V-pot not operating correctly

[studiodaz]

Hello, its been some time since I have used my D8B as I was having problems with it not always switching on and all the LED would pulse on and off. Anyway with lots of time on my hand after being furloughed from work I thought it would be a good opportunity to learn how to solder the SMD, ceramic, caps 0.1µF, 50V model 0805 and fix the Rail Capacitor problem on the main brain board. After doing this my D8B is back a live again but I have one problem I can't seem to work out a fix for.

Every V-pots even the control room volume will not work correctly. The pan encoder V-pots for example seem to be stuck at 12 o'clock but if I keep spinning them to the right round and round the LED ring jerks very slowly and moves to the right pan but spinning the V-pot to the left it very slowly struggles to move the LED ring to 10 o'clock even after many many times spinning the V-pot. The control room V-pot is stuck and will not move at all. When using the mouse the LED rings work fine and also using HUI mode shows the LED rings moving when making changes on my DAW.

I am guessing there is a communication send problem with the V-pots but I am not sure where the fault could be coming from. When changing the SMD, ceramic, caps I only changed the one that were highlighted in the picture. Could any of these be causing this problem or is it some other area I need to look at?

[Y-my-R]

Hi studiodaz,

It's possible that it's an electrical/electronic problem, however, of the 3 D8Bs I restored that had all been sitting for an extended period of time, they all just needed some electronics cleaner in the V-Pots.

I used Deoxit Fader F5 for this. The grey caps pull right off. I'd just spray as little as I can in there, move the knob around a bunch of times, spray another minimal amount and repeat. Then move to the next V-Pot.

So far, this has restored all the V-Pots on the 3 units, and they all work fine. They feel a little looser, but work without problems.

I'm glad I never had to deal with the rail-cap problem, though. Respect that you were able to solve this! I think if I'd get hit by that, I'd finally give up on my D8Bs

Best of luck!

[studiodaz]

Hi studiodaz,

It's possible that it's an electrical/electronic problem, however, of the 3 D8Bs I restored that had all been sitting for an extended period of time, they all just needed some electronics cleaner in the V-Pots.

I used Deoxit Fader F5 for this. The grey caps pull right off. I'd just spray as little as I can in there, move the knob around a bunch of times, spray another minimal amount and repeat. Then move to the next V-Pot.

So far, this has restored all the V-Pots on the 3 units, and they all work fine. They feel a little looser, but work without problems.

I'm glad I never had to deal with the rail-cap problem, though. Respect that you were able to solve this! I think if I'd get hit by that, I'd finally give up on my D8Bs

Best of luck!

Thanks for the tip. It would be great if the pots just need cleaning but it's very strange that they are all not working ☹️.

The caps were easier than I thought they were going to be to replace but I was using a magnifying headset with light on it so I could see them properly.

[Jondav1120]

Hi, Studiodaz, I can echo Y-my-R's experience. All the V-pots on a board that I got very cheaply off ebay were doing pretty much what you describe (some worse than others). All were sorted by an application of Deoxit and some heavy exercise...

Hope yours respond in the same way!

Regards

John

[studiodaz]

Today I tried cleaning the vpots but no change unfortunately, next I took out the brain board again to have another look and found that one of the cap's solder had ran into a track that connected it to one of the resistors. I resolder the cap and now all the V-pots above the faders are operating normally again.

Unfortunately that didn't fix the control room volume pot or any of the other V-pots on the right hand side/ output side of the desk.

[studiodaz]

V pots now working. I had to replace IC U8. I couldn't get the exact replacement but this one did work ok. RC4580IDR. https://uk.farnell.com/texas-instrument ... 7-00001003

[H4RR1S]

uh, i got a very similar problem and I tried a lot of this post: viewtopic.php?f=7&t=1279&start=40#p17269
all my voltages are normal.
Did your faders move on startup? Mine don't...

[studiodaz]

My first problem which I still have not fixed was that not all of my layer select button work and when I press solo on fader 24 it selects one of the layers and solos that fader on that layer instead of the input layer. I put up with this for quite sometime by not soloing on fader 24 and by selecting the layers using the F keys on the keyboard. Then at some point the desk stopped booting up and pulsed the LEDs and faders. So everything I have posted above fixed the desk to get it booting and then fix V-pots. I just need to find away to fix the channel select buttons or whatever is stopping them from sending the command to change layer. If I can fix that I will then replace 3 sticking faders.