I would just put a diode in series with the + side of the Lithium-cell.
How you do it depends on where you put the Lithium-cell.
WT
----- Original Message -----
From: "jesper" <jesper@...>
To: <Simmons_Drums@yahoogroups.com>
Sent: Wednesday, December 28, 2011 10:57 AM
Subject: [Simmons Drums] MTM and change of battery
> Hi list,
>
> I thought I should change the battery of my latest MTM today. But since
> I was stupid enough not to make notes or take pictures when last time
> doing this I dug out one of the other units to have a look.
>
> No. 114 had it's battery changed by the former owner and as far as I
> remember I copied the work in my other MTM. Apart from the removal of
> the old battery and the insertion of a AA-sized Lithium dito I can only
> see one change: the lifting/removal of resistor 37. I did the same on my
> other MTM and both works well, both functions and memory.
>
> Here's a shot of what can be seen inside no. 114.
> http://www.electronic-obsession.se/studio/simmons/mtm_battery_mod.jpg
>
> So techs, let me know if this is wrong. Should I lift diode 30 too?
> Anything else? The schematics aren't the best and I'm no master at
> reading it anyway. :)
>
> Happy holidays,
> --
> electronically yours, jesper
>
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