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Old 31st December 2012, 09:53 PM   #61
srinath is offline srinath  United States
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IC451 output to ground - flashes 120 or so and open, like a capacitor would.
After removing fuse f453 from FC454 to ground - open.
T451 pin 2 to ground - open.
Across c462 flashes a resistance and then open. Either side of it to ground, also open.
Removing F453 and across pin 1 and 2 of T451. I read about 3.5 ohm.

My theory - Bad D458. These all seem to check out fine I think.

Or a bad D453. But I cant see that and getting any voltage to pin 2. Maybe It isn't passing proper 1/2 wave rectified ...

OK so my assumption is this - ac @ F454 should get 1/2 wave rectified with D453, R453 cuts it down a bit, then the cap c465 smoothes current, the D458UZ5V1 regulates voltage, and the R454 bleeds a little off it leaving proper smooth and steady 6v @ pin 2. I have 2.82. Since I cant measure ripple or nothing ... I dunno, maybe c465 or r454 bleeding too much.

No clue, I am confused.

Cool.
Srinath.
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Old 31st December 2012, 09:54 PM   #62
srinath is offline srinath  United States
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I could pull D453 from the circuit and power it up and see if I get 6v in pin 4.

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Srinath.
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Old 31st December 2012, 10:33 PM   #63
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Really I am confused. All the resistance checks does not showed a short. Right now the only that can load the voltage is the IC451. Can you check resistance from the input to ground. Also last results can you lift the resistor R455 or it get hot. The reason I do not belief that diode D453 it is causing any problem is that the R453 is 4700 ohms. If you divide the voltage 18 volts /4700 = .003 amps. It will no load the PS.
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Old 31st December 2012, 11:14 PM   #64
srinath is offline srinath  United States
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IC451 input to ground is open.
R455 is just around 14 ohm.

Something is failing when voltage is applied.

I may power it up and try it under power, pulling 1 component out at a time.

Cool.
Srinath.
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Old 31st December 2012, 11:26 PM   #65
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Hi,
What bother me it is that the voltage loaded from 13 volts to almost 2.0 volts and does not blow the fuse and not shorted.
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Old 31st December 2012, 11:45 PM   #66
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Hi,
Just for the heck can you check the voltage at the fuse before the connector and after. I am still think the loaded to the PS should blow the fuse.
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Old 1st January 2013, 04:47 AM   #67
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I suspect u have a dry (cracked) solder problem.
Thoroughly, solder the board first.

Some Qs...

How old is this. Was it kept powered through its life.

Post voltages on the diagram so that it is easy to diagnose.

Gajanan Phadte

Last edited by gmphadte; 1st January 2013 at 04:57 AM. Reason: added content
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Old 1st January 2013, 05:14 AM   #68
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Is R453 good, and also check D458.

Gajanan Phadte
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Old 1st January 2013, 06:02 AM   #69
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Hi,
I double checked the schematic and found that the only thing that can load the voltage low is by the diode D4554, diode D456 or the IC451 short when the voltage it is applied. If one of the 3 shorted will take the voltage low. If you follow the voltage thru the circuit there is nothing else that can loaded the voltage other than the above mention.
The other path it is thru the IC451 and D459 and then the micro loading the voltage. But the voltage at the D459 anode is 2.8 volts and the cathode is at 5.8 volts that will eliminate the micro. The question I have is why the fuse does not blow. The fuse it is 500ma and if you load the voltage from 18 volts to 2 volts it should blow the fuse and the fuse check OKAY. Resistance check does not showed any short. I ran out of suggestion.
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Old 1st January 2013, 03:40 PM   #70
srinath is offline srinath  United States
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The Reciever is about 11 years old, it worked as a 2 channel receiver, not as a surround amp, I found and replaced swollen caps on the dolby board after which it didn't power up. It actually powered up without the dolby board in ... but didn't after replacing the caps. The thing had to have been left idle for a few years before I got it ~2 months ago.

I will test these later today, too much celebratin for 2013, and thanks guys and wish you all a very happy 2013.

I will actually get some ground wire made up, so I can power up the receiver with the board outside, so I have access to testing the board with it powered up.

Is it possible that as the transformer has an internal short when it is warm ? Of course that would soon after fry itself into a goo ...

Cool.
Srinath.
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