DSO138

I bought and mostly assembled one of these DSO138's years ago and use it sparingly off and on kinda like a toy . Recently I had some power supply problems and decided to hang my toy on the DC line of a switching power supply to look for stability issues and loading reactions. I had it on line for a few hours when I started seeing sporadic high speed square waves dancing in and out of frame ,and over the coarse of a couple of days the screen was full of nothing but helter skelter dancing oscillatory square waves -mostly- as if some Dolphin had hacked it! Teh device that was being fed by the supply was stable and problem free so I started trying to read the mind of my little magic white worm box. Board inertial stimulus, moderate temperature cycling and different supply voltage play had little effect .It looked like bad DC instability but the test points read fine to a DVM. I fired up my PACE desolder system and eventually got the entire group of 100uf 16V caps off of the board and after checking my supply of caps for spec with a Sencore Cap/Inductor tester and filtering for both low leakage ,proper cap and less than 6 Ohm ESR ..I replaced the bunch and now all's quiet with the white worm! The old caps tested all over the place with leakage ,value and ESR ranges worthy of predicting Lottery numbers. My advice, IF you buy a DSO138 in kit form ..get fresh 100uf 16V (or 25V if they have the correct lead spacing and aren't too tall) from someplace trustworthy .It's best to do this at the time of intimal building because if you don't have a good desoldering system (Pace,GOOT, or other vacuum assist and precise tip selection available) you can easily wreck the board. My -no probe connected and highest sensitivity setting -background displayed noise is in the sub 20 mv ,and I am going to add a monolithic and Tantalum cap set in parallel with the new 100's to see if that brings it down even further. Even if not further quieted ,it's still a much more useful scope than when "Flipper" was yacking at me!