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MOTU 828 mkII USB crackle
Old 24th June 2013
  #91
Gear Nut
Hi Leeyoo.
I didn't mean to sound like I was challenging you. I know little about this kind of thing.
I just thought I'd mention that I did something different from your cleanup.

I was pretty vigorous with my cleaning. Electrical contact cleaner and a qtip.
I just scrubbed and scrubbed until black stuff stopped coming off.

Probably not the best tactic in the world but it was broke already, right?

I'll make sure I post back if/when the pot goes wrong again.

Cheers.
Old 24th June 2013
  #92
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I admire people who think "outside the box".
They are the ones who dream up the solutions.
Keep us posted.
Old 26th June 2013
  #93
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Quote:
Originally Posted by LeeYoo View Post
This if for all of you slutz who want to try the fix for themselves.

Get a "header terminal strip" from your local electronics part store.
Jaycar Electronics - Search results HM3212
And some small resistors:
2x 180ohm and 2x1k8 for 75% gain and/or
2x 330ohm and 2x3k3 for 50% gain.
Note the 1:10 ratio. You can use any value from 0/0ohm to 2/20kohm.
Snap two sets of 4 pins from the strip.
Solder a 180ohm between pin 1 and 3 and a 1k8 between pin 2 and 4.
Solder them on the shortest pins and make another one.
Use the 330/3k3 set if you want 50% gain.
Unplug the power of the Motu and remove the top (3 screws).
Locate the pot board behind the mic sockets and remove the two screws that hold it in place. Lift it up to unplug it from its socket. Remove the knobs and wrigle it out of the front.
Plug in the thinghy's you made, making shure, the lowest value resistor (180ohm) is pointing to the closest corner. Make sure, the resistors are not touching each other. Close the unit and put the old parts in a ziplock. You might need them again.
Try the unit with the mic input software cranked up again.
Post your findings..
Hello there from a new Poster: I performed this mod to 2 828 MK II Firewire units, worked out great! I was in a hurry, so I just bent/formed the resistor leads and inserted them into the open socket positions on the 828 circuit board when the pot daughter board was removed. I know that using the headers is the best way, but if there is a rush (read: Session) this method will work. BTW, the problem with my units was not crackling, but intermittent/rough taper of the gain pots. I am happier with the set gain values (75%), rather than the gain jumping all over the place as was the original fault with my interfaces. Hope this helps. Thanks again, LeeYoo!
Old 31st July 2013
  #94
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Thanks for this thread, I've been going crazy trying to trace this.
Old 12th September 2013
  #95
Gear Head
 

Found similar looking pots made by Vimex (SIS14 Series-index). I have seen Bourns dual pots with separated cups (http://www.bourns.com/data/global/pdfs/97_99.pdf), maybe having separated cups can fix the problem in the long term?
Old 12th September 2013
  #96
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Hi mecano.
Standard 14mm lin/log pots are easy to find.
Reverse log is a bit harder.
Reverse log with two different values seems to be impossible.
Leo..
Old 14th September 2013
  #97
Gear Head
 

Hello Leo,
if you read the Bourns pdf you'll see that C taper (reverse log) is available.
Old 15th September 2013
  #98
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Two different values in one 14mm pot.
2k/20k reverse log.
For the price of a normal pot.
That would help a lot of people...
Please provide a link...
Old 16th September 2013
  #99
Gear Head
 

I just phoned Bourns (Switzerland) but no technician was available. I just got one of their distributor technician on the phone, we had a very nice talk. He'll be able to provide (if existing) solutions from Bourns, Vishay and BI, 97-99 models from Bourns came in the conversation. As I'm looking for pots for a 896HD, please provide an exhaustive description of the 828 pots (I guess they are just the same) to be sure. I'll then go back to him.
Old 16th September 2013
  #100
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It looks like the pots in the 828 are made by ALPS.
Two different reverse log values on one wafer. C20k/C2k
ALPS documentation clearly states "not applicable to DC" for these models, and DC seems to be the problem in this MOTU 828 design!!
IMHO, the best way out is to design a whole new daughterboard that would hold two "normal" 2-section pots.
Then everyone could just replace the daughterboard in 5 minutes, without soldering/modding the main board.
Almost any (modular) 20k/2k reverse log (C) pot can be used.
Bourns seems to be 5x the price of ALPS according to my info.
There is not a lot of clearance between the daughterboard and the top cover, so a 14mm type is the max you could fit.
The shafts might have to be extended. I did not find any modular pot with long shafts.
Can't measure things, since I don't have a unit here.
Leo..
Attached Thumbnails
MOTU 828 mkII USB crackle-motu-pots.jpg  
Old 7th October 2013
  #101
Gear Head
 

Hello Leo, fixed my problem, bad solders and behaving switch on the rear, so I've given up on the search. Indeed the best way for a 828 would be to replace the daughter board but i'll be even more picky to find I guess :/
Old 27th November 2013
  #102
bch
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Hi! new forum member here.
First, thanks LeeYoo for posting a solution to the crackle problem. I have this on one of my MK2 preamps. Really anoying

I've been looking for a pot to replace the faulty one but I havent find that yet, and it seems very unlikely to get the very same. Did you find a suitable part to make the replacement?

I guess the best shot is to make a new daughter board. I think I could do it myself (first a prototype, then maybe a printed one).
Could you be so kind to point me out to a suitable pot I could use?

Thanks!
Old 25th December 2013
  #103
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LeeYoo, your info here and elsewhere on the 828 backlight fix has been invaluable to me. Let me add a couple of details from my experience:

I thought I'd try replacing the (dead) green LED on my 828 mkII with a red LED. Picked up a 3 mm red LED from a local electronics shop and soldered it into the two holes marked 'A' and 'K' - the anode and the cathode for the LED. These are connected to the big solder blobs that the original backlight LED is connected to. The 3mm LED is a great fit - easy to position it so that it is pointing right into the slot where the original SMD LED was:




Put the 828 back together fired it up and.... nothing. Took it apart and tested the LED and it was dead. Measured the voltage going to the LED - it's 11.5V! (LeeYoo mentions this is a rail voltage on another forum). Vf of my red LED is about 1.8V whereas Vf of a green LED is somewhere around 3V, so perhaps the current limiting resistor on the main board is just enough for a green LED but not enough for a red LED. With a superbright green LED connected, I measured a Vf of 3.6V and a LED current of 42 mA! No wonder these LEDs are getting fried. The current limiting resistor on the main board is on the bottom side, as far as I can tell. I got the LCD/knob board out without removing the main board and wanted to leave it as is so I added a 330 ohm resistor in series with the anode. This gave a current of 17 mA for the red LED, 3 mA shy of its 20 mA rating. The resistor replaces the anode terminal to which one of the stray ribbon conductors connects. A little blob of solder on the resistor's terminal makes it thick enough to get a firm fit with the connector:



The result:

Old 26th December 2013
  #104
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Hello from Germany, i am new here but long in record business.
i´m using the 828mk2 and my traveler (both firewire) for a long long time with my old laptop acer PC and Thinkpad. Only my 828 starts has some problems with mic-cracle, software/driver cracle (all output leds are blinking in random) and no backlight at all.
I will thank you all for your postings and helps because i could repair all of this by myself.
The backlight-repair.doc in post#38 is wonderful; my backlight is on (blue-white)
The cracle in both MicroIns are gone with 100 Ohm - 1kOhm Resistors; yeah (Originally Posted by LeeYoo),

The cracle (when all output leds are on) ,software-cracle?, is gone when i simply set in the Motu Console for my 828 - to Optical In: TOS Link, but no optical cable is in. (thats my workaround)

hope I can help with my stupid english.
Old 7th March 2014
  #105
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Hi, new member too.
My 8282 mkII is the firewire one, having the same crackling problems for years, first on input 1 and later on input 2, first on some positions and later on the whole range.
Right now, I'm back into recording in my home studio and thanks to LeeYoo I have my 828 almost in shape.
I did the pin thing 100ohm/1000ohm for input 1 and for input 2 I wired pins 1-3 and 2-4.
My doubts are:
-Wiring pins 1-3 and 2-4 makes a full gain increase? (Because if you wire pins 1-3, then pins 2-4 should be wired too)
-Pins are numbered looking at the 828 starting on the left, right?
I use both inputs for microphones, so the 330ohm/3k3ohm or any other low gain combination is not suitable for me.
Now my 828 sounds clear.
Old 7th March 2014
  #106
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Good to see that so many members have been able to fix their mic input and display.

italio, I just named the pins 1,2,3,4 for easy reference.
Pin 1 starting from the corner of the unit.
You have to connect pin 1 with 3
And connect pin 2 with 4

If you just use wires, the gain is maximum.
If you use resistors, the gain is less.
Higher values is less gain,

Resistors have to have a ratio of 1:10
Smallest value between pin 1 and 3

Most people seem to be happy with 100ohm/1000ohm. (high-ish gain)
(Picture is from .doc in post#41)
Leo..
Attached Thumbnails
MOTU 828 mkII USB crackle-resistors.jpg  
Old 8th March 2014
  #107
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That's a good summary LeeYoo.
Thanks again, you saved my 828's life.
Old 15th May 2014
  #108
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Hi All,

I have a 10-year-old 828mkII (Firewire-only version) exhibiting this mic-pre "crackle" problem and I was wondering; Is it safe to run the unit with the preamp daughter card removed? I don't use those preamps and I don't have time for a fix at the moment...

I do have the inputs muted as a short-term fix, but am worried about cross-channel bleed going on... (haven't noticed anything... yet. Too busy mixing to test.)

Thanks.
Old 15th May 2014
  #109
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Hi 6strings.
I have used the unit with removed daughterboard without a problem.
But why not spend $2 and a bit of time to bring the mic pre to life again.
Leo..
Old 15th May 2014
  #110
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Quote:
Originally Posted by LeeYoo View Post
Hi 6strings.
I have used the unit with removed daughterboard without a problem.
Hi Leo. Thanks for the reply (and all your help here)!

Quote:
But why not spend $2 and a bit of time to bring the mic pre to life again.
Leo..
Yeah, I will for sure when things slow down. I never use those pres (I have outboards with better gain) so I just want the crackle-crackle to stop in the meantime...
Old 24th June 2014
  #111
Thank You LeeYoo. I did the Preamp fix a few months ago and have been enjpoying it. And after spending years trying to read the LCD panel, I finally replaced the LED last night. Soo nice. The Rectangular LED from RadioShack fit pretty nice too.
Rectangular High-Brightness Blue LED Lamp : LED Lamps | RadioShack.com
Attached Thumbnails
MOTU 828 mkII USB crackle-img_20140623_223725.jpg  
Old 16th July 2014
  #112
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Repair crackling MIC potmeters Motu 828 MKII

I had the same crackling issue on the MIC 2 input of my MOTU 828 MKII.
Reading this thread helped me to recognize the root cause, being the gain potmeter. Thanks to LeeYoo and all other who contributed to this. I also searched on the Internet for a replacement type, but was not able to find any close anough. The reliable solution of replacing the potmeter by 2 fixed resistors was a very good alternative, but I started to think about a reliable solution with which you can still adjust the gain. So I tried another aproach using a rotary switch with fixed resistors.
Hope it helps you as alternative.

Following document describes this approach.

Best regards

Erik
Attached Files
Old 16th July 2014
  #113
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Wow...
Solid research and detailed documentation.
Finally a good solution to the problem.

Leo..
Old 20th November 2014
  #114
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Just ordered a resistor kit to try this out - any reason I shouldn't just hook up a small breadboard and have that readily accessible outside of the case for quick value swapping to adjust gain settings? Can I hot swap resistors or should power always be off when changing values?
Old 6th December 2014
  #115
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thanks for your guide Lee Yo , i m just wondering : ' how do i know wether it s the led or the whole display that needs replacing ?
Old 6th December 2014
  #116
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Hi dominique.cologn
If the LED is not working, you can still see the caracters on the display.
Try to shine a light on it.
Leo..
Old 7th December 2014
  #117
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ok i will check that out thanks
also forgot to mention that mine is a mark 3 one.. would it be the same process for replacing the led? same voltages and so forth?
thanks!
D.C.
Old 11th December 2014
  #118
Here for the gear
 

Hi Xonlocust, good idea to use a small breadboard to be able to tune the resistors. I did spent quite some time on iterations in order to define the resistor values. If I should redo it, I should make a breadboard with potmeters, so no need to remove resistors wile defining the values, and no need to turn off the unit while tuning. Did you manage to find a multi position switch with more than 6 positions which fits into the 828? Erik
Old 29th January 2015
  #119
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Finally going to get around to fixing this (I've just had the mic inputs muted to deal with it) and was wondering what watt rating the resistors need to be? I stopped by Radio Shack and they had resistors in 1/4, 1/2, and (IIRC) 1 watt variations?

Also, any recommended online stores for ordering? (RS didn't have pin strips, so I'll need to shop elsewhere)

Thanks.

JP
Old 30th January 2015
  #120
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Hi 6strings.
The power rating of the resistors is not important. 1/4watt is perfect.
Best to use metal film resistors for lowest noise.
Pinstrips are VERY common, and are used on almost every circuit board.
RS has sooo many listed that it's hard to find a plain one.
You must be able to get them in your local electronics store.
http://www.radioshack.com/schmartboa...l#.VMsSkS7Cfao
Break-away 0.1 36-pin strip male header (10 pieces) ID: 392 - $4.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Leo..

Last edited by LeeYoo; 30th January 2015 at 06:20 AM..
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