[sdiy] Cheetah MS800 replacing NiCd Varta Mempac

Tom Wiltshire tom at electricdruid.net
Sat Jun 5 11:24:39 CEST 2021


I don’t know about the MS800, but the Polysix has a “tape dump” feature for the memory, so you can save the patches (these days to an audio file rather than a tape) and then change the battery and put them back afterwards.
If the MS800 doesn’t have anything like that, then I agree it’s going to be trickier to change the battery without losing the patches.

==================
       Electric Druid
Synth & Stompbox DIY
==================



> On 4 Jun 2021, at 16:53, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
> 
> Hi Tom,
> 
> I've read about this suggestion of fitting a CR2032 battery instead, and I know that some of the synths that came a bit later like Casio and Korg used these batteries instead for memory backup duty.  The thing that concerns me about this is that it is quite a departure from how the original Cheetah was designed to work.  The battery voltage is lower, and the charging needs to be disabled.  It is also not clear how the user would go about changing this battery in the future without risking loosing data.  I guess they would need to bridge the CR2032 battery holder with another external voltage source whilst taking out the old battery and inserting the new one?  This sounds like something a technician would have to perform in order to guarantee no loss of data!
> 
> -Richie,
> 
> 
> -----Original Message----- From: Tom Wiltshire
> Sent: Thursday, June 3, 2021 4:25 PM
> To: rburnett at richieburnett.co.uk Burnett
> Cc: synth-diy mailing list
> Subject: Re: [sdiy] Cheetah MS800 replacing NiCd Varta Mempac
> 
> On the Polysixes I’ve worked on, I always replaced the NiCd with a coincell battery holder. The diode that provides charging just gets removed.
> 
> Then you can just stick a new watch battery in it every five/ten/whatever years.
> 
> Tom
> 
> ==================
>      Electric Druid
> Synth & Stompbox DIY
> ==================
> 
> 
> 
>> On 3 Jun 2021, at 15:29, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
>> 
>> Hi all,
>> 
>> I'm currently servicing a Cheetah MS800 digital wavetable synth and want to change the old NiCd Varta Mempac to a brand new NiMH Varta Mempac before putting it up for sale.
>> 
>> The old blue NiCd battery hasn't started to leak yet, and is still holding it's charge but I know that old NiCd Mempacs are regarded as a ticking time-bomb in equipment of this age (>.<)  I wouldn't feel comfortable selling it without addressing this issue first.
>> 
>> The existing 100mA 3.6V NiCd trickle charges from the 5V supply rail through a 1k resistor when the unit is powered up.  Should I be looking at changing this trickle charge current when changing the battery type to the 150mA 3.6V NiMH replacement?
>> 
>> I did a search online and found very little solid information about this. Everything from "The NiMH Mempacs are a drop in replacement" to "you need to decrease the trickle charge current because NiMH is less tolerant of being overcharged"  The trickle charge current already seems low to me.
>> 
>> I would be interested to hear your thoughts!
>> 
>> -Richie,
>> 
>> -- 
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> 
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