Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Looking at the position of the holes both diodes in that package are required to be working. I've tried to draw it on your photo. It need to be replaced.

Ok, today I will try to buy another Shottky with minimum 2x5A/60V. Seriously, this vestel bastards are absolute idiots. Using doble shottky without balancing means that the load on the one of the skottky will be higher than on the other. This is design, prone to faults.

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

OK, I bought MBR20100CT, so practically I doubled the rating of the previous Shottky. MBR20100CT is 20A(10A per leg), when the original Shottky is rated 10A(5A per leg). When the volgate of the original shottky is 60V, I am planning to replace it with shottky with 100V rating.
Is this good enough?

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

If it's higher rated then that should be fine but make sure the pin out is the same as in post #32

Looking at the specifications for the MBR20100CT you need an insulation mounting kit and some silicone grease or equivalent to mount it without it shorting to the heatsink.

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Looking at the specifications for the MBR20100CT you need an insulation mounting kit and some silicone grease or equivalent to mount it without it shorting to the heatsink.

Yes, I bought insulation mounting kits. Two kinds of em. One of the pads is silicone rubber, the other is mica. Which is better?

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Yes, I bought insulation mounting kits. Two kinds of em. One of the pads is silicone rubber, the other is mica. Which is better?

I've used both types. What is important is that after you mount the diode you check with your ohm meter that there is no connection between the middle leg to the heatsink.

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Maybe I found out the reason for the short circuit in the shottky. The thermal grease between the radiator and the shottky, and the transistors and the radiator has dried up. The only thing left is a white residue, which looks like a dust.

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

So, the TV is now in working condition. The problem was indeed the shottky diode.
Before registering here, I googled all the problems with this power supplies and none of the results mentioned anything about the problem with the Shottky diode on the secondary of the main transformer.
You have a BIG thank you! from me. Indeed, you helped me so much in the resolving of this issue.

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Glad to see you have it working again.

[ReeceyBurger123]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Good work both you.

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

I'm requesting an action from a moderator. Please, change the title of the topic - add the following text "Solved - Q829"
Unfortunately, I can't do it myself, because I cannot edit the first(mine) post in the topic.

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Anyone reading through this thread will see your answer to the repair so you don't need to alter the title.

[ReeceyBurger123]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

Message Topcat hes on spot and will sort it.

[momaka]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

So, the TV is now in working condition. The problem was indeed the shottky diode.

Nice, great to hear you got the TV working again.

Before registering here, I googled all the problems with this power supplies and none of the results mentioned anything about the problem with the Shottky diode on the secondary of the main transformer.

Vestel TV sets are know around here (on BCN) for blown/burned/shorted output rectifiers (sometimes not even schottkys but regular fast-recovery diodes!).

The one mistake they most often do is install regular diodes in parallel, expecting the current handling capability to increase. But without any thermal coupling, one of the diodes will always run hotter than the other, causing a runaway, and eventually burning out.

So yeah, if you see a Vestel set with no power, maybe you can score yourself another TV for cheap and fix it.

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

The one mistake they most often do is install regular diodes in parallel, expecting the current handling capability to increase. But without any thermal coupling, one of the diodes will always run hotter than the other, causing a runaway, and eventually burning out.)

I really don't understand why the hell they would install 2 regular diodes in parallel, instead of one with double current capacity.
The PSU I have yesterday repaired also has 2 diodes in parallel
Perhaps the make their TV's only to survive the warranty period. This is why they make such a stupid(and maybe deliberate) mistakes.
--------
The usual practice for me is to replace faulty components with a components with higher ratings - current&voltage, but not capacitance, because this may lead to unexpected consequences, because the design of some signal circuits may count on certain capacitance and ESR to function properly.
---
p.s I really hope that my english is not so terrific and is understandable

[dick_barton]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

If they use two individual diodes then do what ReeceyBurger123 says and thermally glue them together so they run at the same temperature.

[televizora]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

If they use two individual diodes then do what ReeceyBurger123 says and thermally glue them together so they run at the same temperature.

If something happens, I will replace both diodes with one double Shottky on heatsink.

[momaka]

Re: Crown CCT3207W(Vestel 17MB08P-5 chasis) stuck in standby

I really don't understand why the hell they would install 2 regular diodes in parallel, instead of one with double current capacity.

Because... this is Vestel.

Perhaps the make their TV's only to survive the warranty period. This is why they make such a stupid(and maybe deliberate) mistakes.

The world economy has to keep going.
How else would we have constant economic growth?

The usual practice for me is to replace faulty components with a components with higher ratings - current&voltage, but not capacitance, because this may lead to unexpected consequences, because the design of some signal circuits may count on certain capacitance and ESR to function properly.

Actually, increasing the capacitance on the output of a power supplies is usually okay in most cases. I've done it many times. Only one particular brand of computer power supply become unstable. Just don't change the value of small caps near chips, as those could be used for timing or certain filtering - those are the only caps I don't experiment with new values.

p.s I really hope that my english is not so terrific and is understandable

It is fine. I had no problems understanding you at all.

If they use two individual diodes then do what ReeceyBurger123 says and thermally glue them together so they run at the same temperature.

That won't help much. The epoxy cases of diodes are not very good thermal conductors. You are better off soldering their leads very close together with thick copper wire.

But even that still won't be the same as having two diodes manufactured on the same die together. That's why in PC power supplies, for example, even if there are two rectifiers in parallel and attached to the same heatsink (back to back), you still won't get twice the current rating. Typically 1.5 times the individual current rating is about as good as it gets.

If something happens, I will replace both diodes with one double Shottky on heatsink.

Exactly!
That will be so much better. And you will get improved efficiency, so that means less heat inside the TV, and you capacitors will live longer.