I thought this was going to be any easy fix too! And I'm a beginner... Little did I know it would be involving so many components. I guess there is a "domino effect" where a component fails and starts taking out more and more parts until finally you have an entire chain or network of components fried.

I'd like to know the time sequence of how things failed until finally the fuse blew. I guess the chain of events can be worked out, looking at "what if". For example, if the MOSFET is first to go... what does it do to the other components around it, and what is the chain reaction until finally the fuse goes? What if that Zener shorted first, or what if the Resistor opened up or transistor shorted... each would have a different effect on the circuit path and voltages and currents as the failed component would effective "change the circuit" and all of the charges flowing through it.

Understanding those can help build a "pattern map" of what parts would typically be involved with each type of failure, depending on which components are affected you can work out what may have failed first and how the entire chain of events occurred.

As Tom66 mentioned, this is a crappy power supply with a poor design which was unfortunately used in many different TVs.  However I would highly suspect that replacing the fuse before confirming that there are no faulty components most likely caused the high number of failures to occur.  Those guys working in the electronics stores are not technicians or engineers and usually have little to no background in electronics.  It is hard to say what started it, if I had to guess I would suspect the Zener and/or the source resistor R611 started the problem.

[edy]

I found a bunch of repair power supply component kits. The kits at least point me in the right direction as they list a handful of parts.... So I will check all the parts you mentioned. Hopefully I'm close to discovering them all! Here are some kits or replacements:

http://www.shopjimmy.com/emerson-a2176mpw-001-power-supply-led-board-component-repair-kit.htm

http://www.usefulparts.com/tv-parts/lcd-tv/power-supplies/power-supply-a2176022-from-philips-22pfl4507-f7-a2176ut

I will have to keep hunting for details and then get some help on the Mouser or Digikey order, as I have never dealt with them.

[Vito_R]

Take your time and i'm sure you'll find all of them.  The greatest benefit here is the learning experience you're getting.  Good luck and keep us posted.

[tom66]

They are labelled Magnavox, Emerson, Sylvania... all crappy brands. It is unfortunate Philips decided to do this as well and throw their brand name into the crap pile with the rest by doing this.

Philips got out of the TV business about 2 years ago... along with Toshiba, Sharp, JVC, Hitachi and Sanyo. With the exception of very high-end or large TVs, Toshiba and Sharp are only re-badging crap models now.

[ijchan223]

i wouldn't bother with buying the kit, because you don't learn anything form just swapping components out and you can get the while board on ebay for the same price.

[edy]

I have attached part of the schematic and highlighted in RED the components that are being provided as part of the Repair Kit (which I list below). I have already confirmed that the MOSFET Q501, Resistor R611 and Transistor Q602 are fried on my board. It seems my rectifier diodes D601 through D604 are ok. But I have not checked some of the other components provided in the Kit.... So perhaps the kit will guide me on which parts to check next.

From an electronics failure point of view, it seems these parts are suspect and if something blows it will take most or all of these things out before the voltages and currents settle to a point where they cannot damage the remaining parts. Keep in mind I have no easy way to test the C605 cap with my multimeter and it is best if I just replace it as a matter of fact, and some of the other components.

So do I buy the KIT or the BOARD?

The links below (ShopJimmy) seems to be the most reliable source I found.... If anyone knows another, please let me know. I don't think I will be able to order all those individual parts from Mouser/Digikey and get it under $15 as an individual user. And I have not found the board at less than $40 from any reputable sources on eBay. Also it seems the source below warranties the board for 180 days whereas the kit has no warranty at all (obviously). So I suspect the BOARD will be the best way to go for the replacement.

KIT for $15.57:

http://www.shopjimmy.com/emerson-a2176mpw-001-power-supply-led-board-component-repair-kit.htm

BOARD for $39.43:

http://www.shopjimmy.com/magnavox-a21n0mpw-001-power-supply-led-board.htm#

[Vito_R]

Seems like the repair kit is an affordable option to go with.  Shopjimmy is usually a reliable source for those kits from the feedback I've heard on other forums.  I personally prefer to source my own parts just to be sure of what I'm getting.  But at $15 you can't really go wrong.  You've already learned a lot doing the troubleshooting now it's down to getting those replacements in.  Just a caution reminder, be 100% sure you didn't miss finding any other faulty components on this board because it has a tendency to cascade fail quite easily.  A lot of technicians initially power these boards up after a repair with a variac (variable AC transformer) and slowly bring up the voltage and monitor the board for results.  Another trick techs use is the old light bulb in place of the fuse technique.  This current limits the load so you can initially see if your board is still in a short circuit condition or drawing too much current.  After that you need to remove the bulb and replace the fuse, test, and cross your figures she doesn't blow again.            Good luck 

[edy]

On a bit of a side-track, to test my caps.... since I don't have an ESR meter, I looked at the video posted by w2aew below. I have a function generator that could possibly do about 44kHz max at 1V square and an oscilloscope. Would I be able to get any useful reading doing a test with it? I understand I'm looking for a low resistance in the higher frequencies.

I can test my resistors and diodes with a multimeter, using ohm and diode/continuity settings... even the transistors I can check diode voltage drops and hFE values on my digital multimeter. But the caps I am having trouble with. I am wondering what the easiest way to tell I have a good capacitor.

Here's the video I am referring to and wondering if my 44kHz 1V square would be good enough for any usefulness or if there is some other way I can know my caps are ok:

[Vito_R]

On a bit of a side-track, to test my caps.... since I don't have an ESR meter, I looked at the video posted by w2aew below. I have a function generator that could possibly do about 44kHz max at 1V square and an oscilloscope. Would I be able to get any useful reading doing a test with it? I understand I'm looking for a low resistance in the higher frequencies.

I can test my resistors and diodes with a multimeter, using ohm and diode/continuity settings... even the transistors I can check diode voltage drops and hFE values on my digital multimeter. But the caps I am having trouble with. I am wondering what the easiest way to tell I have a good capacitor.

Here's the video I am referring to and wondering if my 44kHz 1V square would be good enough for any usefulness or if there is some other way I can know my caps are ok:

Using an esr meter is really the most effective way I would recommend.  If you are not sure then just swap them out when you're ordering parts.  The cost is very minimal and you can replace them with some high quality low ESR Japanese caps that are extremely reliable.  Nichicon PW, HE or HW I find are the best but any of the other known brands like Rubycon, United Chemicon, Panasonic, any of their low esr (made for switching power supplies) series are great and extremely reliable.