Tektronix 2230 - no readout


Hi guys,

my first post here.

I have been given a Tektronix 2230 scope.
The previuos owner could remember het go it from somebody else, and there was something about a fuzzy readout.

I always find it a challenge to repair electronic equipment, but this time I am stuck.
The scope is very clean and probably not used very much, if it ever has been used. Or if it has even worked as it should be.
Inside there is no dust, and no repairs have been done previously.
The GPIB option board is present, as well as the memory option. The backup battery is OK.

(please take a look at the video) / https://www.youtube.com/watch?v=8YkXAwB-x4Y&feature=youtu.be

On startup, the analog function looks OK, all the controls are functional. Tested when rest jumper is set.
(Except for an issue with the attenuator which looks to be open in some positions, bad contact?).
After some time, after 40" in the video, the analog screen disappears completely.
When you push beamfind, there is some small rectangular image somewhere, this can be top or bottom, an left or right.
After some time, after 1:20" in the video, things start to change. While pushing beamfind, it looks like some diagnostic things are displayed, but you cannot recognize any text.
So, the fuzzy readout the previuos owner saw was this behaviour.
Pushing the select on the cursor pot or turning it has no effect.

I have a nice service manual (Artek Media).
I must admit it is not very clear to me.

I have tested and measured all sort of things, but there is nothing that looks not normal at first sight.
Voltages are OK, also the plus and minus 15V on the vector board. I have forgotten to measure the 5V ref.
There are no leaking or thick capacitors in the PSU (Why do they make is so difficult to remove te cover?)
Data- and addresslines do not show unlogical signals, ie. shorts between addressline or outputs behaving strange. Tested real-time, and in testmode.
Clock 40MHz and 7.66MHz are OK.
Changed the processor (recovered from a very old Epson XT PC), no change.
Checked the display controller socket, but nothing unusual. The controller heatsink itself is touchable, so no overheating.
The digital push buttons are electrically OK, also the cursor pot (checked with ather scope). No of them seems to be doing something.

From the video, and monitoring addresslines, it seems the processor is running, but maybe it encounters some sort of error.
I have no experience with (digital) Tek scopes. Perhaps I am overlooking something simple.
Anybody has a clue?

Thanks in advance, Harry from Belgium

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