HP25C repair, help needed

[albertofenini]

Dear Jbem,

that's exactly what we have done so far.

When we try to troubleshoot a machine we always attach a pack of rechargeable batteries that we charge externally, so no original battery pack nor charger here either.

We have both a multimeter and an oscilloscope but differently from the HP-65s we have recently repaired here we are missing a correct scheme so that we don't know where we can intercept the Vss, Vgg and Vdisp in the nearby of the PSU.

We know where we can get them at the pin out, but we suffer from the lackness of a PSU scheme with correspondence with physical components. The HP25 PSU is different, has more components and are connected differently.

PCB is clean, it has been checked but it has no broken traces nor oxidation whatsoever.

We will try over the weekend to test the PSU components, diodes and transistor, and we can definitely de solder the ACT and the RAM in order to see if Voltages and Current consumption are stable.

We will be more than happy to hear from anyone that may have additional suggestion, on how to check the components

Thanks again for the precious tips !