[BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread

Potato Cakes said:

Polarity of LEDs soldered backwards?

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That was my first thought. The polarity is correct as per the instructions as well as by way of confirming this with other vp28s I have with working LEDs. Thanks for the response!

Allecstatic said:

I just realized the light indicators on the 4 vertically aligned push buttons are not working even though the buttons themselves are. I resoldered to be sure and visually inspected the area - still not working. Anyone run into this problem or know what the issue may be?

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My first thought was the same as Paul's, polarity of the LED's. The other thing I have seen is leads too long that hang off the back edge of the pad and short to ground. They are in a string so if one down stream is wrong then none will work. You can probe at the pads to make sure you have appx 16VDC starting with the anode pad/lead of the 48V LED and working towards the top of the module.

jsteiger said:

My first thought was the same as Paul's, polarity of the LED's. The other thing I have seen is leads too long that hang off the back edge of the pad and short to ground. They are in a string so if one down stream is wrong then none will work. You can probe at the pads to make sure you have appx 16VDC starting with the anode pad/lead of the 48V LED and working towards the top of the module.

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Thanks Jeff. I'll check that out. Is it possible that the LEDs can become defective if the leads end up shorting to the ground or if the polarity is swapped?

Allecstatic said:

Thanks Jeff. I'll check that out. Is it possible that the LEDs can become defective if the leads end up shorting to the ground or if the polarity is swapped?

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No.

OK,

I'm still trying to get my last two VP28's sorted out. I never got a response to my last few queries, so I decided to just try to reflow all the solder (or most of it) on one of my VP28's. I think I solved whatever problem I was having. And so now I have new problems, of course.

Before I was getting a squeal after certain volume was reached. Now, no squeal.

Before the VP28 was VERY loud, louder than the other six that are working properly.  This time, when I turned it on it was very loud, then it made a "pop" and it became closer to what I expect it should be.

Now, it makes a light crackling noise that's easier to hear at high volume and it also has a hiss that is audible even at low volume, but gets louder as you increase the volume. It IS passing signal.

Other details that may or may not be useful for diagnosing the current situation with this VP28:

I did not reflow all the solder. I figured I should rule some things out and skip them. I did NOT reflow solder to any of the switches, and in the case of the gain and output switches, I did not reflow any of the solder to any of the resistors in line with those switches. I also did not reflow the solder to the chip that controls the LED's, and I did not reflow any of the pins for the Op Amps. I did nothing with anything associated with the HPF.

Then, and this might be my hiss, I cleaned the board with alcohol and a plastic brush. I figured it was messier than usual after being reflowed, and it WAS messier than before. However, the board is now a sticky mess, even after being scrubbed several times. When I first plugged it in, it got no power. Then I unplugged it and cleaned the gold fingers with more alcohol and q tips and plugged it back in and it got power and worked, but just had these noises.

As always, thank you Jeff and everyone else. I have a little time this week to pay attention to these things. I'm hoping I can get them figured out this time.

Did you compare voltages to your working VP28's? Seems like that would be the next step after checking soldering and component placement. And if your soldering now is messier than before you may have some new sweet bridging action.

Thanks!

Paul

Commander Fluffypants said:

Hi folks,

I have six VP28's, five of which work very well. The other one has some strange symptoms. I believe this is the one I posted about a while back. (Due to life situations and an historically hellish winter here, I've hardly done any recording at my studio, and no full band stuff where I'd need all my inputs, until now when I'm noticing this issue.)

First thing I did was swap out my DOA's with ones from a working unit, so I know it's not theDOA's. Too bad. That would be an easy fix. The symptoms are a HUGE pop when engaging the pad, a huge pop when engaging the phantom and a bit of a pop when engaging the mic/line switch. Phase button makes no pop. If that was it, I could live with it, but none of my other units make these noises and more important, there is a bit of hiss and hum in this one and possibly some signal distortion. It's not that loud, but it is audible, especially at high gain. Both knobs affect the volume of the noise(s). None of my other VP28's make these noises. As far as I can tell, everything is in correctly.

Any ideas?

Thanks, as always!

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So today, I went one step further and carefully cleaned the entire main board of this one last VP28 that's not working properly. Because it's sometimes hard to get a response, I'm rereading this thread again and searching this thread to see if anyone has had any similar issues. What I found is that the condition of this preamp hasn't changed in years! This thing is behaving exactly as it did when I described it  years ago... Even with the reflowing and cleaning.

Can anyone help me with this problem?

I did notice that someone else who was using a Radial Workhorse was having a similar issue, although not exactly the same.

I notice some strange behaviors that *might* point to the Workhorse, but I'm not sure. The loud pop that happens on this preamp when engaging phantom power shows up on other channels! But it's not that simple. I did some experimenting.

First, any and all linking buttons on the Workhorse are OFF.

There are no microphones plugged into anything.

I opened up Pro Tools and had a track set up for every channel of the workhorse (8 VP28's! 7 that seem to be working great.) I started with the preamp in question in the third slot of the Workhorse. When I hit the phantom button, there was a loud pop showing up in my DAW for that channel. A lesser, but still loud pop showed up in the forth slot. And a lesser pop showed up on the second slot. A similar pop happens wit the pad button and it also shows up to a lesser degree on the adjoining channels.

So I swapped slots two and three. The preamp behaves exactly the same and the neighboring channels behave the same as well. It does not matter what slot the preamp is in. I *think* this rules out the Workhorse.

One other symptom, however, might just help nail this issue:

No matter what slot the preamp is in, when I engage phantom on any of the other preamps, THIS ONE pops, not the ones that had phantom toggled. That's gotta be some kind of giveaway.

Thanks again, and someone please help me. I've actually been trying to make this one last preamp work for years!!!

Potato Cakes said:

Did you compare voltages to your working VP28's? Seems like that would be the next step after checking soldering and component placement. And if your soldering now is messier than before you may have some new sweet bridging action.

Thanks!

Paul

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Thanks Paul!!

You got your post in just before my last post. My soldering is pretty good on this. I'm hoping the last issue I listed in my post above is some kind of hint as to where the problem lies.

I wouldn't know where to begin comparing voltages. If it comes to that, is that something I do in the jig with the power on? I know there's a PDF somewhere of test points. Is that what you're talking about?

This is Rev A.2, BTW.

Do you have an extension test jig for 500 series units? It is necessary to have when building modules.

As for voltages, you would start with making sure proper power is getting to the DOAs. Then you can use this as a guide:

http://www.capi-gear.com/catalog/images/gallery/VP28/Build-docs/RevB/CAPI-VP28-Rev-B-Test-Points.pdf

It's for Rev B so you would have to email Jeff and ask which components  those test points connect to and just apply that to your Rev A. It should be close to the values listed in the test point guide.

Thanks!

Paul

Potato Cakes said:

Do you have an extension test jig for 500 series units? It is necessary to have when building modules.

As for voltages, you would start with making sure proper power is getting to the DOAs. Then you can use this as a guide:

http://www.capi-gear.com/catalog/images/gallery/VP28/Build-docs/RevB/CAPI-VP28-Rev-B-Test-Points.pdf

It's for Rev B so you would have to email Jeff and ask which components  those test points connect to and just apply that to your Rev A. It should be close to the values listed in the test point guide.

Thanks!

Paul

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Thank you again, Paul.

I do have the jig.  Does the fact that this preamp pops when any other preamp in the Workhorse has it's phantom power switch toggled narrow anything down? And it happens no matter which slot this preamp is in.

I'm still digging around this thread. I found the Test Points PDF for Rev A.2. If it needs testing, I'm going to have to ask some silly questions first:

Which probe goes where on my DMM for this test? Now which one goes to ground on the VP28. And where is ground on a REV A.2?


I need instructions that a drummer can understand...

Thanks again...

Com (-) to ground. + to test points. Look up API 500 series edge connector pinout for reference.

I appreciate the response, but it's not down to drummer level...

First of all, I have no idea how I'm supposed to have something in the jig and probe the card edge at the same time.

I need to be told physically where to put the probes. The RevA.2 PDF tells me where to put one of the probes, but I'm not sure which one. The other probe goes to ground. Great. Where is ground? On the card edge that's in the jig? The one labelled "audio ground" or the one labelled "PSU Ground"? Makes no sense. There's got to be ground somewhere on the board or maybe somewhere else altogether.

But also, I'm really, REALLY curious to know if the one particular symptom where phantom power toggling on OTHER pres causes THIS pre to pop tells us anything at all about the nature of the problem.

Bumping.

Need to know a few things:

Where do I put my probe for ground on the RevA.2 board? And do I do these tests with the DOA's in or out?

When I toggle phantom on any VP28 in my rack, this one, and this one only, makes a loud pop. Clipping. It does this no matter which slot it is in. It als pops when I toggle it's phantom and it's pad switch also makes a huge pop. Does this help narrow down the problem I'm having with this VP28?

jsteiger said:

No.

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Although the leads from the LEDs were not touching the board, one of the connections had a bit too much solder which I believe WAS touching the board. That solved the issue. Just wanted to post in case someone runs into this issue down the road. Thanks again for the help, Jeff!

Hi there,

Still looking to understand a few things so I can finish this last VP28; the only one of eight that has had any serious issues. It has been languishing in a box for years. I haven't been able to get a complete response here for years.

I want to know if the fact that this pre not only pops really loud when engaging phantom and pad and also pops really loud when phantom is engaged on any other pre tells us what the issue might be.

Next, if I'm going to test this pre, I need to know how. Am I to test it under power? With DOA's in or out? I found the test points PDF for Rev A.2, but I actually need to know which probe goes to the test point and which one goes to ground, and I need to know where ground is.

I've had this VP28 in near working condition for years now. When I have time, I start a conversation here to make progress on it and get a few responses, but never get all the information I need to take any steps to solve its issues. Then, after getting no response, life and work get in the way and months later, I start the process all over again.

I'm bumping this thread hoping that someone will understand what information I need in order to make some progress on this.

Thank you.

help...

Commander Fluffypants said:

help...

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Remove the pre from the rack and measure DCR between gold fingers 8 and 10. Do this in mic mode with all other pushbutton switches out. Next do the same with the phantom switch engaged.

jsteiger said:

Remove the pre from the rack and measure DCR between gold fingers 8 and 10. Do this in mic mode with all other pushbutton switches out. Next do the same with the phantom switch engaged.

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Thank you!!!

I actually did this and posted the results a while back, and I did it in mic mode as you instructed, but I don't believe I A/B'd with the phantom button in.

The results with the phantom NOT engaged are:

Commander Fluffypants said:

This is what I have (almost.)  3.61k for 5 to 8 and 5 to 10 and 27.5 for 8 to 10.

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I will be at the studio tonight and I will double check all of this and post the results. Please don't forget about me. Check back soon. I understand that it can be frustrating  guiding a neophyte through this process and I appreciate the help. I also really, REALLY appreciate that you're instructing me to specifically remove the unit from the rack as well as other instructions that may not be necessary for people who have a better grasp on electronics.

And the results are:

27.6 no phantom

27.5 with phantom