my "new" scope died :(

[birt]

so i got my grandpas old scope. with a german manual a didn't understand.

today i switched it on.
with old tubestuff in a metal chassis like this i put my DMM on the chassis to see if it won't give me nasty surprises.

so i switched it on and after 2 second the DMM measured more than 100Vac on the chassis. before i could turn the scop of there was already light gray stinky smoke coming out of it :cry:

i haven't opend it up yet but i think it's the PT

i guess i *had* a scope...

[Paul Marossy]

Any idea how long it's been since it was last powered up? The filter caps may have fried or something because thsy were dried out or something. What model scope is it, a Tektronix by any chance?

[Regan]

I agree with Paul, filter caps. Was it sitting in an attic, garage etc? it could also have been some little animal decided to use it for a urinal- this can do damage.
Regan

[Paul Marossy]

Or perhaps there are tubes in there and one of them fried due to dust inside or something?

[birt]

it's an old Hameg HM312.
it was on an attic and has tubes in it.

but i don't have the time right now to open it and check everything. wich is a shame becaus i'm very curious to know what's wrong

[Paul Marossy]

Hmm... well, it's going to be very hard to diagnose without a schematic. I don't suppose you have one, do you?

[birt]

Hmm... well, it's going to be very hard to diagnose without a schematic. I don't suppose you have one, do you?

i do have one in the manual.


i just foudn some time to open it up and there is NOTHING that looks burnt. this makes me fear even more it's the transformer

i guess i should just desolder the transformer and test it right?
i know from the schematic it should have secondary taps for: 58V, 220V, 760V, 6,3V and 82V.

it's gonna be hard to find such a transformer

[Paul Perry (Frostwave)]

Turn it on (with the cover off) and see if the smoke is coming from anywhere obvious. May not be serious, just dust & fluff cooking on a bias resistor.
WARNING don't touch anything! think about that 800v charging a cap that is waiting for you, waiting to strike after the power is off! CROs aren't toys :shock:

[birt]

Turn it on (with the cover off) and see if the smoke is coming from anywhere obvious. May not be serious, just dust & fluff cooking on a bias resistor.
WARNING don't touch anything! think about that 800v charging a cap that is waiting for you, waiting to strike after the power is off! CROs aren't toys :shock:

can't i destroy even more if i turn it on again?? :shock:


and i know these things are dangerous, i always check everything first with my DMM

[Paul Marossy]

can't i destroy even more if i turn it on again??

Not if it is your power transformer. If so, it's already dead. If something else has failed, it's likely that the damage is already done and turning it on again won't cause any more damage. (maybe)

Umm... is there any fuses in this thing? Perhaps a fuse blew or something.

BTW, be really careful around the CRT! Some scopes have 8kV (8000V) or more on the anode of the CRT.  :shock:

[birt]

the big tube seems to work.

there was no smoke anymore.

then i measured with my dmm from the chassis of the scope to the ground pin of another mains plug (you know, from such a box with 3 mains plugs and a big on/off switch) an i still got 118Vac


and no bad fuses

[Paul Marossy]

So what does the scope do then? Do you have a CRT that lights up, but no green signal  trace shows up?

[birt]

So what does the scope do then? Do you have a CRT that lights up, but no green signal  trace shows up?

no signal trace. but is there a trace when there is no probe connected?

a friend of mine said it could be a broken elco that feeds power to the chassis. and i discovered the mains cable had no ground, it doesnt make the power go off.

so i guess i should replace the elco as well as connecting a good mains cable.

right?

[Paul Marossy]

That would be a start.