I have this evening been tackling the other 7A26 and it had also been twiddled and this time one of the DC balance pots had been moved so far off that the gain could not be set at all. The clue was that the manual warns you that they interact. The DC balance affects gain mostly.
On this plugin the twiddler had used a different tool to swap the chips around and all the legs are bent
I am now ready to finish off calibration and then it is sort out the graticule lamps and intermittent power switch and the electrics will be complete.
The only real fault was that FET in the timebase and the rest has just been twiddler related apart from dirty switches.
It was FOC with faults.
I am pretty sure it was "knocked up" from a load of faulty bits.
The search for something to replace the bottom panel and heat sink cover can now begin.
I have even made up a cable to compare two plug ins for calibrating one with another newly calibrated example. It will be a lot quicker than that a bench PSU and meter like I used on the first one.
As it is to be used as a main bench scope the cosmetically challenged side panels can stay as they are as the other equipment either side will hide it from view.