HP-25 not working

[Hiwi]

Check the current, it should be 160-180 mA when turned on, ok only with display, but if it is zero, there can be a contact problem. Then check voltages VGG VDD and VSS. You can find schematics in the net. I recently fixed a 25C which has no continuous memory. There was the typical problem with corrosion. The Pwon line was interupted under the memory chip. So if turned off, the memory had no battery on Pin 1.

In most cases, when users plug in the charger without battery the ACT Chip could be damaged, so there is often a 0.00 or flashing numbers on the display. (No keyboard action) If there is nothing on the display this could be a faulty Cathode /Anode driver.

Ralf