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MOTU 828 mkII USB crackle
Old 5th July 2010
  #31
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Hi, I have the same problem with the crackling, first on mic 1 now on both. I was thinking, isn't there a way to transform these mic/inst ins into line ins? I don't have any use for the pre's, but would love the extra line inputs for 10 track recording.
Thanks guys!
Old 5th July 2010
  #32
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LeeYoo's Avatar
 

Hi polchilipepper.

AD/DA converters were all Asahi Kasei AK4528 in the unit I looked at. Same on the mic channels as on the line channels.
Full data available on the web from this manufacturer, including pre/input examples.

You could try if the mic inputs accept line level without clipping on the lowest gain setting.
You could then replace the pots with fixed resistors. Otherwise you have to copy the line-in circuitry. Maybe difficult without a manual.
Old 2nd August 2010
  #33
Gear Nut
 

Spares

I have diagnosed the problem to be a dodgy gain pot, as LeeYoo described. However i contacted the UK distributor to try and get and replacement daughter board. They put me in touch with their authorised repair people, who said they couldn't send me as spare as they don't have them, and it would cost me £100 to send them the whole unit to fix the problem. The guy was saying they don't have spares as they repair everything down to component level. (Sounds like BS)

Did anyone else have any luck getting hold of any spares to fix this problem.

Cheers

Phil
Old 3rd August 2010
  #34
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LeeYoo's Avatar
 

Hi Phil,
Good to hear that you have confirmed my findings.
You said, they repair everything to component level.......
There are TWO components on that little board: The two gain potentiometers. Nothing else!!
Maybe US$2.00 each. Plus $200.00 P+P??
Easy to replace yourself, if you can get them.
Somebody in China must have a box full of them.
Leo..
Old 6th September 2010
  #35
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Any way to find the component ?

Hi LeeYoo,

I have the same problem with my motu, and with my step-brother we decided to replace all the capacitor.( he thought it was the cause).
But the problem is still there. A gui from a french forum on the motu give me the link of this post (because there are a lot of people with the same problem)
If I understand what you said (my english is not very good), the problem comes form the potentiometer.
You create something to be shure of that but it freezes the gain. So it's not a solution for me.
you said :
"Replacing is the only option. The problem is that the pots are special ones. one track is 20k, the other one is 2k AND they are reverse log (type C). Anybody out there that can supply them?"
is there a way to buy new ones, is the card is too old for finding them?
Regards,




Saisissez du texte, l'adresse d'un site Web ou importez un document à traduire.
Annuler
Old 7th September 2010
  #36
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LeeYoo's Avatar
 

Bonjour ZORAX.
My French is not very good, so I will continue in English. Yes, you have understood it right. The gain potentiometer seems to be the problem, and I don't know if MOTU will supply them to you.
I have supplied several people with a fixed-2-resistor plug to replace the potentiometer(s).
Sure, it freezes the gain, but this way you can make sure it is the potentiometer.
No soldering needed, just plugging it in.
And no, the unit is not too old for fixing. These potentiometers are still used today in new gear.
Let me know if you have problems with replacing the pots with fixed resistors. I could post you a set (no charge).
Just send me a private message with you address/P.O. box.
Regards,
Leo..
Old 21st October 2010
  #37
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Hi,
I just remove the PCB with the two potentiometers. I place a cable between the pin 1 and 3.
I try like this.
The gain is very high, but there is no more crackle !!
So I try to find a seller to get the pot, but no one in France can provide them.
Could you please tell me if a website anywhere can provide them.
Best Regards,

I wonder why Motu use such a pot. Is it important having both resistance? What is the aim of the second one ?It seems to be for high level signal...
Old 16th December 2010
  #38
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Replacing backlite LED

Remove the front panel from the unit. Don't forget the little srews next to the mic sockets and a nasty hook on the circuit board that locks the two boards together. Unplug the two plugs from the MAIN BOARD, not from the front. This plug has got less pins than holes, so you could make a mistake here, plugging it in again (like I did). Work on a clean surface, to prevent dust building up behind the perspex front. Remove the display (note that one screw has a plastic washer). Remove the solder on the two contacts, next to the display with a solder sucker, or with solder litze. Break away the very small strip with the smd led on it, by pulling on the desoldered wires. This is glued onto the side of a perspex sheet, that runs under the display. Buy a 3mm HIGH BRIGHTNESS green LED from your local electronics store. The green means the light, not the colour of the plastic. It should set you back close to US$5.00 , don't use a normal one. Cut off the shortest leg to 10-12mm (half an inch) and bend it 90 degrees. Tack this short leg to the bottom contact, making shure, the front of the led shines into the middle hole (indent) of the perspex plate under the display. You can see this by lifting the tin foil a bit. If it fits, cut off the other leg and solder it to the top contact. Stick a piece of black tape over the led to prevent the light bleeding into the neighbouring display. Assemble in reverse order.
Post your findings..

Dear Leeyoo,

Many thanks for your clear explanation regarding the replacement of the backlite LED of the MOTU 828 MKII.
Based on your description, I was been able to replace the defective backlite LED.
I've made a picture document of the repair actions, which I like to share on the forum. (Repair defective backlite Motu 828 MKII 02.doc)

I've tried to upload it, but am not sure I succeeded.

Best,

Erik
Attached Files
Old 21st December 2010
  #39
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LeeYoo's Avatar
 

Hi Erik,
Impressed with your document. I was able to remove the front without removing the main board from the bottom shell, but it seems easier this way.
I think you also used a 5mm LED instead of a 3mm one. No problem, but a 3mm LED is smaller, and easier to install.
You can also clearly see the mic. gain pots on these pictures. The daughter board with the blue controls. This is the other BIG problem with this unit.
This can be removed just by lifting it up after removing it's screws. No need to dismantle the whole unit. I will try to upload some close-ups of this daughterboard soon.
Thanks Erik.
Leo..
Old 28th December 2010
  #40
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motu trim pots just went bad!

I contacted Motu and got the same deal, $100 to fix it plus shipping. I would rather put that money toward a new unit.

LeeYoo, do you still have the replacement parts? could I purchase them from you?
Old 29th December 2010
  #41
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LeeYoo's Avatar
 

Hi all,
Here some pictures of the gain board.
Leo..
Attached Files
File Type: doc Microphone gain daughter board.doc (224.5 KB, 1737 views)
Old 29th December 2010
  #42
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LeeYoo's Avatar
 

I saw in another thread that some people also had problems with mechanical buzzing noise inside the unit. This was also a problem in our unit.
This is how I fixed it. Sorry Erik, stole part of your picture for that.
Leo..
Attached Files
Old 30th January 2011
  #43
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No problem LeeYoo,
Your posts made me able do repair my 828 myself! Thanks for that!
And even, anyone is free to use the pictures in the document or even the complete document, .... as long as one don't claim it's his own document! tutt
Old 23rd February 2011
  #44
Here for the gear
 

I just simply rerouted the v-ref voltage further up the signal chain so that it's not going through the dirty pot. This eliminates the v-ref voltage from sporadically changing due to the weakened stability of the pot. Motu is the ONLY interface company who i've seen who routes the v-ref through a pot. That is just stupid.

you don't need to replace the pots. just take out the resistors that feed the v-ref to the 2134's and put new isolating 10k (at least 10k) resistors on the other side of the 47k resistor network or solder them straight to the input pins of the next buffer stage. but then you take some ultra fine hook up wire and hook up the v-ref voltage to those resistors.
Old 23rd February 2011
  #45
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LeeYoo's Avatar
 

Hi Daniel,
Thank you for your reply.
I thought there would be a way to get the DC voltage of that pot, but I did not try, because I did not have a schematic diagram.
Do you have a diagram, or at least the part involved, and could you please share it.
Or make a simple drawing, so we can make it into a "how to fix" document.
Please PM me if you feel like you might be stepping on MOTU's toes.

This is the A/D D/A chip info. Page 25 explains the analogue input.
http://www.asahi-kasei.co.jp/akm/en/...k4528_f01e.pdf

Leo..
Old 11th March 2011
  #46
My MOTU 828 MK2 IS REPAIRED SUCCESSFULLY!!!

Daniel at Black Lion Audio performed my repair.

Again, he figured out that the v-ref voltage needed to be re-routed further up the signal chain so that it's not going through the dirty pots, it eliminates the voltage from sporadically changing due to the weakened stability of the pot.

His repair was cheaper than MOTU's $100 + shipping scam. *They should design something correctly to begin with!!!

Thanks Daniel (if you ever even read this) for taking care of my 828 for me.

Brad | YRLK
Old 14th July 2011
  #47
Gear Nut
 
Zencatt's Avatar
 

Great information all, thanks very much for sharing. LeeYoo, I just bought an 828 MKII and it has a fairly loud, consistent buzzing that is causing me to send the unit back (otherwise okay, I haven't heard any crackling lately).

Just wondering how that glue fix works; is it gluing the transformer "bobbin" to the rest of the assembly to stop the vibrations? How much did it reduce the noise? I'm afraid that this unit would have noise showing up in most tracks. How much would a tech (or Black Lion) charge to do this. Thanks very much.
Old 14th July 2011
  #48
Lives for gear
That is a scam that Motu is running with that $100 repair/replacement program. It's like a car company trying to charge you for a recall. All of those units have problems and they know it. But it's consumer gear so they don't care. Or they're hoping to ride it out.
Old 20th September 2011
  #49
Gear Nut
Starbearer, I'm also interested in what leo was asking.

Would you be able to provide greater detail on how you rerouted the vref?

Many thanks.
Old 20th September 2011
  #50
My 828mkII also has a 'ticking' noise on the mic pres. But they sucked from the word go, even before the geiger-counter like ticking, so I shined that on.


HOWEVER... from time to time it has also developed the far more serious problem of blasts of noise across all channels. At one point this was happening once or twice a day and interfering with recordings and other audio work.

I finally found instructions on doing a reset of the device -- and that seems to fix the problem for long periods. (In fact, it's probably been over a year; I've had this since 2004.)

Here's how to reset the 828mkII:

MOTU.com - I get high-pitched noise coming out of my 828mkII, how do I factory reset my interface?
Quote:
Follow these steps to restore the 828mkII to Factory Default Settings.

Disconnect the firewire cable from the 828mkII
Press the Setup knob
Turn the Setup knob all the way to the right
Press the Select knob
Press the Value knob
Power off the interface and plug the firewire cable back in
Power the interface back on.
The same steps can be followed to restore the Factory Default Settings on a Traveler.
Keep in mind -- this does nothing for the mic pre crackling/ticking noise issue.
Old 4th January 2012
  #51
Here for the gear
 

Quote:
Originally Posted by theblue1 View Post
My 828mkII also has a 'ticking' noise on the mic pres. But they sucked from the word go, even before the geiger-counter like ticking, so I shined that on.


HOWEVER... from time to time it has also developed the far more serious problem of blasts of noise across all channels. At one point this was happening once or twice a day and interfering with recordings and other audio work.

I finally found instructions on doing a reset of the device -- and that seems to fix the problem for long periods. (In fact, it's probably been over a year; I've had this since 2004.)

Here's how to reset the 828mkII:

MOTU.com - I get high-pitched noise coming out of my 828mkII, how do I factory reset my interface?


Keep in mind -- this does nothing for the mic pre crackling/ticking noise issue.
I did this and it seemed to make mine worse. I have the shi**y MOTU/Windows driver issue, not the mic pre crackle/fizz. this is unfortunate because I have a lot of work to do on this thing and near zero dollars for a replacement interface. I've had this for a little under a year and haven't been able to get it to play nice with my pc since day one. The upside is that it rarely (next to never) does it while I'm mixing in the DAW. Mostly when I'm trying to play something back in itunes/quicktime/vlc, etc. The potential downside is that once I start running a bunch of mics through it and hit record that it will melt down and leave me feeling powerfully embarrassed. I hate this thing.
Old 30th January 2012
  #52
Here for the gear
 

Same crackles issue on preamp here in France...

Quote:
Originally Posted by starbearer View Post
I just simply rerouted the v-ref voltage further up the signal chain so that it's not going through the dirty pot. This eliminates the v-ref voltage from sporadically changing due to the weakened stability of the pot. Motu is the ONLY interface company who i've seen who routes the v-ref through a pot. That is just stupid.

you don't need to replace the pots. just take out the resistors that feed the v-ref to the 2134's and put new isolating 10k (at least 10k) resistors on the other side of the 47k resistor network or solder them straight to the input pins of the next buffer stage. but then you take some ultra fine hook up wire and hook up the v-ref voltage to those resistors.
So, more details on Starbearer's solution would be very appreciated here ! A little sketch maybe ?

Thanks in advance !
Old 30th January 2012
  #53
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Ain't Nobody's Avatar
 

Can't say I have a solution, but crappy pots all around for my MK1.

One of many things I just plain did not like about that interface.

Crackled very badly... worse than any other piece of gear I've ever had.
Old 7th February 2012
  #54
Here for the gear
 

to anyone experiencing crackling preamps on their MOTU 828 mkii....

remove the daughter board with the gain pots on it and simply reheat the solder joints. this worked for me. hopefully you only have a cold solder joint as well.

cheers,
BD
Old 7th February 2012
  #55
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LeeYoo's Avatar
 

Hi band_master. Welcome to GS.

We did that...in post#10
If you read all the posts, you will find that this is only a temporary fix.
The crackle will come back, because the real problem lies inside the pots.
Leo..
Old 7th February 2012
  #56
Gear Head
 
sonick909's Avatar
 

I've had problems like this with ham radios..... problems are often traced back to tin whiskers from politically correct solder lacking adequate lead
Old 7th February 2012
  #57
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LeeYoo's Avatar
 

This crackle problem has been traced to DC voltage on the pot.
The carbon tracks of this very small pot (too small) are two circles, an outer and an inner one, very close together on one wafer.
I think this is the problem:
Moisture and DC between the tracks migrates the metal, and over time it causes a (high resistance) short between the two tracks.
I did actually measure that high leak resistance between the 2k and the 20k track with a DMM.
This leak is not constant, and this is the crackle.
The proper fix is to change the circuitry, to get the DC voltage off that pot.
Starbearer knows how, but he won't tell. I don't blame him, because he works for Black Lion.
Understandable for the clients in the US, but a problem for the rest of the world.
High time that a MOTO tech posted a detailed fix here.
Leo..
Old 21st February 2012
  #58
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NebulaZero's Avatar
 

Quote:
Originally Posted by LeeYoo View Post
I saw in another thread that some people also had problems with mechanical buzzing noise inside the unit. This was also a problem in our unit.
This is how I fixed it. Sorry Erik, stole part of your picture for that.
Leo..
Yellow star? Am i missing something? Where do i put the epoxy?
Old 21st February 2012
  #59
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LeeYoo's Avatar
 

Hi NebulaZero.
The link in post#42 shows you where to put the glue.
The spots, marked with 4 yellow stars.
No point in putting a lot of epoxy all over the transformer.
Leo..
Old 21st February 2012
  #60
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NebulaZero's Avatar
 

ahh ok thanks i see it now i was opening the word doc with my iphone and the yellow stars wernt showing, but in my i see them now on my computer!
thanks LeeYoo!
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