My Behringer UB802 mixer won't power on

**Jarrod** · **10-13-09, 11:38 PM**

Drat. I've had this for 5 years but have only just started using it last week. All of a sudden it won't power on. I looked in the manual and on Behringer's website where there is passing reference to replacing fuses with the same value fuse. But I can't find a fuse anywhere on this thing.

Any ideas? I know several people here use these, or the newer Xenyx 802.

**azuaro** · **10-14-09, 12:49 AM**

Hello,

Start by checking voltage on your power supply before anything else....If there is power, then check the power switch. If both are OK, then follow the power (+) on the circuit board after the power switch and if there is a fuse you should be able to find it.

Most times than not the power supply is the part that fails but you may have another issue...Please let me know how you did...

Best regards,

AZUARO
Flathead lake, MT

**Jarrod** · **10-16-09, 09:00 PM**

Thanks. It is the power supply that's gone bad. Pity. I am waiting to see if Behringer will do anything for me (I really think they should - this unit has less than 20 hours on it!) Otherwise, I can order a replacement from dbmproaudio.com for $15 +ship.

**azuaro** · **10-16-09, 11:57 PM**

I agree...It is really aggravating when a piece of equipment fails this soon...

The MXUL5 Power supply that you have is a 110-120 VAC to 17.5 VDC with I believe 650 mA ...Most of these new power supplies are made in China and a generic adaptor will also work fine...Don't be limited to getting the original part as they are usually much more expensive...Don't spend much more than about $15-20 dollars because you can get a new UB802 for well under $40.00.

As an example, go to hosfelt com on the internet and select APTERS 14-18 VDC. There is a filtered power supply with 17 VDC and 1.5 amps that will work in your Behrenger for $7.95 plus shipping and there is another one that will provide 18 VDC and 1 Amp for $4.95 plus shipping (Better choice)... The one that provides exactly 17.5 VDC it way more expensive...

Get on the internet and Goggle AC-DC Power supplies and look for a filtered power supply (For less noise) with 17-18 VDC output from 110-120 VAC and with at least 650 mA...More mA will be OK so don't try to get exactly 650 mA.

If the connector for the adaptor you get doesn't match the input of your UB802, you can always cut the cable on the bad power supply and attach it to the new one.

Good luck and best regards,

AZUARO
Flathead Lake, MT

**azuaro** · **10-17-09, 12:26 AM**

I forgot to ask you to test the cables on your Power Supply...Many times the problem is that the cables are cut inside the jacket...

This is an old trick for not having to cut the cables for testing and you need to do it carefully...Get a couple of pins across the cable jackets on the + and - sides just at the exit of the PS block, make sure that the pins don't touch (short) and then connect the PS to the AC outlet and with a voltmeter measure for DC power at the pins. If there is power, then the problem is somewhere along the DC output cables...

If you get DC power at this point, then check (same process) just before the connector that plugs into your UB802...If you get DC power but you are not getting power at the connector, then then the problem is the connector.

If you don't get DC power out of the PS block, then measure for AC current just before the cables merge with the body of the Power Supply...WATCH OUT because here you are dealing with AC current and my advice will be to get the pins across the jacket and into a scrap piece of wood (like nailing it to the wood) so the pins don't move and it is better if you do both sides about 3-4 inches apart so there is no risk of touching and shorting....Make sure that you don't touch the pins either and of course, use common sense and do this at your own risk.

I have seen many power supplies that failed because the AC plug is defective, because the AC cables before the DC transformer are damaged and because the DC cables after the PS body or the outlet plug are damaged...Test each and every point and component and replace as necessary, many times you can repair these PS units for no cost at all.

Best regards,

AZUARO

**Jarrod** · **10-17-09, 12:52 AM**

This mixer uses the MXUL3 power supply that converts 110V AC power to 17.5V AC at 250mA. That's not a typo - the UB802 runs off 17V AC power. Quite a strange setup.

Interesting idea about testing the cables. So you literally mean to use pins, like sewing pins to penetrate the cable near the exit of the brick and then use those to test for continuity and/or AC voltage?

**azuaro** · **10-17-09, 01:40 AM**

I am always kind of reluctant to suggesting Old Yankee Ingenuity or engineering because nowadays there are many more options and younger generations are spoiled and not used to repairing anything...We live in a use and discard world, at least here in the US but the rest of the world is still different...

There are voltmeters and equipment that can measure current, voltage, etc. thru the jacket but most of the people out there have plain not so expensive multi-meters that need to be touching the bare metal of the cable without a jacket for giving a reading...

When I was a student at MIT back in the late 60's, we used fine sewing needles for what I am suggesting, this was as common as using your voltmeter...A fine needle will make contact with the metal strands of the cables thru the jacket without cutting or disturbing them, and as soon as you remove the needle the jacket pretty much seals back leaving your PS as it came from the factory...If your needle was thick, well, then use a drop of nail polish on the little hole around the jacket for sealing it back...

Push the fine needle thru the jacket at the center of the cable, this will extend the contact surface of the metal strands of the cable to the outside the jacket so your voltmeter can function....Do this wherever you want to test for voltage (either AC or DC) or for continuity...Take very special care when measuring AC current.

If your PS is 17 VDC and 250mA, then the one that costs $4.95 at hosfelt.com (see my post above) will do a perfect job in case your PS is unrepairable.

Best regards,

AZUARO
Flathead Lake, MT

**Jarrod** · **10-17-09, 01:51 AM**

Nice ideas. I just tried this and the cable looked OK. So I decided to go ahead and take the transformer out of its plastic box and measure directly there. Bad news, there is no voltage across any pair of the three tabs coming off the output coil.

Thanks very much for your advice!

**azuaro** · **10-17-09, 01:56 AM**

Well, at least you found that it is the inside what is wrong and you know how to do it if it ever is necessary...

Go to the website that I mentioned in my previous post(s) or look for another supplier on the internet and buy a generic filtered 17 VDC -250 mA or more (for less noise) Power Supply...

Regards,

AZUARO
Flathead Lake, MT

**Jarrod** · **10-17-09, 02:10 AM**

Yeah I was just looking at hosfeld as per your advice. The original PS says this:

output 2 * 17 VAC / 250mA

There is an 18 VAC adapter there (Basler BE114720CAA) that might work if I knew the pinout of this cable. The Behringer tech support person I talked to this morning did not have the pinout....all I know is that two of the three pins have +17 VAC and the third pin is common ground.

I can't use an AC-DC adapter in place of the original AC-AC adapter can I? Or are you just saying that other Behringer mixers use DC power?

**azuaro** · **10-17-09, 04:29 AM**

I am sorry, I missed the ball while trying to answer a couple of posts at the same time and I think that I confused you more than I helped... I don't have a Behrenger mixer but I do have 3 Behrenger pedals that are almost identical to the Boss and they use PS supplying 9 VDC; this is where I lost track of your needs...

An AC to DC converter is not what you need, your MXUL3 Power Supply has 2 outputs that are 18.5 V (AC) and 150 mA so you need an AC to AC transformer with two 18.5 volt AC outputs rated at 150mA or more each...

I found a picture from the actual MXUL3 PS (Posted below) and this tells me that indeed the pins are two 18.5 VAC and 1 common ground. Unless there is something I don't know about the mixer's internal circuit, I don't see why you can't use the 18 VAC - 1100 mA transformer that is listed at the Hosfelt site for $2.49 http://www.hosfelt.com/contents/en-us/d19.html

The specs of the MXUL3 that I found are a little different than yours, this model I found has two 18.5 V at 150 mA....In either case I am almost certain that the transformer listed above should work fine...

One last point, I wish we knew if the 802 needs a regulated and/or filtered PS or not, because of the cost of the 802 I assume it doesn't but please check your manual and see if it says something about it....Whenever you are dealing with sound, filtering for reducing noise and regulated Power supplies are to be considered.

If you have a circuit diagram for the mixer (sometimes included with product's documentation) please email it to me (azuaro@icehouse.net) and then I will be able to tell you more accurately what is going on and what is that you need.

I have some doubts

about why 2 outputs with the same voltage but I suspect that one of the outputs is supplying power to a separate circuit inside the mixer for doing another function (Like amplifying the voltage for a Phantom PS in order to power a microphone or something else) while the rest of the mixer is using the other 18 VAC input for normal operation.

Hopefully this will make it up for the mix up....Sorry once again...

Please let me know...

Best regards,

AZUARO
Flathead Lake, MT

**azuaro** · **10-17-09, 04:44 AM**

This are the transformer specs that I found...

**Jarrod** · **10-22-09, 03:25 AM**

Yeah that one in the picture is slightly different from mine. Same model number but the Behringer engineer that I spoke with on the phone mentioned that the one I have is an older design and that they have changed this PS since then. That should tell me something about what they thought of the original design

I found a block diagram for the UB802 in the box. I don't think this has what you would need to figure out the power config - it only looks like it covers the audio connections themselves. I'll scan it and send it if you think it is useful.

In the meantime, I went ahead and ordered a direct replacement for $15+shipping from dbmproaudio.com. I am interested in trying to figure out how to get this one from hosfeld to work but I needed something quick in the meantime. Maybe we can reverse-engineer it when it arrives

**azuaro** · **10-22-09, 07:05 PM**

Good to hear that you will be resolving this issue with a new PS...Nothing like suing original parts for peace of mind...

Measure both outputs of your new PS, I am almost 100% certain that the 2 outputs are connected in parallel from the same transformer and if this is the case the PS from Hosfeld will work very easily.

If there were issues affecting sound or other functions of the UB802 caused by radical changes in amperage, such as the use of a 48V or more (Phantom PS) the company could be using 2 separate PS inside the same transformer box for convenience and this issue would then be resolved with 2 of the Hosfeld transformers....

I really don't anticipate this factory PS to be as described above and I think the 2 parallel outputs with the same voltage and capacity are there for convenience and easiness of circuitry inside the UB802 in order to keep costs down. It is easier, cheaper and better to isolate the circuit for a phantom transformer inside the UB802 than it is to do it in the transformer itself.

If there is anything else where I can be of any help, please let me know...Enjoy your UB802...

Best regards,

AZUARO

**jimfrank** · **11-02-09, 11:58 AM**

I've built jerry rigged adapters for this type of dual AC power supply. Mine was for a different brand of mixer, but same idea. I used a center tapped 25 volt transformer on a variac to get two phases of 18 volts to run the mixer until the real supply arrived in the mail.

**azuaro** · **11-02-09, 02:37 PM**

It is great to hear that!...A little creativity and Yankee engineering are always helpful...

My only concern about suggesting what I did was that I don't know if the original PS has a noise filter of some kind given the fact that it is dealing with sound; I was not able to find the diagram but if there is one, I suppose that it may very well be inside the mixer box.

Anyhow, It is always good to hear that somebody resolved a problem...

Regards for all members...

AZUARO
Flathead Lake, MT

**jimfrank** · **11-03-09, 10:41 AM**

I did put an MOV (130V) on the input AC lines, and bypassed both lines to ground with small value ceramic caps to shunt transients. That's all that's really necessary, the mixer makes the bipolar DC and filters it.

**Jarrod** · **11-03-09, 05:36 PM**

You guys' electronics chops are waaayy out of my league

Maybe I'll take the dead transformer apart again and post some images for others to see in case someone else runs into this issue in the future. It is apparently not all that uncommon an issue on this model. It may be an easier fix to find a replacement for the internal transformer itself. I *think* I ran across one when searching before, but didn't bother to save it because I wouldn't have known how to wire it correctly anyway.

**azuaro** · **11-03-09, 06:30 PM**

Jim, It is good to know the configuration of these PS ...Thank you for posting it, I have tried hard to find a schematic without any luck...Your approach makes very good sense...

Jarrod, you seem to be the right intuitive person for doing some experimentation on your own...Get a multimeter and buy one of those transformers that I mentioned in my previous posts (Hosfelt), they are very cheap and work very well...You can fix your problem and have a much better & sturdier unit than the original PS for 5-8 US assuming that you will do what you are mentioning about reusing some internal components...

If the factory PS units fail very often, then maybe it will be worth installing a simple fast acting fuse, it could be done very nicely with a fuse holder integrated to the PS box for easy replacement...Then the power spikes would be a fuse issue and not a PS replacement issue...

If the factory doesn't do it, it is because of saving money not because it is not needed.

Good luck with your project and just watch out whenever you are dealing with AC current ...

Regards for all members.

AZUARO
Flathead Lake, MT

**bobdole369** · **11-03-09, 09:51 PM**

I just picked up a UB802 for a great bargain - no AC adaptor. Luckily I'm versed enough to make it work. The unit powers up and works just fine with the same 18.5V rail on both inputs. However just as an exercise I'm intending to build an SG2525 based forward boost converter to go from 12V -> 2x 18.5V, just as an exercise in learning.

**glaufman** · **11-03-09, 10:14 PM**

Quote:

bobdole369 wrote:

I just picked up a UB802 for a great bargain - no AC adaptor. Luckily I'm versed enough to make it work. The unit powers up and works just fine with the same 18.5V rail on both inputs. However just as an exercise I'm intending to build an SG2525 based forward boost converter to go from 12V -> 2x 18.5V, just as an exercise in learning.

Should be fun

Quote:

jimfrank wrote:

I did put an MOV (130V) on the input AC lines, and bypassed both lines to ground with small value ceramic caps to shunt transients. That's all that's really necessary, the mixer makes the bipolar DC and filters it.

Is that 130V RMS on the MOV? Ceramic caps won't do much for transients... anything substantial will run the risk of blowing them... also, MOVs deteriorate with each time they fire...

**jimfrank** · **11-04-09, 10:42 AM**

Yes, 130 RMS- a GE MOV designed for 120VAC surge suppression. Ceramic caps are intended to have a low impedance for signals at very high slew rates (RF or other fast spikes) and it would take a sustained dose of high frequency input to damage one. I've never seen a cap go out in this duty, although I have seen MOV's break down. The cap helps protect the MOV by shunting some energy before the MOV conducts.

**glaufman** · **11-04-09, 08:18 PM**

I was more concerned about overvoltage on the cap... but I think I see now, the MOV helps protect the cap which in turn takes stress off the MOV... I guess that'll work the first time, but as I said, there's reams of data showing that after the first hit the MOV fires at a different voltage the second time... I guess you're mitigating the effect somewhat, but it's absolutely inevitable.

**Speedskater** · **11-05-09, 08:35 AM**

It's probably a bad idea to connect either MOV's or capacitors from the AC power lines to the ground. ExactPower has a white paper "The Truth" on page 14 the explain exactly why it's a bad idea.

**jimfrank** · **11-05-09, 11:46 AM**

"It's probably a bad idea to connect either MOV's or capacitors from the AC power lines to the ground. ExactPower has a white paper "The Truth" on page 14 the explain exactly why it's a bad idea."

I just downloaded the paper, and it's page 17 in the latest edition... However, I don't see what their objection is, exactly, as every surge protector and power strip with integrated surge suppression uses exactly this technique.

As far as over voltage on the cap, I usually use 600V caps. It's a very common voltage rating for small ceramics. Any signal over that voltage is very likely to be the edge of an inductive kick back somewhere, and won't last for more than a few microseconds.

Nearby lightning strikes call off all bets.

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