Roland Promars (or Jupiter 4) envelope & modulation issues

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caro
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Roland Promars (or Jupiter 4) envelope & modulation issues

Post by caro » Sat Jul 25, 2020 4:17 pm

Hi everyone,

I have recently bought a defective Roland Promars synth which apparently has experienced a battery leak. The corrosion has affected some parts of the motherboard, but I have managed to wash the board to prevent it from further damage. The synth powers up fine, but there is an issue with the VCA & VCF envelope generators which do not work properly – the A D R potentiometers do not affect sound at all (only the S works on both VCA & VCF). The Release of both VCA & VCF envelopes is short even on all the preset sounds.

In addition the VCO MOD & VCF MOD sliders do not respond at all. Currently the modulation is "stuck" on the VCO and the VCO MOD slider doesn't change the amount of the modulation.

The schematics show that there is a multiplexer IC (CD4051BCN) located on the motherboard (IC 6) which scans A D R settings of VCO and VCA and the VCO MOD and VCF MOD settings. I have replaced that chip to an equivalent (CD4051BE) but it didn't help at all.

I wonder if any of you have encountered similar problems with Promars or Jupiter 4 (as they share the same main boards) and could share any info and ideas where I should look further…

Thank you!

caro
Newbie
Newbie
Posts: 5
Joined: Fri May 21, 2010 2:39 pm

Re: Roland Promars (or Jupiter 4) envelope & modulation issues

Post by caro » Tue Jul 28, 2020 2:46 pm

Luckily I've found this wonderful resource https://synthronics.de/synthesizerrepar ... jupiter-4/ where the author shares his restoration process with very insightful info. Apparently there is also a demultiplexer IC (IC 31) which is connected to the same sliders, so I've replaced it as well and WOW – everything works now perfectly!

The last thing left is to replace a battery. I've bought a replacement NiCad battery from eBay which is 3.6v. Also, Syntaur sells similar 3.6v replacement batteries (https://syntaur.com/Items.php?Item=4486). However, in the schematics, it is shown that the original battery is 4N-100AAS. I've checked online and it seems to be a 4.8v battery. How can this be? Is it safe to use a 3.6v battery in the same charging circuit of the Promars?

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