Posts: 260
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Joined: Jul 2005
I don't know if it is related to you problem, but have you read this article?
http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=267
It somehow excludes the HP-29C, stating that it has different problems, but maybe it helps?
Posts: 441
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Joined: Apr 2008
The only similar unit is the 25C which uses (usually) only one of the same rams as the 29C. Other than that one ram IC, the other logic parts are different although the display parts are the same.
If you get a display of any kind, chances are very good the power supply is fine. The 0.00 display says the ACT is probably okay as well so I'd be focused on a rom or ram problem.
If there is any corrosion at all on the board, you'll need to remove it. Depending upon the severity, either remove the IC's and clean or soak the board standing on end in vinegar followed by a warm water wash and dry afterwards. The roms are the three 8 pin dips units along the left side, the two 14 pins on the right are the rams. The 8 pin above the ACT is a power up reset IC.