Electronics > Repair

Scope CRT tube blury till warmed up - can it be repaired

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Swake:
Hi,

Before buying a Hameg scope I would like to receive your advice about the possibility to repair it.
The CRT tube is blurry when the scope is just switched on and 'cold'. Ones warmed up, after about 20 minutes, the blurriness disappears.
Is this generally repairable or more a sign of a near dead tube?

Gyro:
20 minutes is a bit long for the CRT itself. It's also encouraging that the trace comes into focus rather drifting out. It could be aging resistors in the high voltage resistor chain that includes the focus control, astig etc.

You didn't mention the model number, you should check that the manual and schematic are available on the web - I think most Hamegs are, but check.

Swake:
Thanks for the reply.
I don't know the exact model yet. The person reported it as a 1GHz scope and purchased around the century change. So I guess it is about 20 year old. Couldn't find a 1 GHz Hameg scope from that era... So now I'm curious :o
Monday I'll see the scope in person and we'll know.

Gyro:
No, Hameg were more were more mid range, I don't think they ever made anything much above a few hundred MHz. Tread carefully, make sure of what you're getting and that you're not paying through the nose for it - try to at least get a model number out of the seller beforehand so that you can do your background checks.

james_s:
I's possible that it's the tube, but I would be more inclined to suspect the focus voltage or something else related is drifting.

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