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Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
this is why i'm confused too, as i can't even locate anything that would show SMPS, apart from crt flyback drive of course (haven't touched that thing...)
well now i lied bit, i did touch flyback drive, but only it's cover to see if there would be that smoother cap, but no luck there.....those caps seen before are biggest caps physically in entire system, but you meant size about say, computer psu caps/similar rated around 320-450v?
see these photos to see better what we're dealing with
sure, i managed to fetch service manual, well actaully only i'we found were block diagram and circuit schematics, pretty confusing gotta admit.
the current one is kikusui cos5040, got total of 3 malfuntioning....
seems i cant insert pdf as file....
ok, little more testing, seems it can draw something, test signal from probe calibration point comes okay, but it sweeps only once per ssecond about, and then disappears, like when time/div is low.
took some time, had to disconnect and desolder connections to take better shots, but here, that looks like PSU section to my eye, and it matches schematics of PSU.
that burnt mark at pcb on last photo is where used to 4.7k resistor, i piggypacked it along its pair and secured it with zip-tie, just to make sure that fault doesn't occur again
oh yes, there is, it isn't mounted anywhere on pcb, instead its bolted on back panel, and wired from there, see photos. This model has 4 different mains voltage settings that's why bit mess with wires going around transformer...
that other photo just shows portion next to flyback transformer and some hv caps next to it, dunno if it's useful
It's not SMPS....that is why you got lost with the whole discussion last night...that is why you could not understand what I was on about
And you could not locate the Main Smoothing Cap....because there isn't one
Sorry for stuffing you around...Photo's help though like the one's you posted just now.
Leave the Scopes for now...close the cover/s and put them somewhere safe. For another Day.
now then, i checked another scope, which seemed to have PSU problem, it draws way too much current even on its own, around 0.5amp idle. I took it completely apart from scope itself. After long inspection, i noticed nothing broken, but i changed some browned diodes and bulgy-looking caps. but, the main reason that causes s/c is one screw that is for connecting pcb to ground, as it punctures one of pcb tracks, causing some small sparks fly.....seems there is some sort of isolation missing between pcb/ground, as it has left burnt marks on case! funny thing is, i haven't taken this pcb out before.
there are numerous regulators also in case, 4 of 5 are isolated by mica and plastic standoffs, and read ok by output, but the last one lm317. adjust knob doesnt help.
Now then, when falut occurs lm317's input voltage drops to around 1.3v.
any clues? lm317 seems to be intact even out of pcb, i mean no s/c or o/c
managed to track what that S/C shorts out. There is one pair of series connected windings. The screw connects 0 potential and other end, so other pair of this series connected is shorted when screw is tightened.
no wonder transformer get hot and hums loudly.....but still, current isn't enought to blow fuse, as fuse is 1A
psu section is now repaired, all voltages are in order. There were 2 shorts via screws, and one broken pcb track. No signal yet on screen, no matter how i wiggle knobs
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