HP 71b repair advice - won't power on with batteries or on AC adaptor

[dmh]

I have 2 plastic backed 71b units with battery terminal corrosion and breakage, one bad and one worse. They won't power on with batteries and I was hoping they would work on the AC adaptor but no go with that either (I tested a working 71b without batteries on the same adaptor so the adaptor is fine).

Other than the battery terminal corrosion they look in reasonable condition and keyboards feel ok.

I haven't been able to locate much information on what to look for or try in this situation (I found some reset articles but the problem unit in these was powering up but freezing and mine don't power up at all).

How hard is it to take the 71b (plastic back) apart and then are there any easy test/fix points?

Could it just be the AC adaptor connection is corroded too or is it more likely to have damaged something else first?

Has anyone had much luck repairing the 71b?

TIA, dmh