DM15L loses memory contents

Discussion of hardware issues related to the DM1x/DM41. Please ensure that you specifiy whether the issue is related to a credit card size unit or a "Voyager" unit (DM1xL/DM41L).
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ultrarunner
Posts: 1
Joined: Sat Jun 22, 2019 5:35 am

DM15L loses memory contents

Post by ultrarunner »

My DM15L (S/N 482) has recently developed a little problem: About once per week it loses all memory contents and settings when powered on. Two interesting facts: When this happens …
  • … it does not show "Pr Error".
  • … it reverts to the default font (which it doesn't do when manually reset by "ON + minus")
The battery voltage is 2,49 V, and no battery warning is displayed. The RTC is not affected. A firmware update from V26 to V29 did not help.
Has someone any idea what could be the reason for that behaviour?
grsbanks
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Joined: Tue Apr 25, 2017 11:23 am
Location: Preston, Lancs, UK
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Re: DM15L loses memory contents

Post by grsbanks »

Interesting.

It could still be the battery if it's a cheaper brand. One way to find out is either to replace it anyway, they're not expensive, or to switch the calculator CPU clock to 12 MHz instead of 48 MHz ([ON]+[9] key combo). It will reduce overall battery drain and maybe prevent the supply dropping below the threshold that might be causing this.

Cheaper batteries tend to have a higher internal resistance than batteries from a good brand, which means that the voltage delivered by them drops more when under load than it would with a better battery.

If it's still the original battery that came with the calculator then it's probably a Panasonic, which is good, but it means the problem is elsewhere...
There are only 10 kinds of people in the world: those who understand binary and those who do not.
Yordan
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Joined: Wed Apr 22, 2020 10:28 am

Re: DM15L loses memory contents

Post by Yordan »

How is the memory content maintained between the modes? Is it always stored in RAM, or it is mirrored in some kind of Flash by power off or some other event? Could it be that the write cycles of flash memory are exceeded? (If you put automatic mem copy to Flash every minute or something, then in two operational years the write cycles of the chip are exceeded).
grsbanks
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Joined: Tue Apr 25, 2017 11:23 am
Location: Preston, Lancs, UK
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Re: DM15L loses memory contents

Post by grsbanks »

Everything (except the time, that's in its own RTC chip) is stored in the on-chip SRAM in the CPU.
There are only 10 kinds of people in the world: those who understand binary and those who do not.
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