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Old 10th Dec 2006, 10:58 am   #1
cornboats
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Default Philips k35 - Dead on start-up

Having resolved bright blue picture, I started to take scope results from test points.

I started with test point 13 -supply board and got a good likeness. Couldn't get a result from test point 10 -terminal 14 - so moved the probe hook on the terminal I'd soldered on to aid testing. The set was heard to power off then on again as I moved the hook, then the set went off completely.

I checked on-board fuses and found rectification board -U2, 2 amp blown. Changed, but set will not power up. Red light comes on when mains is switched on but when channel is selected, light goes off.

Some voltages are present on rectification board.

12v to supply board U11 (this included overprotection circuit)
There are 2 x 3.5K resistors in series before this output that are getting really hot, though.
300v is present which goes to chopper.
There should be a 40v coming in from LOPT, but as this is driven from supply board I thiought this could be why it's only 26v.

Any ideas would be gratefully seized upon.
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Old 11th Dec 2006, 2:25 pm   #2
flyingtech55
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Default Re: Phillips k35-Dead on start up

Hi Cornboats

I think (note think, my forgettery becomes more and more capacious daily) the two resistors are only used to start the set up. When the line stage starts up, it takes over and supplies the running supply. However as the line stage isn't running now the start supply is sweating a bit.

I am however happy to stand corrected if I am getting confused (again).

TimR
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Old 11th Dec 2006, 5:32 pm   #3
Welsh Anorak
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Default Re: Phillips k35-Dead on start up

Hi
Check the chopper transistor isn't short - it doesn't blow the fuse if it is, unusually. Then suspect the TDA chopper control IC on the power board (second one in). As the set isn't tripping, I'd expect the fault to be very near to that IC.
Good luck!
Glyn
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Old 11th Dec 2006, 6:26 pm   #4
cornboats
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Default Re: Phillips k35-Dead on start up

Glyn and Tim R

Many thanks for your comments I'll check out and advise via forum.
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Old 12th Dec 2006, 10:37 am   #5
cornboats
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Default Re: Phillips k35-Dead on start up

Glyn. Checked chopper out. It was shorting on all three pins. The fuse did blow but only the once. I only hope it didn't take the IC out with it, but I am not going to know until I find a replacement transistor.
"BU426V" .

Dave
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Old 12th Dec 2006, 6:48 pm   #6
Welsh Anorak
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Default Re: Phillips k35-Dead on start up

Hi
You may find a BU426V a bit hard to find - a BU508A will work fine in that position if you've one to hand.
Hopefully the IC will be fine.
Glyn
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