Kiwi Ate Half of My DMP-3?

[coloradojay]

Has anyone ever had a mic cable eat a preamp? Maybe an intermittant short?

I've had some cheapy cables die, or get stratchy, but they never took any gear down with them... ...maybe until now...

So the setting is: I've set up 4 mics to record scratch tracks with my band, I've got my 012s running into my DMP-3 (with phantom power), one for the drums, one for the guitar amp (at about 2 feet). I look over and the guitar player decides he's going to try to put the 012 right up on the grill, and in doing so stretches the BLUE Kiwi mic cable super-tight between the mic, and whatever it's caught on over at my desk. I'm like "dude!, careful, that's like a $40 cable and you are stretching the crap out of it!!!" So he relaxes the cable back and puts the mic back where I had it, and all seems good. ...Until I go over to adjust the gain, and now I've got a dead channel where I was recording just fine with the same mics as overheads the day before. WTF?

So after some testing I figure out that channel B of my DMP-3 is now cooked. It's still got phantom power, just no gain. I tried the 012, and cable on the good channel, and it works fine. My cable cop says the cable is fine, but I just can't bring myself to trust it and risk eating anymore pres. Crap. Should I just trash the cable? I haven't had a chance to open the DMP up yet to see if I can trace out anything that cooked, and it doesn't look like it's got any fuses, at least externally accessible ones.

Did the DMP just crap out on it's own, or did the Kiwi eat it?

Anyone know where I could get a schematic for the DMP-3?

 

[heroics321]

I'm guessing it pulled something loose on the board. I've never opened one up, but I'd imagine the XLR's are board mounted on that piece. Open it up, wiggle some stuff around, look for broken solder joints, I really doubt it's the cable.

 

[Juggernaut]

Hehe

When I read the title I imagined a kiwi like pac-man (kiwi the fruit) eating your pre amp...

Other than that I have nothing constructive to say...

 

[ocnor]

Hehe

When I read the title I imagined a kiwi like pac-man (kiwi the fruit) eating your pre amp...

Other than that I have nothing constructive to say...

I thought maybe he had a dog named Kiwi. My black Lab would eat a DMP-3 if given half a chance. She tore into my Christmas decorations and chewed them to smithereens.
No help here either.

 

[dgatwood]

I'm guessing it pulled something loose on the board. I've never opened one up, but I'd imagine the XLR's are board mounted on that piece. Open it up, wiggle some stuff around, look for broken solder joints, I really doubt it's the cable.

Unless the phantom ties in with a different solder lug on the XLR connector, that seems unlikely, unfortunately. More likely that the board is cracked. If you don't see any fractures in the board, though....

If the input is transformer-coupled, and if the phantom power were shorted to ground, and if the signal ground were not properly grounded, you could deliver 48v to an input. That's the only way I can think of that you could possibly damage an input by shorting it out. An output, sure... but an input... no. Normally, ground on an input is equivalent to no signal....

Here's the chipset spec on the amp chip reportedly used in the DMP3.

http://focus.ti.com/docs/prod/folders/print/ina163.html
http://focus.ti.com/lit/ds/sbos177d/sbos177d.pdf

Note Figure 5. If that's the way they wired it, I don't see any way that a short to ground could cause a failure of the preamp.

Flip side of that is this forum post where they basically describe how to build the DMP3 for under $50.

http://studio-central.com/phpbb/viewtopic.php?t=9114&start=0&postdays=0&postorder=asc&highlight=

 

[coloradojay]

Pretty sure there are no Transformers in the DMP (it's too cheap to afford them). Thanks for the info. With any luck it is something simple like a bad solder joint or perhaps even a cracked board, I can bridge the traces back together on.

Thanks for the links to the chip specs, at least I'll know how it's biased, and can do some basic testing to see where there is and isn't signal being passed and probably narrow it down.

Unless the phantom ties in with a different solder lug on the XLR connector, that seems unlikely, unfortunately. More likely that the board is cracked. If you don't see any fractures in the board, though....

If the input is transformer-coupled, and if the phantom power were shorted to ground, and if the signal ground were not properly grounded, you could deliver 48v to an input. That's the only way I can think of that you could possibly damage an input by shorting it out. An output, sure... but an input... no. Normally, ground on an input is equivalent to no signal....

Here's the chipset spec on the amp chip reportedly used in the DMP3.

http://focus.ti.com/docs/prod/folders/print/ina163.html
http://focus.ti.com/lit/ds/sbos177d/sbos177d.pdf

Note Figure 5. If that's the way they wired it, I don't see any way that a short to ground could cause a failure of the preamp.

Flip side of that is this forum post where they basically describe how to build the DMP3 for under $50.

http://studio-central.com/phpbb/viewtopic.php?t=9114&start=0&postdays=0&postorder=asc&highlight=

 

[coloradojay]

Yup, sounds like a good troubleshooting path. Just got to get the time to tear it apart.

I'm guessing it pulled something loose on the board. I've never opened one up, but I'd imagine the XLR's are board mounted on that piece. Open it up, wiggle some stuff around, look for broken solder joints, I really doubt it's the cable.