[sdiy] Cheetah MS800 replacing NiCd Varta Mempac

Brian Willoughby brianw at audiobanshee.com
Fri Jun 4 05:26:14 CEST 2021


Speaking of the spec, do you have a spec for the Varta Mempac? The data sheet might have such details as the maximum recommended trickle-charge current. If you can find specs, you can work backwards from those to see whether it's compatible with the Cheetach MS800 circuit.

As for replacement with a coin cell holder, I've had bad experience with that. Every used synth that I've purchased needs to have the coin cell replaced very frequently. In contrast, the same CR3032 soldered onto the board performs a lot better than a CR2032 in a holder.

In contrast, I have no experience replacing a NiCd with a CR2032. Given the risk of battery acid damage, I suppose there might be a good tradeoff to be made. I've never had a soldered CR2032 leak, so I always replace them with a soldered model after they expire. The rechargeable are admittedly a different story.

Brian


On Jun 3, 2021, at 08:51, Joel B wrote:
> Not sure if still possible but I was able to find a company selling replacement nicads that looked like they matched the spec of my cheetah MS6 back in 2016… didn’t want to remove the charging system: 
> 
> This is from my receipt:
> 
> 3.6V 110MAH NICD
> Item# NIC0010
> https://interstatebatteries.com/
> 
> Worked for me.
> 
> Joel
> 
> On Jun 3, 2021, at 8:10 AM, Mike Bryant wrote:
>> I've always dropped in NiMH into NiCad slots okay.  But that's no guarantee.  As you say not getting rid of the old one is a far worse scenario.
>> 
>> -----Original Message-----
>> From: Richie Burnett
>> Sent: 03 June 2021 15:30
>> 
>> 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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