Laserjet 5 error - install printer cartridge

[mcpwin2k2002]

I think the High Voltage power supply may be going/gone bad. Can anyone tell me how to test this?

[Placebo]

If you havn't already try another toner. If you have then make sure the contacts on the HVPS that the toner comes in contact with are clean and are not stuck down to where they cannot make contact.