There are several versios of the HP9845. The 9845A is very differnet to the 9845B. The 9845B anmd 9845C (colour) are similar apart from the monitor section (which includes a lot of digitial circuitry, jsut to keep you on your toes...) I beelvie the PSU come in sevearl version too, and that 9845Bs wit hthe 'high speed language processor' have a different PSU to normal ones. You can get my schematics for the 9845B from the Australian site, but of course they only cover the machine I've got -- a 9845B with high speed language processoar and enhanced monochrome nonitor. With that in mid... The easiest place to check the mains wiring is on the barrier stip of faston terminals on the side of the PSU casing. There are 4 connections there, iot may look like more, but theuy common together internally. All the wires of the same colour are linked. Numbering the tags with 1 at the top and 4 at the bottom, and assuming the votlage selector is set to 230V: Between 2 (White/.Red/Geey) and 3 (Grey) you should see full mains voltage Between 1 (White/Green/Grey) and 2 (white/Red/Grey) you should see half mains voltage Btween 3 (Grey) and 4 (white/Yellow/Grey) you should, again, see half mains voltage. The cooling fans are 120V AC units. The left hand one is conencted between tags 1 and 2. The right hand one is conencted between tages 3 and 4. The internal circuitry of the PSU include asmall mains transformer used ot power the chopper cotnrol circuitry. With the selector set ot 230V, the priomary of this transformer also acts as an autotransformwer to split the maisn in ahlf for the fans. Are the fans running? If so, then the mains input is almost certainly correct. This power supply is complicated -- very. The one I have is on 5 circuit boards, in contains 17 ICs and has 4 chopepr transistors. Take care! What was the problem with the monitor? -tony