Re: 25C needs to be warm for registers to work Message #2 Posted by Vieira, Luiz C. (Brazil) on 13 Feb 2005, 5:06 a.m., in response to message #1 by Gordon
Hi, Gordon;
what I can take from your text is that some "cold soldering" is the cause. When gets warm, all metal (exceptions?) dilates. I'd search for a Vcc (Vdd?) terminal in the RAM IC that's probably wiht a bad contact and, when warmt, extends enough to contact with the board. These are mainly the edge-positioned terminals. I had an HP25 with this problem, ie. no way to keep information in RAM. In my case it was a bad RAM because I resoldered and tested it in another unit.
The HP25C has a single RAM that's continuously fed for as long as the batteries are installed and with enough charge. I saw some units with a provision for another IC, but I never saw an HP25/25C with two RAM IC's.
What bothers me is the fact that the 1Watt resistor (current limit), that's mostly the one that heats up, is in the opposite side of the RAM IC; in fact, it is closer to the second ROM and the ACT. Maybe, just maybe, you have a broken copper trail close to the 1W resistor that connects after getting warm.
Not much of a help, I guess you have figue it all out, but I could not help posting.
Cheers. And success!
Luiz (Brazil)
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