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Modern Vestel/Bush DVD

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Jamie
(@jskinner97)
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Well, I say modern. It's nearly 20 years old... Scary or what. Anyway it "features" a Vestel 12PW2600PI-2 PSU.

The DVD player is very "lazy" and most of the time doesn't work, or open the dvd door etc. All the voltages are down to almost half.

You can hear the transformer screaming too. Even with nothing plugged into the PSU board.
I know anything Vestel is plagued with problems, usually the diodes on the primary side, or capacitors on the secondary side but interestingly ALL of these are absolutely fine. None are showing signs of distress, all the caps measure fine, and all the diodes are OK.

As are R40 & R41. So i'm at a bit of a loss with this... Unless the chopper transformer is just dead? 
I've attached the circuit. 

vestel3
vestel2
vestel1
 
Posted : 28/01/2023 5:27 pm
sideband
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How did you test the caps Jamie? Did you do an ESR test or was it just a measurement on a testmeter? Reason I ask is that caps can measure OK on an ordinary testmeter but have woefully poor ESR which would only show up on an ESR meter. Switch mode power supplies need caps with a low ESR to function properly.

 
Posted : 28/01/2023 10:27 pm
Jamie
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@sideband my capacitor meter tests ESR too, only one of the ESRs was high which was replaced. The rest were OK, and capacitance within tolerance. 

Could it be worth replacing all the ones on the secondary and seeing what happens considering there’s only a few?

 
Posted : 29/01/2023 9:06 am
Nuvistor
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The screaming TX and low output may suggest the switching frequency is incorrect. 
It’s too long since  I fixed SMPS to suggest components but what controls the frequency/ mark space ratio of the circuit?

 

Frank

 
Posted : 29/01/2023 9:13 am
crustytv
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Voltages in and out of IC3 and IC2 (optocoupler) would be my point of investigation, referencing the component datasheets. I believe these are key to the switching frequency of the PSU.

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Posted : 29/01/2023 9:36 am
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sideband
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Posted by: @jskinner97

 

Could it be worth replacing all the ones on the secondary and seeing what happens considering there’s only a few?

 

You could do that but make sure you use low ESR caps.....105 degree types. 

 

 
Posted : 29/01/2023 1:46 pm
Jamie
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Posted by: @crustytv

Voltages in and out of IC3 and IC2 (optocoupler) would be my point of investigation, referencing the component datasheets. I believe these are key to the switching frequency of the PSU.


IC3....
Pin 1 0
Pin 2 & 3 Ground
Pin 4 God knows - my meter will not comfortably read AC OR DC and goes nuts.
Pin 5 5.3V
Pin 6 6V
Pin 7 & 8 Ground

Interesting... https://electronics.stackexchange.com/questions/450639/tny264-hisses-when-isnt-load-significantly

image 2023 01 29 182841313
 
Posted : 29/01/2023 6:22 pm
crustytv
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Well, it's time to get the scope out and see what the Tinyswitch-II is actually doing. This document is fantastic, it will help you, it contains a full and detailed description of how it is expected to work. Lots of detail and lots of scope waveforms for you to check for comparison.

https://pdf1.alldatasheet.com/datasheet-pdf/view/34940/POWERINT/TNY267P.html

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Posted : 30/01/2023 9:10 am
Jayceebee
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Pin 5 is only 5.3v, are you sure, I think you may have got pins 4 & 5 reversed possibly? Pin 5 is the connection to the drain of the MOSFET inside the TNY, there should be much more than that but a lot of multimeters will have trouble as there are huge peak voltages here. Be aware that there are two grounds, every thing on the LH side of the chopper TX is with respect to the chassis symbol which is at half mains. Bear this in mind if you do connect a scope, unless you power the DVD via a isolation transformer there could be a big bang if you connect the ground of the scope probe to LHS ground. If you don't have an isolation TX then only make connections to the ground on the RH side of the chopper TX which is connected to the units metal casing. Also with your scope connected to the RH ground you must not make any measurements on the LHS and vice versa.

BTW some of the TNY devices when they only see a small load they can go into something we called Burst Mode where device only works in small bursts, you certainly couldn't hear it normally. A quick look at the link that @crustytv posted doesn't appear to mention it though.

John.

 
Posted : 30/01/2023 3:08 pm
hamid_1
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Personally, before going too deeply into it with an oscilloscope, I would change all the electrolytic capacitors including the mains 400v ones. Bad capacitors often cause switchmode power supplies to make strange noises. Also check the mains bridge rectifier diodes individually - one of them may have gone open-circuit.

I reckon the TNY chip will be OK. They usually fail short-circuit with the top blown off!

 
Posted : 30/01/2023 4:28 pm
Cathovisor
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Posted by: @hamid_1

I reckon the TNY chip will be OK. They usually fail short-circuit with the top blown off!

I've seen that in some professional kit: a seven-legged device (there's a pin missing for creepage) is used in one company's picture monitor to generate a bulk 24V supply that then feeds other devices to generate the rest of the rails. That device too usually lets go with a loud report and a hole in the chip...

 
Posted : 30/01/2023 7:39 pm
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