WTF!!?? Equipment malfuntion ... please help!

[famous beagle]

So I got a Presonus MP20 off ebay. It arrived a week ago or so, I hooked up a mic and tested both channels. Worked like a charm.

Yesterday, I racked it up and tried out the direct instrument input for a bit, and it worked great too.

Then tonight, I was going to quickly test an SM58 before I sell it to make sure it's in good working order. I hook it up, and all goes haywire. I got no level reading until the gain was about 85% up, and then it practically flatlined to the red. I tried different mic cables, different mics, etc. and got the same thing. Then I unplugged the input mic cable altogether and am still getting the same thing.

At first, it was happening only on channel 1, and channel 2 seemed to be ok. But after a few seconds, ch 2 started doing the same thing. And now they're both acting the same way.

When I plug a guitar into the DI input of either channel, it works as normal. But the minute I unplug that, it goes back to the problem on CH1. CH2, however, seems to be "fixed" for a bit, but then, after a minute or so, it starts doing it again as well. This is the case whether a mic cable is plugged into the input or not.

I've attached a sample of the noise that occurs when the meters go haywire. (Don't worry; it's not loud at all.)

Does anyone have any clue as to what could be going on?

Thanks for any help in advance!

 

[Bobbsy]

It could be a hardware fault since you only recently took delivery...but it could equally be a software/driver issue in your computer.

The first thing I'd try would be to download and install the latest drivers for your interface. I'd also make sure to shut down anything else that might be generating sounds or using the sound hardware on your computer--Windows/System sounds for example.

If that doesn't fix things, it may be a hardware issue.

 

[famous beagle]

Thanks for the tips, but I'm 100% certain it is a hardware issue. I can see that I wasn't completely clear in my original post.

When I said the meters were pegged, I meant they were on the MP20 itself---not in the DAW. It's doing this without any signal going in or out (nothing plugged into the inputs or outputs). I just recorded the sound it's making when it's malfunctioning so someone could hear it, in case it's a clue or something. But the problem is certainly within the MP20 itself.

 

[Bobbsy]

Quite possibly but please do try the driver update and shutting down unnecessary audio rubbish on your computer. It's entirely possible to get exactly the symptoms you describe from faulty drivers. Been there, done that, had the noise. The drivers play a big role in controlling what the MP20 is doing, including things like metering--and noise can be caused by something within your computer changing, for example, the sample rate or bit depth without telling you about it. This is a common trick of faulty drivers or having Windows sounds enabled.

Frankly, you have nothing to lose trying the software route--because, if it IS a hardware issue, your options are pretty much limited to returning the MP20 for a refund if your supplier is willing to give one.

 

[famous beagle]

Thanks. I have Windows sounds disabled (and always have), and I updated my drivers in December. But I'll do it again just because I guess.

Like I said, though, unless the drivers in my computer have some telekinetic powers or something, it's not them. The MP20 is doing this all by itself when it's not connected to the computer in any way, shape, or form. It's doing this with only the power cord plugged in and nothing else.

 

[Bobbsy]

In that case the MP 20 has malfunctioned and, if under warranty, needs to be returned. If not under warranty then you're likely out of luck. I suppose you could try cleaning all the pots (or at least turning them back and forth really quickly like you would to eliminate a noisy spot) but that doesn't sound too likely to me.

 

[famous beagle]

Yes, I know it's malfunctioned. It's a 10-year old piece of gear (or something like that), so there's definitely no warranty.

I'm pretty handy with a soldering iron, but I'm not the greatest at troubleshooting. So I was hoping one of the more knowledgeable people on here might be able to help me out with the repair. (I did already try cleaning the pots with de-oxit to no avail.)

 

[Bobbsy]

You said you only bought the pre amp unit a week ago from eBay. If it was an as is sale you have no warranty but, if it was sold as being in fully working order you may well have grounds to return it for a refund--which is a form of warranty.

Unless you're not just handy with a soldering iron but actively enjoy trouble shooting, I'd investigate the return option before your rights run out.

If you decide to hang onto it, the only hint I can think to give you is that, since both channels are affected, you need to start looking at things common to both sides: power supply, mother board (if it's built that way), any linking ribbon cables, etc.

 

[famous beagle]

Yeah ... I guess I was grossly underestimating when I said about a week ago. It was more like a little over two weeks ago. It wasn't sold as-is, but my return window has expired. I made sure to test it before then, and it worked great then!

I don't mind troubleshooting; I'm just not that knowledgeable about mic pres. I've done some work on tube amps and analog guitar pedals, but haven't messed much with this type of thing. Thanks for the tips, though! Hopefully I'll discover the issue.

 

[famous beagle]

Did the seller specify the return window in the ad?

eBay Buyer Protection Policy
"Is there a time limit for a buyer to open a case?
Generally, buyers have 45 days from payment to open a case—the same as with the current PayPal dispute resolution system. Exceptions may be made to buyers based on factors such as member account information, listing information, item location, and shipping method. You'll be asked to work things out with the buyer, but if you're unable to come to an agreement, we won't require reimbursement from you for cases filed after 45 days from payment."

Since the problem seemed to coincide with plugging into the DI inputs I wonder if their is some sort of switching mechanism in the jack to swap inputs or alter the gain and it's dirted up and throws the gain or something out of whack. Same thing with the insert jacks that usually one with have a switch of sorts to "bypass" through the jack when nothing is plugged in. If you are sure you are past any resolution on ebay, maybe a squirt of contact cleaner into the DI jacks and pop the plug in and out a couple times might clean something up. Odd that it happens to both channels unless it's common to both like the power supply. Is the problem occurring on all outputs... single XLR outs, XLR mix out, and the Send jacks?

This was on one of the MP-20's sold on ebay. Not the one you bought is it?
"This unit needs to be repaired. Channel 1 does not work - if it is activated (there is a L/R switch on each channel) there is loud static continuously. Channel 2 works and main outs (left/right) work. Presonus no longer repairs these because they stopped making them a while ago. Therefore, you will need to be handy with electronics and musical equipment to get it working. (I am not familiar with this so I wouldn't even know where to start.) I talked to Presonus and they said it sounds like a part needs to be replaced but they couldn't be more helpful since they no longer service these. Since this unit is only partially working I am selling it AS IS. If you have any questions, please ask prior to bidding."

"Someone suggested I clean the Channel 1 gain pot with contact cleaner and then twist the pot. That cleared up the problem and now BOTH CHANNELS of the unit are working."

No that's not the one I bought. The one I bought was said to be in good working order.

Good news, however! I contacted the seller, and even though it's a few days past the 14-day return window, he's agreed to have his tech repair the unit, and all I have to do is pay for my end of shipping (he'll pay for the return shipping). It's on its way now in a flat rate USPS box for only $16. Can't beat that.

 

[miroslav]

Why not start off by checking/cleaning your connectors with some deoxit cleaner. Then maybe open the unit up (power off)and just take a look inside to see if the wiring from the connectors or any other point appears loose...etc.
Ca-r-e-f-u-l-l-y "poke around" gently touching/checking everything to see if there's anything out of place or that looks odd.
Also...I would then pull any connection inside and apply some deoxit and plug them back in (with power off of course).

Plug a mic in and power it up...and then again, using some non-conductive tool...touch the wires just enough to move them...see if it causes the signal to bounce all over the place.

Just be careful and gentle, and if you perform a systematic overall check...you may find the cause to be something easily fixed or at least isolating it...which will then guide you to a solution.

Otherwise...you can just take it to someone who does that sort of work and let them check it out. It really may be a simple fix.

 

[moresound]

WTF!!?? Equipment malfuntion ... please help!
Thanks for any help in advance!

It could be a hardware fault

Thanks for the tip

The MP20 is doing this all by itself. It's doing this with only the power cord plugged in and nothing else.

In that case the MP 20 has malfunctioned

Yes, I know it's malfunctioned.

Thanks for the tip, though! Hopefully I'll discover the issue.

No that's not the one I bought. The one I bought was said to be in good working order.

This is right out of a Vaudeville act. I got a BIG belly chuckle out of it.



Then the happy ending .....

Ca-r-e-f-u-l-l-y "poke around" gently touching. Just be careful and gentle, check it out.

 

[Bobbsy]

Hey! Gimme a break Henry and check how many posts in it was before the OP actually says the problem exists when disconnected from the computer (which would have been very useful info!).

About 90% of the time, symptoms very similar to this ARE driver related--which is good because that's easily fixable. The OP also didn't give any idea of his technical prowess--for most, as soon as hardware is faulty it's return time. Those with the skills to repair an interface probably wouldn't post in here asking how to do it--if you see what I mean!

 

[moresound]

Yes you are 100 percent correct, Bob.
I just was referring to what I saw within these quotes as being a funnybone tickler for me.

I was going to say just about what you had just said after I posted that ..... I keep forgetting that you guys on the other side of the globe are still up and the sun is shining, While Not but a few of us in the states are still up.

I'll have to type faster!

 

[Bobbsy]

Nah--it's autumn here so the sun went down about 45 minutes ago. Must be time for drinkie poos!

 

[famous beagle]

Hey! Gimme a break Henry and check how many posts in it was before the OP actually says the problem exists when disconnected from the computer (which would have been very useful info!).

About 90% of the time, symptoms very similar to this ARE driver related--which is good because that's easily fixable. The OP also didn't give any idea of his technical prowess--for most, as soon as hardware is faulty it's return time. Those with the skills to repair an interface probably wouldn't post in here asking how to do it--if you see what I mean!

I actually said that (the problem is happening with nothing plugged into the input or output jacks) in my second post (post #3 in the thread). But I always appreciate anyone trying to help, so I would never get bent out of shape about something like that.

I know what you mean about repair prowess. But it's a learned skill. I have some repairs under my belt, but I'm still working on it. I've never worked on something as PCB-heavy as this.

 

[famous beagle]

Miroslav: I did clean the pots and connectors with deoxit. I also opened it up (unplugged) to take a look to see if I saw anything suspicious like a loose connection, burnt resistor, bulging cap, etc. I couldn't see anything.

But when the seller agreed to repair it for only my shipping cost ($16), that was good enough for me. I would probably spend that much in gas getting it to a good repair guy (I live a little ways out from the city).

 

[Bobbsy]

I actually said that (the problem is happening with nothing plugged into the input or output jacks) in my second post (post #3 in the thread). But I always appreciate anyone trying to help, so I would never get bent out of shape about something like that.

Yeah, I saw the reference to disconnecting input and output jacks but interpreted that as the analogue ins and outs, not the connection to the computer. For whatever reason, I never associate the word "jacks" with things like USB or Firewire. Ah well, put it down to a mis-communication.

 

[famous beagle]

Yeah, I saw the reference to disconnecting input and output jacks but interpreted that as the analogue ins and outs, not the connection to the computer. For whatever reason, I never associate the word "jacks" with things like USB or Firewire. Ah well, put it down to a mis-communication.

Oh, well, that was another communication issue too. This is an all analog device; it doesn't have any FireWire or USB jacks. It's just a mic pre---not an audio interface.

 

[PRHunt]

This is right out of a Vaudeville act. I got a BIG belly chuckle out of it.

I was thinking more along the lines of Monty Python...