HP27 Restoration (Lots of Corrosion)

[calc-calcs]

Well my ACT seems to have died, it will no longer boot as it was doing quite often before, and according to Bernhard this is a typical scenario when damaged by overvoltage it can work for a while and then just quit. He also explained that the HP27 uses RAM for the operations that are not working in my machine (Trig, Financial, 1/x, etc) so the RAM memory inside the RAM/ROM chip is definitively bad and of course it is an unobtainable part. I already had a suspicion of the RAM problem due to the storage registers and the E+ function not working and always returning zero.

Something similar happen to me with the RAM chip of the first HP25 that I restored, it had some corrosion on the bottom of the chips which I cleaned, but it seems it can leach into the chips (probably trough the pins) and cause internal damage. In that machine RAM was initially working but after a few days sometimes would work sometimes it would not, and then finally died. Of course never was able to get a replacement RAM chip either, so that HP25 ended up with the Panamatik ACT.

Unfortunately I think this is the end of the line for the HP27 attempt to make it work with its original hardware, so I placed an order for another ACT that will be specifically configured to interface with the HP27 motherboard, and that should take care of all the remaining issues. If for any reason that ends up not working due to problems with the motherboard, I still would have the option to reconfigure the ACT to work on one of my HP21 motherboards, and use it to make the HP27 operational. Bernhard explained that I would only need to add pin 12 to the ACT, and add a wire connection and of course reload the proper firmware. It would be a bit of a cheating restoration, but I do not know of any other alternative if the original motherboard keeps giving me grief.

Thank you everyone that made suggestions and provided information. Stay tuned and I will be updating this thread once the newly ordered ACT arrives in 10-15 days.