Electronics > Repair
Power supply ripple on UA723 based circuit
RichardM:
I am repairing a spare R&S SMS signal generator and have noticed the ripple on the 5V supply is well above spec. It’s about 60mVrms and should be < 0.4mVrms. I have attached an image of the 5V part of the power supply circuit.
The adjacent +-15v rails have <1mV ripple. There is also a similar small ripple at MP1 on the positive side of C1. The 60mv ripple appears at MP2. I have swapped the UA723 and 741 opamp with new ones but that did not make a difference. Any thoughts on what the most likely culprit is or what to check first is appreciated. Can a noisey T1 or T4 be the reason?
Cheers
Richard
ondraN:
I would suspect C1 in the first place.
RichardM:
Ok, the ripple on C1 at MP1 is 0.2mv and C1 measures above 20,000uf ? Could it still be the problem?
ondraN:
Are some ripple on MP3? It is power suply for 723 and 741 and can cause some problems.
iMo:
Doublecheck the MP1 voltage as well, it could be too small for proper regulation (you want 5.39V out with 8.2V in)..
..and look at the ripple at R12 too..
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