VESTEL 17IPS61-3 shorted output diodes

[ReeceyBurger123]

Re: Vestel shorted output diodes

Is this stuff suitable for future repairs? http://www.ebay.co.uk/itm/Halnziye-H...-/262588989842


Phew, that's a relief. I was thinking maybe the voltage spike which killed one of the original diodes had also taken out something on the logic board so perhaps the flashing was some kind of error code.



Thanks fam, its great that we have people like you out there uploading this sort of thing for the repair community.

Thats the stuff I use yes its fine, also yeah the flashing Led will stop after it boots up glad to help

[John843883]

Re: Vestel shorted output diodes

Thats the stuff I use yes its fine, also yeah the flashing Led will stop after it boots up glad to help

If I'm ever in Telford again I'll be sure to drop by your shop if I can find it. Last time I was in town I got my head stuck between some railings in wonderland.

[tom66]

Re: Vestel shorted output diodes

where are the spikes originating? is the opto-isolator not reacting fast enough?

Spikes originate from the flyback converter, this is how they all work. When the primary transistor turns off the leakage inductance on the primary causes a voltage spike. This is mostly absorbed by the RCD clamp (resistor+capacitor in parallel with series diode) but only to around 800V or so, usually just a touch below the rating of the primary transistor. This pulse gets multiplied by the ratio of the transformer meaning you can see 100V+ pulses on the secondary. This is also in addition to any secondary-side leakage inductance.

In the Vestel case the secondary transformer is poorly designed and so 300V spikes are seen. The diode ratings are inadequate leading to failure. Most flybacks typically only expose the diodes to 2-3x the nominal output, I suspect these power supplies are designed to operate with a lot of ripple on the primary side (100V+, probably, small caps) and so the transformer is designed like this.

Long and short -> cheap shitty design, easily rectified with a couple pence more, but hey, it's VESTEL. That wouldn't be right!

[ReeceyBurger123]

Re: Vestel shorted output diodes

Awesome however I dont own a shop, Im 17 and work from home atm but glad to help Also lol even I wasn't able to do anything like that at wonderland, town has changed loads since though nothing like it was sadly

[ReeceyBurger123]

Re: Vestel shorted output diodes

Long and short -> cheap shitty design, easily rectified with a couple pence more, but hey, it's VESTEL. That wouldn't be right!

Long time no see Tom, doesnt matter anyway most Tvs nower days fail in under 2 years even if Vestel did correct that theres another issue just around the corner with them.

[stj]

Re: Vestel shorted output diodes

Lol thats probably just melted plastic in that though

nope, same as the tiny tubes - i'v got some here is use on some set-top boxes.

[John843883]

Re: Vestel shorted output diodes

Spikes originate from the flyback converter, this is how they all work. When the primary transistor turns off the leakage inductance on the primary causes a voltage spike. This is mostly absorbed by the RCD clamp (resistor+capacitor in parallel with series diode) but only to around 800V or so, usually just a touch below the rating of the primary transistor. This pulse gets multiplied by the ratio of the transformer meaning you can see 100V+ pulses on the secondary. This is also in addition to any secondary-side leakage inductance.

In the Vestel case the secondary transformer is poorly designed and so 300V spikes are seen. The diode ratings are inadequate leading to failure. Most flybacks typically only expose the diodes to 2-3x the nominal output, I suspect these power supplies are designed to operate with a lot of ripple on the primary side (100V+, probably, small caps) and so the transformer is designed like this.

Long and short -> cheap shitty design, easily rectified with a couple pence more, but hey, it's VESTEL. That wouldn't be right!

This is great information! I wonder why it only happens at startup, maybe the feedback loop is just not stable under certain load conditions. Do the voltage spikes happen every time the TV is powered up from standby or just when its been unplugged from the mains?

Awesome however I dont own a shop, Im 17 and work from home atm but glad to help Also lol even I wasn't able to do anything like that at wonderland, town has changed loads since though nothing like it was sadly

Impressive for such a young age, I think you'll go far.

And yeah most of the larger towns in Shropshire are changing so rapidly, won't be long before they become cities.

[John843883]

Re: Vestel shorted output diodes

it's a very short spike, i wonder if a parallel snubber cap+resistor would squash it?

i have seen that done across schotky rectifiers in lite-on built monitors.

Apologies but I hadn't seen your post until now.

There was already an SMD 1nF + 20 ohm snubber across the diode so theoretically with a bit of tweaking the voltage spike could be reduced to something more sensible, however given the magnitude of the spikes a modified snubber would probably dissipate a decent amount of power under normal operation when the diode see's around 80v.

I suppose a transorb would be ideal in this situation, it could even be mounted in an unpopulated diode placeholder. I've got a few of them in stock and wish I'd tried one now

[ReeceyBurger123]

Re: Vestel shorted output diodes

Cheers also yeah it wont be long before its a city around 20 years or so.

[stj]

Re: Vestel shorted output diodes

the country does not have that long.

[ReeceyBurger123]

Re: Vestel shorted output diodes

Probably not

[John843883]

Re: Vestel shorted output diodes

Just noticed something, is it normal for these sets to emit a low frequency buzz when in use and no video is playing? As I just powered it up now but with no signal being fed to it and the buzzing sounds like its coming from the power supply but could be from the speakers.

[stj]

Re: Vestel shorted output diodes

loose windings on transformers or inductors will do that - if it has a headfone socket you can eliminate the speakers.

[ReeceyBurger123]

Re: Vestel shorted output diodes

Yeah its normaly the little led driver tarfo is the cause normally, use some cable ties to pull the mag back together normally stops it.

[John843883]

Re: Vestel shorted output diodes

loose windings on transformers or inductors will do that - if it has a headfone socket you can eliminate the speakers.

Thanks for the suggestion, I can confirm that the buzzing is still there with headphones connected.

Yeah its normaly the little led driver tarfo is the cause normally, use some cable ties to pull the mag back together normally stops it.

Hi Reece, Is this the inducter that you are referring to inside the red box? Also have you noticed this low frequency buzzing sound too when servicing these vestel boards?

It goes away once the TV is in standby mode.

[ReeceyBurger123]

Re: Vestel shorted output diodes

It could also be the main transformer. Get your ear close and listen to which one is causing it.

[John843883]

Re: Vestel shorted output diodes

It could also be the main transformer. Get your ear close and listen to which one is causing it.

Its difficult to pinpoint, all I'm really concerned about is if it was doing it before I replaced the diodes and if its normal on these models.

Edit: Couple points of interest is the 12v rail is @ 11.3v whilst the 24v is @ 25.2v, I have a scope available but no isolation transformer so probing anything on the primary side is out of bounds.

[stj]

Re: Vestel shorted output diodes

prod them with a bic pen barrel or something,
if you hit the source the sound will change

[John843883]

Re: Vestel shorted output diodes

prod them with a bic pen barrel or something,
if you hit the source the sound will change

I poked all of the inductive components with a plastic card and honestly it sounds like its coming from the speakers but everything is so densely packed together that its hard to tell for sure. I'm very hesitant to disconnect the speakers as there are forum posts about this model popping its audio amp and I can imagine disconnecting them causing unwanted self oscillation.

Should it be safe to scope the speaker terminals for AC hum? As I don't have an isolation transformer and I noticed there is a 4.7 mega ohm resistor connecting LV ground to the HV 0v reference.

Edit: There is most certainly hum coming from the speakers.

[John843883]

Re: Vestel shorted output diodes

I went ahead and scoped the secondary side since I figured some AV equipment out there is earth referenced.

The 24v rail had some mains frequency ripple around 200mV pk-pk whilst the 12v rail was around 100mV, earlier tom66 mentioned that these things might have undersized filter caps on the primary side so maybe this is normal here.

Onto the high frequency component. The 12v rail is pretty bad at around 1v pk-pk even after the LC filter, before the filter its a messy 3-4v of ringing! I compared the junction capacitance of the new diodes to the old ones and it appears the new ones have a much lower junction capacitance so perhaps that's causing higher amplitude peaks if there is less to be charged up and take some of the edge off from the energy stored in the parasitic inductance of the layout.

The 24v rail looked much cleaner with the usual switching induced blip of around 600mV IIRC.

Unfortunately the owner turned up at this point so I had to quickly reassemble the TV. I guess I'll soon find out soon if the buzzing was present prior to the diode incident.