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KV25F2U standby light flashes twice - help
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PostPosted: Sun Dec 10, 2006 11:44 am    Post subject: KV25F2U standby light flashes twice - help Reply with quote

Hi,

I have a Sony KV25F2U, it gave up few days ago. Displays picture/sound for 2-3 seconds then turns off. Then the standby light flashes twice with a pause in bwtween.

When I removed the cover, I noticed a lot of white 'snow' like dust, so hoovered it out as much as I could as I didnt want to damage any componebts.

I have seen same issues on this board but for different models, I think it was kv28f3u?, but not sure if it will apply to my model.

So any help will be much appreciated.

Thanks.
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Frank
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PostPosted: Mon Dec 11, 2006 12:11 am    Post subject: Reply with quote

Two blinks - B+ over current protection (OCP), unit goes to the standby mode then displays the 2 blink fault. Could be a short in the power supply of any of the circuits
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PostPosted: Mon Dec 11, 2006 5:35 pm    Post subject: Reply with quote

Frank wrote:
Could be a short in the power supply of any of the circuits


Thanks for your reply Frank, any ideas how I cab narrow down the root cause?

Where should I start looking fir this s/c?
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Guest






PostPosted: Tue Dec 12, 2006 1:31 am    Post subject: Reply with quote

H.OUT (Q5030) is shorted. (D board)
• +B PWM (Q5003) is shorted. (D board)
• IC9001,9002, 9003 is shorted.(C board)
check these out.
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gary



Joined: 05 Apr 2005
Posts: 584
Location: MANCHESTER, uk

PostPosted: Tue Dec 12, 2006 9:30 am    Post subject: Reply with quote

if the picture appears briefly after start up the line output transistor must be ok, i have had a couple of these sets wwhich were doing a similar thing, the cause was the low value current monitoring resistor R608 on the ht rail, it had risen very slightly in value from .47 ohms to approx .7 ohm, the give away was if the crt base was removed from the tube the set would run all day the slight increase in current when crt was producing a picture was enough to trigger the the over current protection circuit.
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PostPosted: Tue Dec 12, 2006 7:52 pm    Post subject: Reply with quote

Thanks for replying.
gary wrote:
low value current monitoring resistor R608 on the ht rail, it had risen very slightly in value from .47 ohms to approx .7 ohm

I measured it, my meter showed 1ohm so I went and bought one. But before soldering the new, I thought I'd measure it. My meter also showed a reading of 1ohm again.

Does that mean the original is OK? and my meter is not read less than 1ohm?

Is this a 'fusing' resistor?

Quote:

H.OUT (Q5030) is shorted. (D board)
• +B PWM (Q5003) is shorted. (D board)
• IC9001,9002, 9003 is shorted.(C board)
check these out.

Are they all faulty? How would I go on about checking these out?
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Frank
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PostPosted: Wed Dec 13, 2006 12:47 am    Post subject: Reply with quote

if you say r608 gets 1.00 ohms do what gary sais get a resistor with .65ohms.
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gary



Joined: 05 Apr 2005
Posts: 584
Location: MANCHESTER, uk

PostPosted: Wed Dec 13, 2006 9:49 am    Post subject: Reply with quote

RESISTOR MUST BE .47R IT IS A SAFETY CRITICAL ITEM, YOUR METER WILL BE MEASURING THE RESISTANCE OF YOUR LEADS AS WELL, SHORT THE LEADS TOGETHER THEN SUBTRACT THAT VALUE FROM THE READING ACROSS THE RESISTOR, THIS IS A COMMON PROBLEM WHEN MEASURING LOW VALUE RESISTORS.
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PostPosted: Wed Dec 13, 2006 4:37 pm    Post subject: Reply with quote

Frank wrote:
if you say r608 gets 1.00 ohms do what gary sais get a resistor with .65ohms.


R608 and the new one I bought, they both read 1.00 ohm, so I assumed R608 is OK as it was same value reading as the new one.....

But I'll substract the lead reading, and see what I get.

thanks.
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Guest






PostPosted: Thu Dec 14, 2006 8:40 am    Post subject: Reply with quote

gary wrote:
SHORT THE LEADS TOGETHER THEN SUBTRACT THAT VALUE FROM THE READING ACROSS THE RESISTOR.


When I short the leads, the values jump all over the place, ranging from 1-3.5.
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