My Behringer UB802 mixer won't power on - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 33 Old 10-17-09, 03:29 AM
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azuaro
 
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Re: My Behrenger UB802 mixer won't power on

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 ([email protected]) 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

Last edited by azuaro; 10-17-09 at 03:49 AM.
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post #12 of 33 Old 10-17-09, 03:44 AM
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azuaro
 
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Re: My Behrenger UB802 mixer won't power on

This are the transformer specs that I found...

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My Behringer UB802 mixer won't power on-64504.jpg  

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post #13 of 33 Old 10-22-09, 02:25 AM Thread Starter
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Jarrod
 
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Re: My Behrenger UB802 mixer won't power on

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
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post #14 of 33 Old 10-22-09, 06:05 PM
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azuaro
 
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Re: My Behrenger UB802 mixer won't power on

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
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post #15 of 33 Old 11-02-09, 10:58 AM
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Jim
 
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Re: My Behrenger UB802 mixer won't power on

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.
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post #16 of 33 Old 11-02-09, 01:37 PM
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azuaro
 
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Re: My Behrenger UB802 mixer won't power on

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
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post #17 of 33 Old 11-03-09, 09:41 AM
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Jim
 
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Re: My Behrenger UB802 mixer won't power on

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.
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post #18 of 33 Old 11-03-09, 04:36 PM Thread Starter
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Jarrod
 
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Re: My Behrenger UB802 mixer won't power on

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.
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post #19 of 33 Old 11-03-09, 05:30 PM
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azuaro
 
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Re: My Behrenger UB802 mixer won't power on

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
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post #20 of 33 Old 11-03-09, 08:51 PM
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bobdole369
 
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Re: My Behrenger UB802 mixer won't power on

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.
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