When ahead and check PSU and replaced a few out of specs components and check rails, thankfully I do as found a few out of tolerance components that would have shorted and taken out rail.
I did the same thing on my 2235A, replaced the Rifas and the Schaffner line filter. The caps all seemed good. Runs like a charm but good thing I replaced the rifas because they already had hairline cracks.
Yeah, the reason capacitors measure "higher" in capacitance is because they leak DC as they begin to develop a short. Leaking DC causes the tester to record a longer time for them to charge, fooling the tester into thinking they have higher capacitance. An LCR meter which measures the phase shift of a known frequency AC signal (often 100 kHz, but many are configurable) will not be fooled by the DC leakage current
Yep exactly. A LCR meter definitely way more accurate, most ESR meters are not that great, plus the fact they only measure ESR and not other parameters like a LCR meter would, the Peak ESR meter is handy at times as small and better then most as test at 50 to 100 KHZ but usually just use my DER-5000 LCR meter to test when sorting components and need accurate. Oscilloscope another good way to test capacitors. Yep those 3 capacitors that measure high were definitely going to short when they leak they needed to go. Kind of glad tested them as originally just was going to replace the infamous Rifa X/Y class capacitors that love to short as casing cracks and absorbs moisture in paper over the years. Usually don’t replace components until they go bad but in this case glad I caught it otherwise they would have shorted and took that rail out.
I have a 2235A that won't start up after I replaced the SCR in the crowbar circuit. When I got the scope it did start up and showed a trace but the amplification was all wrong and the power rails were way off. The SCR itself was actually missing (I think a previous owner had desoldered it because it was tripping). Have you ever debugged that? I'm not sure if the SCR is too sensitive (maybe the Zener for it is bad) or if something else is bad and the crowbar is doing its job correctly
I had one that did that and had to replace the controller, drive circuit on that supply and resolve the issues and voltage rails when back to normal and crowbar circuit wasn’t shutting down power supply as it designed to do, yes has people remove as well. I gave that scope to a friend that also works in reel to reel decks as he needed one, which he uses to this day. Definitely a great scope worth getting going, once you work out the issues as has dual time bases and you can zoom in using B time base and setting B delay. There definitely something wrong with that supply and reason person removed the SCR thyristor as an over voltage protection? Wonder what the voltage rails were at?
@@thetechgenie7374 I forget but I believe they were quite high. I was unwilling to run it for too long to troubleshoot in case something was heating up. Last thing I want is a cascade of failed components due to overvoltage!
@@chongli297Yep so the SCR definitely doing it’s job don’t run it. I definitely suspect the preregulator and DC-DC converter frequencies may be off. They have to be very close otherwise throws off regulation and you have voltages way too high. Plus you get noise on both channels if scope was running when without SCR. Something definitely not right and person that had it disabled protection and took the shortcut to get it working.
