hp28s need repair ?. Autotest fails

[tlfrance]

(02-01-2024 07:41 PM)rprosperi Wrote:  No service manual for the 28s (or any of the "Champion" folding-case models) has even been captured, or even seen, in the wild. I strongly suspect that none was ever created as the machines are effectively not serviceable, from a manufacturer's perspective; the plastic welds holding it together cannot systematically or cost-effectively be rejoined sufficient to return to a consumer for use. It was cheaper for them to simply replace the very few of these that died within the warranty period.

Sorry for the bad news.

Thanks rprosperi . I can try to repair myself the unit, and i see on pcb only few compononent (2 ROM + RAM chip ) and other discret component such as resistor, capacitors..
The difficulty is to find what is faulty. I 've searched over web for similar issue, but with no chance. But my idea is the ram chip faulty (50%). I can find it on ebay with different brand (nec or mitsubishi ) , i guess it's same ...