Amstrad PCW 8256 focus adjustment

[gertk]

Just acquired two Schneider Joyce aka Amstrad PCW 8256 fixed the floppy drives with new belts and they seem to work fine except one of the screens is a bit out of focus.
Alas there seems to be no focus adjustment potmeter. I did find a service manual PDF but is quite unreadable.
Any ideas on how to adjust the focus?

 

[gertk]

Small update:

Having found a better schematic it seems there is no focus adjustment provided..

The CRT has pin 7 (focus) tied to +100V with a 33k resistor. I tried with different voltages to this CRT pin but it does not react to it at all, either at zero volts or +100 or even lifting it to +125 Volt, the focus does not change. Perhaps this CRT does not have this pin internally connected.

The other grid pin (pin 6) is also connected to +100V through a 33k resistor and if I vary the voltage on this pin only the brightness changes but no difference to focus.

So all in all my guess is there is no focus improvement possible with this Orion 340AXB31 CRT. Note it is not bad and certainly usable, just a tad bit off probably due to age/wear.

 

[Chuck(G)]

Perhaps the Joyce uses magnetic focusing. There should be an adjustment on the yoke assembly if so.

It's been years since I parted with mine, so I can't verify anything. (FWIW, it was sold by Sears in the US somewhat unsuccessfully, so mine was 120V 60Hz).

 

[gertk]

Perhaps the Joyce uses magnetic focusing. There should be an adjustment on the yoke assembly if so.

It's been years since I parted with mine, so I can't verify anything. (FWIW, it was sold by Sears in the US somewhat unsuccessfully, so mine was 120V 60Hz).

The only adjustments on the yoke are two 'rings with a tab' and the clamp holding the yoke in place. If I look at the green glue they have not been tampered with nor has the yoke 'drifted'. In my experience these are for positioning and adjusting the geometry of the complete image. Geometry and position are ok.

 

[Chuck(G)]

No, that's not magnetic focus then. Keep checking out the electronics then. You said you had a better schematic?

 

[gertk]

No, that's not magnetic focus then. Keep checking out the electronics then. You said you had a better schematic?

This is a piece of the CRT circuit, pin 7 should be focus but no reaction to change of voltage, pin 6 voltage only alters the brightness.
Both pin 6 and 7 are fixed at a measured 100 Volts DC.

The tube is an Orion 340AXB31 it is connected through PCB003 on the right.