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Random issue with GW Instek GDS-1074B
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MacMan72:
I took the unit apart and cleaned all the button membranes and the contacts on the front panel so we’ll see how that goes. I also checked all the caps on the power supply board with a de-5000. Some of the capacitors were reading double the rated capacitance with the ESR value reading 0.0 (used 120 Hz). Does that mean there are other nearby components that are getting turned on and messing with the reading or that the caps are going bad? Either way, I ordered new low esr Nichicon capacitors and I’m going to recap the whole thing since there are only a few and they are all generic questionable quality caps. Is there any reason not to use low esr caps? I’m a mechanical engineer by trade so I have basic circuit theory knowledge but some of the more advanced concepts I’ve yet to learn.
tautech:

--- Quote from: MacMan72 on July 14, 2023, 11:33:37 am ---I took the unit apart and cleaned all the button membranes and the contacts on the front panel so we’ll see how that goes. I also checked all the caps on the power supply board with a de-5000. Some of the capacitors were reading double the rated capacitance with the ESR value reading 0.0 (used 120 Hz). Does that mean there are other nearby components that are getting turned on and messing with the reading or that the caps are going bad? Either way, I ordered new low esr Nichicon capacitors and I’m going to recap the whole thing since there are only a few and they are all generic questionable quality caps. Is there any reason not to use low esr caps? I’m a mechanical engineer by trade so I have basic circuit theory knowledge but some of the more advanced concepts I’ve yet to learn.

--- End quote ---
SMPS, right ?
Use low ESR caps. Only the HV DC cap sees ~100 Hz while all the others are subjected to 20+ kHz !
MacMan72:
Yeah, pretty sure it’s smps. (I’m an EE noob, be gentle)
So, should I be testing the caps at a higher frequency? I gotta admit, Dave confused me in his video on this concept.
nctnico:

--- Quote from: MacMan72 on July 14, 2023, 11:33:37 am ---I took the unit apart and cleaned all the button membranes and the contacts on the front panel so we’ll see how that goes. I also checked all the caps on the power supply board with a de-5000. Some of the capacitors were reading double the rated capacitance with the ESR value reading 0.0 (used 120 Hz). Does that mean there are other nearby components that are getting turned on and messing with the reading or that the caps are going bad? Either way, I ordered new low esr Nichicon capacitors and I’m going to recap the whole thing since there are only a few and they are all generic questionable quality caps. Is there any reason not to use low esr caps? I’m a mechanical engineer by trade so I have basic circuit theory knowledge but some of the more advanced concepts I’ve yet to learn.

--- End quote ---
If you measured the capacitors in circuit, then you won't get a valid reading. My strong advise is to leave the power supply as it is. You'll likely do more damage than good. IIRC the PSU is a single sided board so it is easy to damage. And you'll want to make sure the board gets soldered properly as to not create a fire hazzard. In your situation, I'd check the solder joints on the mains connector using a magnifier glass and if these are OK, then just close the unit back up. IOW: if it ain't broken, don't ruin it.
MacMan72:
Yeah, that’s good advice, thank you. If the glitch doesn’t happen again, I think I’ll follow that rule. I’ve gotten burned before “fixing” stuff that wasn’t broken.
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