Focus on Tek 2236 Scope
 

On Tue, 10 Aug 2004 17:33:58 -0700, "Michael Melland"
wrote:

IIRC there are 5ea 1/2 watt 1meg or 510K (value depends on scope model)
Ohm carbon resistors in there as a focus string that age and get flakey that
very often causes this problem. They are in a row by the focus pot on the
main board..... check those and replace if off value or open. I had a 2235
with the same problem once .... Jim Yanik, an ex Tek employee gave me this
info and it fixed mine.

That said...BE CAREFUL in a scope..... HIGH VOLTAGE present.... 20,000
volts. Don't go inside unless you know what you are doing.

Mike, W9WIS


I see the 510Ks in the circuit diagram, so this seems like a good place
to start looking. Thanks for the tip.

I've worked on HV stuff before, so I think I can avoid killing myself.

Hi Rex,

No problem on the tip.... I suspect others would have chimed in if I didn't.

These days I always feel I need to add the HV disclaimer grin.... seems
most people rarely see more then 12 vdc these days grin.

Mike, W9WIS

In article , lid
says...


On Tue, 10 Aug 2004 17:33:58 -0700, "Michael Melland"
wrote:

IIRC there are 5ea 1/2 watt 1meg or 510K (value depends on scope model)
Ohm carbon resistors in there as a focus string that age and get flakey that
very often causes this problem. They are in a row by the focus pot on the
main board..... check those and replace if off value or open. I had a 2235
with the same problem once .... Jim Yanik, an ex Tek employee gave me this
info and it fixed mine.

That said...BE CAREFUL in a scope..... HIGH VOLTAGE present.... 20,000
volts. Don't go inside unless you know what you are doing.

Mike, W9WIS


I see the 510Ks in the circuit diagram, so this seems like a good place
to start looking. Thanks for the tip.

I've worked on HV stuff before, so I think I can avoid killing myself.

Can I have your scope if you do.



--

On Thu, 12 Aug 2004 17:07:24 -0500, Dennis
wrote:

I've worked on HV stuff before, so I think I can avoid killing myself.

Can I have your scope if you do.


Sure. I'll email you if it kills me.

On Wed, 11 Aug 2004 19:30:01 GMT, Rex wrote:

On Tue, 10 Aug 2004 17:33:58 -0700, "Michael Melland"
wrote:

IIRC there are 5ea 1/2 watt 1meg or 510K (value depends on scope model)
Ohm carbon resistors in there as a focus string that age and get flakey that
very often causes this problem. They are in a row by the focus pot on the
main board..... check those and replace if off value or open. I had a 2235
with the same problem once .... Jim Yanik, an ex Tek employee gave me this
info and it fixed mine.

That said...BE CAREFUL in a scope..... HIGH VOLTAGE present.... 20,000
volts. Don't go inside unless you know what you are doing.

Mike, W9WIS


I see the 510Ks in the circuit diagram, so this seems like a good place
to start looking. Thanks for the tip.

I've worked on HV stuff before, so I think I can avoid killing myself.


I just thought I would follow up on the status. I finally found the time
to dig down to these resistors. A bit of a pain getting to them, but not
horrible. I replaced them all (there were 6 of them in the string) and
now focus is great again.

Found one of the 510 K's had become well over a meg.

Thanks for the great tip on what to check.

-Rex, KK6MK

No problem Rex..... glad to have been able to help.

Mike

--
Michael Melland, W9WIS
Winneconne, WI USA
http://webpages.charter.net/w9wis