Trying to fix broken PSU in a Philips 46PFL8008S/12 TV

[dogbert17]

Hi,

this is my first message ever on the eevblog forum so apologies in advance if I make any stupid mistakes.

My sisters TV failed a couple of weeks ago, it just went dead, no picture no standby light, no nothing. The TV being five years old was promptly replaced with a new set, a Sony this time. Anyways my sister gave the TV to me in the hope that I would be able to repair it. I'm quite the noob when it comes to stuff like this. Previously I've replaced broken caps in sundry equipment but this time it doesn't seem to be the caps.

I opened the TV and checked the PSU, which has the designation FSP163-4FS02. It didn't take me long to figure out that the fuse was blown, so I quickly got hold of the appropriate replacement (several just in case). I replaced the fuse, put the TV back together and connected the mains lead ...

baaam

well from within the TV a crack could be heard and then nothing 

I have now opened the TV again and, surprise, the fuse had blown. Now to be fair, just replacing the fuse was probably not going to fix anything, there's usually a reason for a fuse to go bad. So, after having made sure that the caps were discharged I started to check components hoping to find something faulty.

I have found three broken components so far, one shorted diode (see below) and two failed mosfets (FDPF 9N50NZ), perhaps that's enough to cause the fuse to pop. Since there might be more failed components in the PSU I will have to continue my search tomorrow. In the meantime I have two questions:

1. I'm unable to identify the shorted diode which makes it difficult to order a replacement. The cathode band is red, or possibly brown, and the only text on the diode is T2D 20, the last digit is underlined. The diode is next to an IC marked BD5AQ B117H NYA. Does anyone know what kind of diode this is and what a suitable replacement might be?

2. There are some resistors on the board with 'strange' markings and very low or no resistance. One of them has, unless my eyes are deceiving me, the following color codes: Brown - Green - Silver - Gold - Green. I haven't seen such markings before, what do they mean?

Best regards,

Jan-Olof

[orbanp]

Hi Jan-Olof,

Chances are that the IC is a B117H, here is the datasheet on it:
https://pdf1.alldatasheet.com/datasheet-pdf/view/585134/FAIRCHILD/FSB117HNY.html

See if the circuit around that IC matches the application example in the datasheet (Fig. 29, Pg. 15).
The circuit on the primary side of the transformer would probably be the same, while the secondary might differ based on the supply voltages required in that TV.
The feedback control with the opto and stabilizer IC (TL431 or equivalent) would be there.
Based on that, and reading through the datasheet, you can check out the components.
The IC, with the FET in it, could also be suspect.
You can also pick equivalent diodes, resistors easily, based on the info in the datasheet.

EDIT:
You can also "upgrade" the controller chip, if that is the one used, looks like the chips (117 - 127 - 147) differ from each other only in the max current rating.

EDIT2:
Having looked at the picture you enclosed, the PS looks a bit more complex than the application circuit for that IC.
I did find a service manual for the Philips 8008 series TVs:
http://tel-spb.ru/files/philips_chassis_qfu1-2e_la.rar
They claim the PS board is a "black box", no service info on it, just a block diagram (Pg. 46).
I guess you need to trace out the schematics for the individual PSs.

The diode next to the FSB117 IC is probably "Ddd" in the app circuit, an 1N4935, a fast switching diode.
The resistor could be 0.15 Ohm, 5%, except for that last green band?

I still believe the board is repairable, by piecing together all the information.

Good luck, Peter

[dogbert17]

Hello, Peter,

many thanks for your reply. I have tried to continue researching the the 'mysterious diode' and I'm starting to believe that an equivalent (same ?) diode might be ST02D-170 from Shindengen. Do you think that diode could be a suitable replacement?

>The IC, with the FET in it, could also be suspect.

Interesting, do you know if there's a way to test the IC with a DMM or should I simply replace it as a matter of course?

Again, thanks for your reply.

Best regards,

Jan-Olof

[orbanp]

Hi Jan-Olof,

That ST02D-170 diode is a ZTVS diode, a transient voltage suppressor diode, for nominal 170V.
A ZTVS diode is an over voltage protection diode, similar to a 170V Zener diode.
You need to trace out where that mystery diode is connected, if it is indeed for some overvoltage protection, or if it is that diode supplying the IC with power, as shown in the datasheet.
Replace accordingly.
A ZTVS diode only "works" if there is a surge, or overvoltage, it is protecting other, more expensive components.
In normal operation, when there is no overvoltage, the diode is not "on", it can be left out temporarily.

From the datasheet of the FSB117H it looks that the internal FET can not be tested simply just by some external DMM measurement.
It is lot easier just to replace it, it should not be that expensive, eBay is a possible source.

Regards, Peter

[dogbert17]

Hello again Peter,

Looking at the back of the PSU board it seems as if one end of the diode is connected to pins 6,7 and 8 of the B117H while the other end winds itself to the large (filter ?) caps on the other side. Since I'm more or less a noob at reading circuits I have included a picture as well. Pins 6-8 on the B117H are marked drain.

Best regards,

Jan-Olof

[orbanp]

Hi Jan-Olof,

It is hard to trace the schematics just from two pictures!
But at least the resolution is good enough!

D501 is parallel with the primary of the transformer. (Open the FSB117 datasheet on Pg. 15)
The top end of that transformer is getting the rectified (+) mains voltage, if I see it correctly from the PCB.
BD101 bridge rectifier get the mains. The rectified (+) and (-) goes through L603. The (-) is the ground on the live side, depicted with that triangular horizontal bars in the datasheet.
The (+) goes through L601, D602, FB601, J102. That point is marked by a (+) on the back side of the PCB.
From then on it goes through FB501, R505 (red red silver, 0.22 Ohm) to the top end of the transformer.
Jx are jumper wires, FBx are ferrite beads on pieces of wire, D602 is in the forward direction, meaning the transformer gets the "whole" rectified mains voltage.
If I am correct, you guys have 220V mains over there, so the rectified mains (peak voltage) would be close to 310VDC. So a 170V Zener, a ST02D-170 diode could not be used there as D501!
I would rather go with a "regular" 1N4007, as shown in the datasheet.
That diode clamps the reverse voltage induced in the transformer when the FET is turned off.
Interestingly they do not have a resistor and a cap in series with the diode, like Rsn1, Csn1 in the datasheet.

On second thought, you could check if the FET in IC501, the FSB117, is shorted out with a DMM.
See if the drain (pins 6, 7, 8 ) is shorted to the ground (pin 1). Though there is an internal current sense resistor in the IC, from the source of the FET to the ground. See the internal block diagram of the IC on Pg. 3. That resistor should not be too high.
That short would probably blow the fuse.

Regards, Peter

[grant1842]

If that fuse went open again then there is  a shorted component most likely .
I see Bridge Rectifiers go short alot and diodes, and the Chopping Fets.
I would put your DMM probes across those components and I bet you find one shorted Hope that helps

P.S Safety first ....... Be careful of Hot side of a switching power supply

[dogbert17]

Hi Peter and grant1842,

>See if the drain (pins 6, 7, 8 ) is shorted to the ground (pin 1).

It doesn't seem to be shorted (according to my DMM) but I guess I'll exchange it anyways. I'll also go for a 1N4007 unless you have another suggestion.

I find it a bit odd that google can't uncover anything useful about the diode marked T2D 20. There are lots of threads on badcaps about similar diode markings, e.g. T2D 80, T2D 93 etc but no one seems to be able to positively identify them.

I'll continue to check for other broken components before placing an order for new ones.

Best regards,

Jan-Olof

[orbanp]

Hi Jan-Olof,

I did find a ST02D-200 diode too, a ZTVS diode with the highest voltage rating (200V), but that would be still too low.
If you go with the 1N4007 diode, do use the cap and resistor (R_SN1, C_SN1) in series with it as well, as shown on Pg. 15, the application example in the datasheet.
I am sure the manufacturers tested that circuit well.

Regards, Peter

[dogbert17]

Hi again,

I haven't had much time to work on the TV the last few weeks, but I have now made some progress. So here's what has happened since:

I have replaced two obviously broken mosfet's, they were marked FDPF 9N50NZ. I was unable to find this component in stock at the large distributors, i.e. Mouser and Digikey, nor was I able to find a proper datasheet for it. Well, I found links to what was supposedly the datasheet but all that came up was a document stating that a load of different components were to be changed in some manner, no data about the component. Quite strange actually, perhaps it's discontinued.

Anyway, taking a risk I ordered two FDPF 8N50NZ and installed them, plus a new fuse of course 

After having put everything together again I connected the TV to the mains and ... no load bang this time but alas nor did I get any picture. All I have is the standby light, better than nothing I guess. The light blinks three times and after a couple of seconds it blinks three times again and after yet another few seconds another three blinks, you get the idea.

So my question now is, does anyone know what the three blinks might signify and what should I do next?

Also, in one of my previous messages I mentioned a shorted diode (D 501 on the picture). It turned out, when testing it out of circuit, that it wasn't shorted at all but it definitely seems shorted when in circuit. Is that the way it's supposed to be?

Thanks for you patience.

Best regards,

Jan-Olof

[station240]

According to the service manual linked earlier, and it's slightly confusing description of the error codes.
3 blinks means 12V problem.

Use the diagram on page 58 of the manual to check all the 12V rails are present. Notice how one 12V powers half the set, it's probably that one.

[maki]

Hello Jan-Olof
did you fixed your TV?
If so, can you share your findings?