Fried my RS-110 filter with reversed polarity

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talkboxert
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Fried my RS-110 filter with reversed polarity

Post by talkboxert » Sun May 19, 2019 7:11 am

Ok. In 15 years of modular it had to happen at some point.

I reversed the polarity on my Analog Systems RS-110. :bang:

With so many good filters out there it's kind of useless €-wise to bring this to a professional tech (I'm no solder guy)

I was just wondering if there are any usual suspects for instance in the IC's that I could try to replace. A friend of mine has some soldering experience so we could also do some simple component replacement, but there is no public schematic as I know of.

Any tips on bringing this back to life are more than welcome!

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GilgaFrank
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Post by GilgaFrank » Sun May 19, 2019 10:48 am

You may be able to repair it with no soldering. Chances are you've damaged the opamp/OTA IC's so you may find you can simply replace them in the sockets. Get an IC extraction tool

https://www.bitsbox.co.uk/index.php?mai ... ts_id=3315

And a pin straightener

https://www.ebay.co.uk/itm/IC-STRAIGHTE ... XQh8NTchPD

Note that there is an indentation at the top of each IC which indicates the correct orientation when replacing them. Replacements should be readily available on enay for the IC's.

You may also have damaged the electrolytic capacitors next to the power header. These would require soldering to replace them but you can easily read the values and rating and order new ones. Again, these are polarised components so they must be inserted the right way round so take photos before removing the original capacitors and check here before resoldering. I'm confident anyone with basic skills, tools and patience could get that module working again.

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ranix
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Post by ranix » Sun May 19, 2019 11:33 am

take a look at all the ICs with a good bright light and look for any signs of heat damage or bubbling plastic or scorches around the feet

if you find one, chances are it's your only damaged component

I'd say like 3 times out of 5 there will be damage visible to the naked eye

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appliancide
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Post by appliancide » Sun May 19, 2019 1:05 pm

I fixed a broken ASys filter for someone about 5 years ago. The owner claims that it wasn't plugged in backwards, but not sure what else could have damaged it :hmm:

Anyway, I recall having to replace a few of the transistors. I also swapped out the tantalum caps (maybe as a precaution, just in case the owner didn't damage it by plugging it in incorrectly). I don't think that it was a 110 though, so there's probably some circuit differences. Sorry I can't remember exact details, but just wanted to point out that, on that particular design, it wasn't just ICs that were damaged.

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GilgaFrank
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Post by GilgaFrank » Thu May 23, 2019 1:04 pm

Yeah, you're fucking welcome. Don't mention it.

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talkboxert
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Post by talkboxert » Mon Jul 29, 2019 2:56 pm

Hi there, some nasty health issues kicked in after my first post, and have taken me out of everyday life for quite some time. :deadbanana: so hence the silence on my part, my sincere apologies.

Just wanted to thank everyone for providing these tips, I hope to be back in the studio in the next few weeks so I can put them to use. Cheers!

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Bartimaeus
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Post by Bartimaeus » Mon Jul 29, 2019 10:53 pm

In my experience, the tantalum caps are the first things to go in ASys modules when they're plugged in backwards. I'd try swapping those out, then work upwards from there.



Also, that's crazy harsh, gilgafrank! We're just trying to help people out here, no need to be so self-centered and offended. It's pretty common for threads to die when life stuff comes up, give the benefit of the doubt.

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talkboxert
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Post by talkboxert » Sat Sep 21, 2019 8:03 am

Hey there! Finally got around to getting some work done on the RS-110.
Thanks to all the tips here I swapped out the tantalum capacitors. Also just to be sure I swapped all IC's (TL072 & CA3080) except the CA3086, wich according to a guy on the Dutch synth forum probably survived the reverse polarity.

When firing up the filter I was happy to hear signal is flowing through both inputs, resonance seems ok and self oscillation works. Still the overall voltage situation seems quite out of balance. The cutoff closes too early (before it's full ccw) and doesn't seem to reach full value at max cw setting. I can push it to the max with external cv (more than 5v is necessary). Also the V/oct tracking is completely off. The onboard trimmers don't have enough range to solve these issues, so something else must be wrong.

Just wondering as a starting point, could it be I picked the wrong capacitors to start with? They are polarised tantalum capacitors with exactly the same rating but they have a 20% tolerance, could this be what's causing the problem? I don't know the tolerance of the original ones, but they are also significantly smaller. Does size matter in this case (and tolerance)?

Cheers

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Post by tarandfeathers » Sat Sep 21, 2019 8:32 am

The two tantalums are across the power rails and do not affect the circuit operation in a way that would cause what you're describing.

The CA3086 is almost certainly being used in the exponential converter so is directly related to the frequency tracking of the module, and the rail to rail voltages in the module are easily enough to exceed the maximum ratings listed in the CA3046 datasheet so, without a schematic to work from you don't know how it might have ended up connected, I would start by replacing that in case something in it is damaged.
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