DL32R high fq chirping sound audible through case and analog outputs

[bradp015]

This is the weirdest problem Iv seen.

dl32r sn: 204208801BRKF0012
dc16 sn: 204418530BRIY0068
Dante Card
Master Fader app: 5
iPad Pro
netgear nighthawk router

This System is a permanent install at a corporation. I freelance on larger broadcasts and live mix for video broadcasts. Im the only engineer that uses the system other than the director.  Most inputs used and all outputs used for mix destinations. Mixer’s been running very well. Version 5 installed many months ago.
One stereo mix dest. is a NuTek Tricaster.

Recently a high fq chirping signal at about 11k, has shown up at the trickster input. I can see the signal on the DL Tricaster output. Chirping is also present on some other outputs of the DL visually and audibly. Also if you put your head in the back of the rack that contains both audio and video devices along with the DL you can hear an audible chirping. There are no speakers in the rack. So the chirping is audible just by putting your head near the equipment. If you turn the DL power off the chirping no longer is present. Powering the mixer back on the chirping starts. Id think that this is a failing chip inside the DL?
I have unplugged all inputs one at a time. Unplugged all outputs one at a time. Powered down all devices in rack one at a time. Rebooted DL many times.

I recorded 32 chan on the mackie with a usb drive connected to the usb port on the back panel. I do this all the time for shows.
I made sure the input channel that returns the output of the tricaster (this was showing the chirping but soft) was nice and loud so it would be obvious when inspecting it at my studio.
Upon checking the audio files, no chirping on any channel was present.
Channel 1 (a wireless mic which was off) was showing DC @-3.5db in ProTools.
I use the return from tricaster to monitor the tricaster program for quality thru the solo bus. (in in-ear monitors). So it looks to me like the DL’s output is sending the chirping to the tricaster and then i can see the tricaster output on the mackie has the chirping. I first thought the chirping could be coming from the tricaster. But it goes away when powering off the DL mixer.
Im totally stumped why there is no chirping signal on the recording and when looking at the DL you see it on input meter.


Any Idea’s gratefully appreciated!!!

[WK154]

Since you pretty well covered the electronic signal sources I would check fans and or Hard drive of the DL32R if used. Since I know of no electronic signal source of sound (without speakers) that would create a audible sound from the DL32R. Disable fans/hard drive briefly and check for sound. The power supply could also be a source but is harder to test for.
Cheers

[bradp015]

Thanks WK!

We had the installer come to check it out and we both think its either the PS or a chip failing. It's going back to Mackie.

thank you!!!
b

[albundagus1]

So. I have the same issue. The DL32R is not a fun unit to troubleshoot! If the unit is running and operating correctly. The noise is probably coming from an inductor on the main board. On mine, it is the power inductor in the 15+ volt supply which is a 56uH 6 amp SMD inductor (part identifier number L29). The way I was able to troubleshoot this, was to buy breadboard jumpers which has the male on one end and the female on the other.
You will have to pull the preamp board (sits on top of the Mainboard which is under the metal shield. You DO NOT have to leave the I/O board cables attached to the preamp board. When you remove the preamp board off of the IDE PINS, if you power it up, the chirping will be gone.

Use the breadboard jumpers to recreate the IDE pin connections to the preamp board, so you can have access to the Mainboard with the preamp board connected, but out of the way. Start removing jumpers, one by one, until the noise quits. Once it quits, trace out the circuit for the jumper you pulled and you should find the culprit. Usually, only inductors will chirp like that.

[albundagus1]

Just wanted to follow up on the DL32R repair. I replaced the .56uH and the 100uH inductors in the 15+ circuit to no avail! I decided to go back to troubleshooting the 15+ and 15- lines going to the preamp board. Reset jumpers as mentioned in 1st response. Decided to leave the 15+ hooked up and see if it was in the negative 15. When I pulled the + jumpers the sound quit! So, I tried one more thing. I replaced the 15- and unhooked the ground. The chirp was gone! Eureka! It is some where in the ground for the 15+- that is causing the issue. After looking at the schematic, I found a common connection to both inductors and ground on both 15+ and 15-, it was a SMD Electrolytic cap C154 (47uf 25volt) I pulled it and the chirp became a squeal. Checked the ESR on it and it showed open. Replaced the cap, problem repaired. Hope this helps the next person with the problem!

[Weogo]

Hi Brad,

    Do you have the DL32R back from Mackie? 
Did they fine the same problem as Albundagus?

    Albundagus, thank you so much for the troubleshooting notes!
I'll tuck this one away for the future!

Thanks and good health,  Weogo

[bradp015]

Well, Albundagus thats impressive! I am not a elec engineer so I dont usually go into things like that... thank you for the explanation!

Weogo, the director just told me today they are sending the DL back and its fixed. I will try to get the details if i can!


Thank you all for taking a look here at my post!!!

brad p

[smillner]

Just wanted to follow up on the DL32R repair. it was a SMD Electrolytic cap C154 (47uf 25volt), Replaced the cap, problem repaired. Hope this helps the next person with the problem!

Thanks for your follow up!  This was the exact problem we had.  We also had 2 bad caps on the preamp board that we replaced because the top had split open, they were 220uf 25volt, 85 deg caps.  I'm adding some pics and notes to the thread for the next unlucky soul to experience this issue, I surely am thankful for your tracking down the issue, saved me alot of time. 

For the next person:
1. The 2 caps we replaced on the preamp board were soldered on both sides of the board so be very careful not to over heat it trying to get them out, I worked with someone heating and me working them back and forth to get them out, then clean old solder off.

2. If yours is fits the same chirping we had that ramped up on power up and then chirped at 11k then C154 is where I'd start for sure.  It is a surface mount capacitor so there is no need to remove the main board from the mixer.  When you remove the preamp board, you'll see the shield below it (pic attached).  You'll need to unplug all the connections that connect through the shield to the main board and then remove the screws from the bottom side of the mixer to release the shield.  Once the shield is off it's easy to get to C154.  You don't have to disconnect the ribbon cables from the preamp board if you don't want to, just pull them out of the way of the preamp board mounting screws and then you can carefully hang the board over the front of the mixer if you don't want to disconnect them.

Thanks again albundagus1, you were quite a blessing today!

[nate_nisbet@hotmail.com]

Can someone please share the schematics with me? DL32R.
I have the same issue.
I would forever be in your debt!