More Kaypro problems

I've never seen one of these PSUs, so I'm guessing here, but I've repaired enough SMPSUs in the past to give you some useful tips (it _is_ an SMPSU I take it, and not a linear...)

Remove the fuse and inspect it. You'll see one of there things : 1) The fuse is blown gently - the wire has melted, but it't not at is (2) below. In that case, replace the fuse and try again 2) The fuse has blown violently. Either the glass has cracked, or the inside of the fuse is coated in a black metal film. In that case there's a short circuit somewhere on the primary side. Likely _first_ failures are the mains bridge rectifier diodes or the chopper transistor. Alas there are normally other failures (resistors/capacitors) along with them, and unless you replace everything, your new parts will be damaged as well. 3) The fuse is fine, but the PSU won't start up. This is suprisingly common (I've had it twice in the last month). Most small SMPSUs run the control circuitry off one of the transformer outputs, which leads to a bootstrap problem (the PSU can't run without the control circuit, but the control circuit can't work without the PSU running). The solution is a small circuit to give the control circuit enough power to start. In a lot of cases this takes the form of a high-value resistor chain from the HT+ (400V DC) line to the chopper control circuitry. And for some reason this resistor open-circuits. It's worth checking all high-value resistors on the primary side. When you've inspected the fuse, get back to us and we'll attempt to talk you through the PSU... -tony