Busted OScope, I think the transformer is fried!

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Postby Steve Anderson » Tue Feb 09, 2010 6:10 pm

err...so how did you measure the voltage before? You presumably found the 0.02uF cap, one end is ground, the other is terminal 5. To that cap (somehow) the 470 Ohm resistor is connected. In that part of the circuit there are only two 2W resistors, this one and a 27k version. Simply look for a 470 Ohm 2W resistor, confirm visually or with a meter that one end is connected to the cap. Measure its resistance, and at the non-cap end measure the voltage.

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Postby smeezekitty » Wed Feb 10, 2010 9:24 am

Steve Anderson wrote:err...so how did you measure the voltage before? You presumably found the 0.02uF cap, one end is ground, the other is terminal 5. To that cap (somehow) the 470 Ohm resistor is connected. In that part of the circuit there are only two 2W resistors, this one and a 27k version. Simply look for a 470 Ohm 2W resistor, confirm visually or with a meter that one end is connected to the cap. Measure its resistance, and at the non-cap end measure the voltage.

Steve A.

Sorry for asking stupid questions, but is it one of the big fat ones or the little ones?
----edit----
I think i found it.
The color bands say its 680 ohms and it measures at 720 ohms.
It is connected to a 0.02 ceramic capacitor that has one lead connect to ground and another resistor.
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Postby Steve Anderson » Wed Feb 10, 2010 12:26 pm

Modifications were/are done on a product so a change from 470 to 680 Ohms is nothing unusual. 720 Ohms is 6% high...fine...and you have to allow for the accuracy of your meter too, lesser ones are often 5% accurate on resistance, so there's nothing wrong with it. Yes the 2W ones are the largest in that area.

So, checked the raw supply as I requested above?

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Postby smeezekitty » Wed Feb 10, 2010 2:55 pm

Steve Anderson wrote:So, checked the raw supply as I requested above?

397.4v
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Postby Steve Anderson » Wed Feb 10, 2010 3:06 pm

Well I think the next course of action is to replace those two EHT rectifiers. And perhaps the 6CZ5. Sorry, but that's it.

FYI, datasheet for the 5642 attached.

Anyone else following this thread have any other suggestions?

Steve A.
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