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unprogrammable HP 25
07-22-2021, 11:08 AM
Post: #1
unprogrammable HP 25
I have a 25 that appears to work normally in RUN mode but in PRGM mode when I enter a program I see the correct keycodes as I enter them but the program ends up all GTO 00 commands.

Does this mean the RAM chip is dead? Isn't it used for RUN mode arithmetic at all?

Thanks, dmh
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07-22-2021, 11:28 AM
Post: #2
RE: unprogrammable HP 25
(07-22-2021 11:08 AM)dmh Wrote:  I have a 25 that appears to work normally in RUN mode but in PRGM mode when I enter a program I see the correct keycodes as I enter them but the program ends up all GTO 00 commands.

Does this mean the RAM chip is dead? Isn't it used for RUN mode arithmetic at all?

Thanks, dmh

The HP-25 RAM chip is only used for the 49-step program storage, 8 memory locations and the Last X function memory. The stack and internal working registers are all contained within the ACT chip.
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07-22-2021, 03:21 PM
Post: #3
RE: unprogrammable HP 25
Based on Steve's reply, see if you can put anything in the storage registers (and subsequently recall it), and if the last X function works.
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07-23-2021, 01:16 PM
Post: #4
RE: unprogrammable HP 25
Ok, registers and Last X always return 0 so problem with the RAM chip - thanks :-)

Is it most likely that it needs replacing or could a clean fix it?

I haven't opened it yet but terminals look reasonable and keyboard is pretty good so not sure it's corroded.


(07-22-2021 03:21 PM)Dave Britten Wrote:  Based on Steve's reply, see if you can put anything in the storage registers (and subsequently recall it), and if the last X function works.
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07-23-2021, 02:18 PM
Post: #5
RE: unprogrammable HP 25
I'd probably start with something quick and easy: clean off and reflow the solder on the RAM chip on the off chance that you get lucky and it's just a cold/cracked joint. Also inspect the board for any broken or corroded traces leading to the chip.
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07-23-2021, 05:43 PM
Post: #6
RE: unprogrammable HP 25
(07-23-2021 02:18 PM)Dave Britten Wrote:  I'd probably start with something quick and easy: clean off and reflow the solder on the RAM chip on the off chance that you get lucky and it's just a cold/cracked joint. Also inspect the board for any broken or corroded traces leading to the chip.

If all fails, the HP-25A ACT chip will restore the RAM function.

Bernhard

That's one small step for a man - one giant leap for mankind.
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