Eurorack sequencer channel 1 knobs are not affecting the cv outs

[waldenpotato]

I'm playing around with the sequencer for the first time. I'm just realizing that on channel 1 only the first step is affecting the cv outputs. Channel 2 seems to be working correctly.

For channel 1 step 1 I can control the 1v/oct input of my oscillator. But when the steps go from 2-8, the 1v/oct goes back to its base frequency as if it is unaffected by the sequencer.

What might be wrong here?


Thanks.

Update:
If this is helpful, I've just realized that channel 1 steps 2-8 do affect the cv output when step 1 is in the middle position. When step 1 is in the middle position the cv output only changes very slightly.

[Antlerface]

What sequencer are you talking about?

[waldenpotato]

The Oakley Sound Systems Eurorack Sequencer.

[Synthbuilder]

I think the resistor network RN2 is perhaps the wrong way around.

Tony

[waldenpotato]

I think the resistor network RN2 is perhaps the wrong way around.

I just checked and the dot for RN2 is in the square pad. So that looks okay.


Update:
I was looking at RN2 on the main board not the pot board. Looking at photos I took it looks like maybe I did install RN2 with the wrong orientation. Shoot! I’m curious, do you have any advice for removing a resistor network? I’ve got fluxed and influxed braid as well as a solder sucker. But all those pins might be tough.

[Synthbuilder]

I just checked and the dot for RN2 is in the square pad. So that looks okay.

Interesting. From your description of the problem it does sound like what would happen if RN2 is around the wrong way. I wonder whether the dot has been printed incorrectly - but that would be quite a serious manufacturing error so unlikely.

I am making the assumption that when you say channel 1 you mean channel A.

If you put all channel A pots to zero and remove the power connector, measure the resistance between pins 2 and 3 of U3. It should be around 22K or lower. If it is around 68K then this would confirm that RN2 has been labelled incorrectly.

Tony

[Synthbuilder]

... do you have any advice for removing a resistor network? I’ve got fluxed and influxed braid as well as a solder sucker. But all those pins might be tough.

I would try solder sucker and braid and see if it can be removed first. But if not, wiggle it side to side until the leads break off. Then remove the individual stumps of the leads one by one. Replace with a new one.

[waldenpotato]

I just checked and the dot for RN2 is in the square pad. So that looks okay.

Interesting. From your description of the problem it does sound like what would happen if RN2 is around the wrong way. I wonder whether the dot has been printed incorrectly - but that would be quite a serious manufacturing error so unlikely.

Nope, this is_not the case. I was looking at the main board not the pot board. I haven't taken the panel off yet but I did look at a couple of photos I took while building. It looks like I DID install the network backwards on the pot board. Shoot! I always try to be so careful.

[waldenpotato]

I would try solder sucker and braid and see if it can be removed first. But if not, wiggle it side to side until the leads break off. Then remove the individual stumps of the leads one by one. Replace with a new one.

I installed the resistor networks with solder that has water-soluble flux in it. The pots and control parts are all installed using no-clean solder. I figure that I don't want to water-wash the control parts. How should I handle the cleanup when replacing the network? I figure I'll uninstall it and re-install a new one with the no-clean solder. Then I can spot clean with water around the install area.



Thanks, Tony.

[Synthbuilder]

How should I handle the cleanup when replacing the network? I figure I'll uninstall it and re-install a new one with the no-clean solder. Then I can spot clean with water around the install area.

I also use water wash solder for the main part of the build, and then use no-clean solder for the pots and other things that don't like to get wet. For rework like this repair, I would use no clean solder too. If I needed it nice and clean I would use iso-propyl alcohol (IPA) to remove any residue - usually applied on an ear bud to gently scrub it off - and then a final dab with a IPA wetted paper towel.

For surface mount component replacement I tend to use old fashioned solder with rosin or ersin flux. This is more messy than no clean, but the tiny amount of flux residue left after soldering surface mount stuff is so minimal, it is easily cleaned away with IPA.

For desoldering through hole components with a sucker and wick I will usually apply more rosin fluxed solder to the pads before attempting to remove the parts. Rosin solder just flows so much better than no clean so the solder sucker is more effective.

[Synthbuilder]

It looks like I DID install the network backwards on the pot board. Shoot! I always try to be so careful.

You're not the first to do this. I think for the next run of these boards I will make these 9 pin SIL packed resistors individual 0805 resistors. Taking that front panel off is no fun.

[waldenpotato]

My only other question:

Does replacing this part require another recalibration?

[waldenpotato]

I was able to successfully replace the resistor network. I recalibrated to make sure everything was good. It’s working! I’ll post a couple photos from the replacement process later.

[waldenpotato]

Attached are photos of the replacement. It's a little messy but it worked. I used no-clean fluxed braid and no-clean solder.

[Synthbuilder]

I used no-clean fluxed braid and no-clean solder.

You're a braver man than me. I would have used the wiggle-break-replace method. These days I have a Hakko FR-301 which does the job nicely, even on four layer boards. Somewhat expensive for occasional use but brilliant for those bigger jobs like 40 pin ICs and pots. I wish I had bought one sooner. But I have also used the ChipQuik SMD1 kit with excellent results. Contrary to its name you can use it on through hole stuff too.

[waldenpotato]

I used no-clean fluxed braid and no-clean solder.

You're a braver man than me. I would have used the wiggle-break-replace method. These days I have a Hakko FR-301 which does the job nicely, even on four layer boards. Somewhat expensive for occasional use but brilliant for those bigger jobs like 40 pin ICs and pots. I wish I had bought one sooner. But I have also used the ChipQuik SMD1 kit with excellent results. Contrary to its name you can use it on through hole stuff too.

Interesting - I've never seen these tools before. What does that ChipQuick thing do? Does it suck up the liquid solder?

[Synthbuilder]

What does that ChipQuick thing do?

That Chip Quik kit has no tools as such. It provides a flux and a special solder alloy that melts at a very low temperature. The solder stays liquid way longer than any normal solder. So you apply the flux to the solder pads for the part you want to remove. Then reflow the special solder to the pads. And then you can pull the part out of the board because the solder takes an age to solidify. You then have to remove all trace of the special solder from the part (if you want to reuse it) and the board. The best way to this is to wick or suck it up, and then apply normal solder, and then wick or suck that up.

It's horribly expensive but you don't need to use much at all.

Here's Dave showing how to use it:

[Leverkusen]

This looks quite interesting! I honestly tried and practised but never got along with solder wick or those hand suckers. It was always just getting a real mess.
Things improved massively when I got myself a cheap desoldering station. It has to be handled carefully to not get constipated and it's terrible to disassemble and clean it then but for occasional use it was really worth the price.