Need help repairing couple 'scopes (different faults)

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well what i'we been told is that primary is on the ''live'' side of transformer, and secondary is on the ''isolated''.
 
Fez...you have it wrong.....

Remember 320VDC across the Main Smoothing Cap....ON THE PRIMARY.....of a SMPS

Leave it alone now. You are making me tired

Regards,
tvtech
 
fezder said:
well what i'we been told is that primary is on the ''live'' side of transformer, and secondary is on the ''isolated''.
Click to expand...

Fez

I have infinite patience with the right information.

I doubt this is even SMPS...I believe it's a Linear Supply.....

Now, as your friend, I am chasing you away so you can sit and think.
Read all I have posted and think.

I will still help you in the Morning. Not now.

Regards,
tvtech
 
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tvtech I have read through this thread once or twice now..... No-one has said it was a SMPS..

Going off the size of the thing it is most likley not to have a switched power supply...
 
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

 
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Hello Fezder!

Did you succeed on getting the service manual?

If you put your oscilloscope brand and models we could help you with that
 
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.
 
Hi Fez

Please take nice clear photo's of the Power Supply of the Scope and post them. We can go from there

All the best,
tvtech
 
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

 
Thanks Fez

Please tell me if you see a normal Mains Transformer anywhere there while you have the casing open...

Regards,
tvtech
 
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

 
OK....I understand now.

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.

Regards,
tvtech
 
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
 
Heya Fez

OK. Which Scope did you fix??
So many different ones and all.

Regards,
tvech
 
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