Testing rectifier diode.

Thread Starter

Pabas

Joined Dec 24, 2020
27
Hi there. Frost of all I'm a noob when it comes to electronic repairs. My knowledge is very limited. I have TV power supply. Which is not outputting any voltage to main board. But that's not a point I have rectifier diode N4007 and on start it has 236V AC and on the other side just 4V DC, so rest of main caps has just 4V, is it faulty? I test it and it seems to be ok one side is closed other has 0.56v. As I said I don't really know how them things work like. What I read this diode converting AC to DC. But is it fine when 236 DC going to 4v DC?
 

dendad

Joined Feb 20, 2016
3,781
I think you need to post a circuit.
But, to have 236VAC on one side and 4VDC on the other, sounds like an open diode to me.
With the power removed, measure for any voltage remaining, and when it is zero, use your multi meter on the diode test, often a sub menu of the OHMS range, and you should have a reading of open one way across the diode, and around 0.7V the other way.
But you may have done that if the 0.56V is what you mean.
Can you post a picture or more info?
 

dendad

Joined Feb 20, 2016
3,781
I just had a thought. If this is in the switch mode supply, the measured 235VAC may be noise disturbing your meter, but a 1N4007, if it is a "1"N4007, should not be used at high frequencies.
But, if this is the mains 235VAC, PLEASE get someone who knows what they are doing to fix it as these devices can be very deadly.

That said, most often, the fault is the electrolytic caps in the power supply drying out, so remove and measure them.
 

Thread Starter

Pabas

Joined Dec 24, 2020
27
Sure I' ll post picture and test this diode once more as soon as I finish work. About caps, all been desoldered and checked with esr meter. All except one that I replaced measures fine. But board is still dead.
P.s sorry for my poor English.
 

Thread Starter

Pabas

Joined Dec 24, 2020
27
Ok Im home that's photos of board not sure which areas you' re lookin for. If you need any more just let me know.
1617144908528126795962790660879.jpg
16171450197264295356109797815791.jpg16171450536127702374111383734046.jpgSuspected diode is marked as DB809 Attaching schematics as well. Thanks in advance!
 

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