32-bit acorn hardware • Re: The AKF18

What I cannot find is how to make the change. I have reviewed the schematics over and over and I think I know how to solve it, but when we''re dealing with 26,000V (per the CRT) I'd kinda like to make sure.

Does anyone know how to make the switch??

Hi Matt,

Looking at the schematic, and the board of an AKF18 on my bench I'd say that the points being labelled as '240v' and '110v' on the board is rather confusing: The non-existent "S308" switch from the Commodore 1960 monitor essentially shorts them together when set to "115v" according to the service manual... (If you look at the PCB photos here https://www.nightfallcrew.com/19/10/201 ... 960-boxed/ you will see that it really is the same monitor)

The voltage selector on other SMPSUs is often configured in as similar way - essentially tying Neutral to a point in the middle of a pair of mains filter capacitors.

So I think with a reasonable amount of certainty, you should be able to wire a link between the circle marked 240v just next to TP15 which is between the positive leg of C809 and the negative leg of C808, and the circle marked 110v which is next to TP17 and connects to a leg of C805.

Regarding the EHT voltage - so long as you are not planning to discharge the anode cap, which is not necessary for this modification then you needn't worry too much about that.
Please do bear in mind however that you are dealing with the non-isolated mains input side of the PSU so it would be wise to ensure that there's no residual charge held in C808 / C809 as these could give you quite a hefty belt (usually only in the case that the PSU isn't starting up due to a fault, but let's not chance it!). In theory the parallel resistors R802 and R803 (each 120K) should bleed those capacitors to avoid this scenario but I'd short them to ground before touching them just to be on the safe side.

I'm pretty sure this is correct but if it's wrong then the most likely outcome would be the PSU simply not starting up.

Please do write back to let us know if this worked

Please also ensure that you permanently mark/label the rear of the monitor to indicate that it's been modified to 110V just in case some poor devil tries it on 240v in the future

Best Regards
Jonathan

Statistics: Posted by PJTech — Tue May 06, 2025 11:16 pm

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