Scope repairs

List, Christopher Chris.List at sc.siemens.com
Mon Nov 29 21:31:15 CET 1999


I have a similar model scope (2213A, I believe), and had the exact same
problem. 
I posted my question on Usenet (sci.electronics.equipment or some such) and
got the following reply:

<paraphrase>
There is a bank of 6 or 8 hi-wattage 220K resistors on the main board that
control the focus of the CRT (I think they're in the CRT amp section). They
good bad over time, replace them with 1% metal film version and it should be
good as new.
</paraphrase>

...I did as instructed and sure enough, the focus was fixed. I forget the
wattage - either 1 or 2 watts. The replacements I got are about twice the
size of a 1/4 watt.

Regardless, I doubt very highly that the CRT is to blame.

Check it out on the schems and see if you can find these resistors - if so
replace them.

Note that I had a hell of a time with some of the torx bolts that hold the
cover on. Those are about the stupidest pieces of hardware I've ever seen.
The small ones have almost nothing for the tool to hold on to, and they
strip very easily.

- CList


-----Original Message-----
From: Paul Perry [mailto:pfperry at melbpc.org.au]
Sent: Monday, November 29, 1999 2:57 PM
To: synth-diy at mailhost.bpa.nl
Subject: RE: Scope repairs


At 01:37 PM 29/11/99 -0500, Caloroso, Michael E wrote:

>Sounds like a dying CRT, either the electron guns or the deflectors have
developed a fault.  There might be a problem with the driver circuits, but
that's less likely.
>
It doesn't sound anything like it to me.
If it deteriorated over a day or so, it sounds like a
capacitor, somewhere in the focussing/beam forming ckt.

paul perry melb australia



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