Author Topic: DVD player "Tevion DVD 8000", resistor on power board charred beyond recognition  (Read 200 times)

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Offline Naluto

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  • Posts: 3
  • Country: de
Hello,
I have an old DVD player, "Tevion DVD 8000", that stopped powering on some time ago.

There are pictures of the PCB and a rudimentary schematic of the primary side in the attachments.

I already opened it up once a few months ago and found:
A cap (C15) on the secondary side slightly bulged and a small brown spot can be seen. There is also some brown gunk at one spot on the PCB where C15 used to be. (And at the bottom of the capacitor itself.)
The plasticcover of C9 is torn, but it looks fine beside that.
C4 also has similar gunk on it, but it almost looks like this was applied intentionally.

The resistor R5 was charred so much that I couldn't read the colourcode anymore. The PCB is also charred at the spot where R5 used to be.

When opened the DVD player that time, I desoldered the capacitors C4, C9 and C15 and the resistors R2, R3 and R5.
I also made pictures of the components back then, but I can't find them anymore.   :-\
The caps are still here, but the resistors are gone. Guess I put them somewhere and forgotten they were.
But I don't have the tools to measure if the caps are still okay.

What I wrote down:
R2 measured: 10 Ohm, colourcode 10 Ohm
R3 measured: 9 kOhm, colourcode 9.1 kOhm
R5 measured: 140 Ohm, colourcode N/A

C4: 400V 22uF
C9: 100V 1uF
C15: 10V 2200uF



Main components on the primary side of the power board:

ST VIPer22A SMPS (Link to datasheet)
EL817B photocoupler (Link to datasheet)
2N5551 Transistor (Link to datasheet)
Transformer BCK-28-0480


The resistor that burned out is R5 which is the base resistor for the transistor Q2.
The question is, how do I figure out what value R5 is supposed to be and why it was destroyed?

The VIPer chip seems fine from a visual inspection, the drain source junction isn't shorted out.
In the datasheet I read that:
I_FB,max = 3mA
U_FB "useful range" 0...1V
I_FB,shutdown = 0,9mA

U_DD,max = 38...46V
U_DD,off = 7...9V
U_DD,on = 13...16V

But I don't know what voltage is present at pins P2 and P3 of the transformer. And what current is suposed to go into the FB pin in normal operation..

Any suggestions on how I can troubleshoot and fix this?
 

Offline fzabkar

  • Frequent Contributor
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  • Posts: 525
  • Country: au
Q2 and ZD1 constitute a simple linear regulator. The Vdd pin of the Viper IC probably sits at 18V during normal operation (according to the datasheet). Of course that can vary, depending on the design. I suspect that ZD1 is probably shorted, in which case that would explain why R5 burned up.

I suspect that ZD1 may be an 18V, 400mW Zener.

R5 would be calculated by measuring the voltage drop across it at a particular Zener current.

I would replace both C6 and C9. These are the capacitors that commonly give rise to startup faults.

« Last Edit: December 19, 2019, 03:13:57 am by fzabkar »
 


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