CRAP VESTEL PSU's--Can we improve them, modify etc?

[Alastair E]

As is well known The PSU's --particularly the 17PW24.xx series are terrible.

Its often found that one of the three strings of diodes in parallel fail short, this can sometimes cause the primary switching MOSFET to short taking with it the controller chip and some resistors too.

Sometimes, just the MOSFET shorts--for no apparent reason.

Tom66 did some excellent work on these horrible boards a while back, and also consulted with a colleague who is a PSU designer--(IF I recall the posting correctly, I apologise in advance if this is wrong).

It appeared the diodes on the output side--all the same type--UF5402, 3A 200V diodes are under-specked.

The PSU Guy deduced/tested the Vestel abortion and found that well over 900V is present at the instant of switch-on and this sometimes causes the 200V rated diodes to short, during that instant that the supply starts up.

As a first stage of mods of these horrors could benefit from would be to change these diodes to something of a higher PIV, a diode--like the 3A 1000V UF5408. This is much the same diode from the same series but with a much higher PIV voltage....
The UF5408 is dirt-cheap, much the same price as the UF5402.....

Ive had Three of these crap supplies with faults this week, Two with shorted diodes, and one blown MOSFET......

Anyone else done much with these things...?

[stj]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

i had one of these, i replaced all the diodes wih UF5408's

UF4007 and UF5408 are 2 things you should keep a small stock of, they can be used in lots of situations.

[Dang]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

I had the same issue with a similar Vestal PSU, all I can really add is Tom66 did say about grouping the diodes very close together and using some epoxy to try and spread the heat between them more evenly, I can't remember exactly why this is so this will need some professional input but it's something to do with the way they draw more current the hotter they get, if one gets notably hotter then the other two it can start drawing most of the current across it leading to it blowing.

My thread: https://www.badcaps.net/forum/showthread.php?t=44404.

[CapLeaker]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

I put higher rated diodes and mosfets. None have come back so far.

[Alastair E]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

Yup--The difference in the heat per diode can cause issues, the hottest hogging the current and getting hotter--But TBH--The diodes dont get all that hot.

Over the years, Ive seen diodes run MUCH hotter--but not fail like these things do

What Ive done in the past, particularly for the top row that seems the most common to fail, is add two more diodes.

--The holes and print are there for them so I just shove 5 new UF5408 in place of the three that were there. I bend them in such a way as they all closely touch side by side too--Maybe that helps, not had a return yet....

The average temp after half-hour is about 60 odd degrees on them. Not excessive....

[Alastair E]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

I put higher rated diodes and mosfets. None have come back so far.

Didnt know they sold VESTEL Rubbish in Canada....??

[CapLeaker]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

Didnt know they sold VESTEL Rubbish in Canada....??

Unfortunately they do.

[tom66]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

Thread in question regarding the design fail: https://www.badcaps.net/forum/showthread.php?t=42137

[Alastair E]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

Ah--Cheers Tom, I did have a quick look for it but couldnt find...

--Seems my memory about the voltages was wrong--but much of what I mentioned still applies...

HER308G you used, Any preference to this diode as opposed to the UF5408...?
They seem to be pretty much matched as far as specs go.....

[ReeceyBurger123]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

They are poor pieces of junk designed to fail, but keeps people like me in business when they fail 1 year later after the customer has brought the set.

[tom66]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

Ah--Cheers Tom, I did have a quick look for it but couldnt find...

--Seems my memory about the voltages was wrong--but much of what I mentioned still applies...

HER308G you used, Any preference to this diode as opposed to the UF5408...?
They seem to be pretty much matched as far as specs go.....

There's no major difference in a power supply like this. I've started using MUR460 myself, being a 4A diode, the 600V rating is sufficient for the abusive Vestel design.

[Alastair E]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

Ah--cool, I wonder if there's any advantage in upping the ratings of the Switcher MOSFETS in these supplies....?

As I recall, The originals are 9A 500V devices, Maybe a 12A 650V device would be better--all things being equal, such as RDS-on and turn-on/off times....

[tom66]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

The 900V rating is important for the snubbers in these PSUs, I wouldn't decrease it. From memory the primary heatsink doesn't run that warm. I don't really think heat is a major factor on any individual device, just the diode inbalance and the peak voltage across the diodes being an issue.

[tom66]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

Part of the problem is also that the FET blows when the diodes short and this causes the associated damage. It wouldn't be half as bad if the power supply went into protection mode with shorted diodes, or at least blew the input fuse.

I suspect the fuse is grossly overrated for the power supply, it is 3.15A time delay. There is no large capacitor (just the little 22uF one) and the PSU has an NTC as well. So, it should be OK with a fuse around 1A range, ultra fast blow. Perhaps it's worth trying one with a fuse like this - it might just blow fast enough to save the FET.

[stj]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

vestel psu's may be crap, but a lot of them have a nice picture - good panels in them.
i have one in front of me - my main workshop tv.
nice optronics panel in it with a bright image and good viewing angle.

[tom66]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

vestel psu's may be crap, but a lot of them have a nice picture - good panels in them.
i have one in front of me - my main workshop tv.
nice optronics panel in it with a bright image and good viewing angle.

Surely you are joking. Almost every Vestel I have seen has a garbage Samsung panel in it. Samsung produce good panels but the panels used in the Vestel TVs are just terrible. Black level, motion response, colour saturation/accuracy and viewing angle are all very poor. About the only two Vestels I have had with decent picture are a Toshiba Vestel with an LG FHD 1080p panel, and an old Goodmans one with an AU Optronics panel. But their modern ones using made in Turkey Samsung panels are dreadful.

[Alastair E]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

Yup--Ive a Toshiba Vestel here at the mo....

Think its an AUO panel--720p, Not a bad picture,--nothing to write home about--But most of them are pretty horrible, The Samsung panels as Tom says--Awful--Hardly worth fixing!

[stj]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

if it had a samsung or sharp panel i would have scrapped it!

it was scrap from a customer - water damaged tuner.
i just ripped the rust-box tuner out and use the scart input.

[tom66]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

I haven't ever seen a Vestel with a Sharp panel. Generally Sharp panels are excellent for reliability and PQ, but they have an awful pentile style layout which makes them bad for computer monitors.

[stj]

Re: CRAP VESTEL PSU's--Can we improve them, modify etc?

sharp are o.k. if your infront of them, but the viewing angle is absolute crap compared to an AUO.
so o.k. for a monitor i suppose, but not good for a tv.