Electronics > Beginners

Why 2 transformers? (pic)

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wraper:
C16 film cap sometimes goes bad too.

billbyrd1945:
Sorry. I thought I stated earlier that most everything that I could find a part number for was replaced even when my primitive testing showed them to be good. Replaced every cap even though none of them APPEARED to be bad. I still don't know how you know IC1 is a TL494. But you're right. It is.

Shock:

--- Quote from: billbyrd1945 on January 14, 2019, 02:25:36 am ---Is there a more sophisticated way to determine whether one or both of them is bad?

--- End quote ---

Unlikely to be them so I wouldn't go deeper than a resistance check. Normally you would use the  divide and conquer (aka half splitting or 50/50) technique by checking the output, feedback and switching.

If you suspect the transformer there are a few ways to check transformers aside from swapping out or putting the faulty into a known good board. Signal generator and oscilloscope, measuring live with oscilloscope with high voltage active differential probe, using ring tester and also few home brew inductive methods.

Shock:
Seen this video at all? Always pays to dive into google and lookup on the model and board part numbers. Especially consumer gear it's probably been fixed a hundred times already.

soldar:

--- Quote from: billbyrd1945 on January 14, 2019, 12:42:13 am --- What I don't understand is why I would need two transformers on one power supply.
--- End quote ---
You have one transformer to isolate galvanicaly the output from the (mains) input. Then you need to have a loop back from the output to the input for the control. Most PSU's have the control circuitry on the mains side and use an optoisolator for the feedback loop. This one, instead, has the control part on the output side and the second transformer drives the switches while providing the necessary isolation.

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