Altec MX6021

[lincolnkorg]

Re: Altec MX6021

Thabk you Momaka and Behemoth.

So its safe to leave the those SMD caps as they are. Im learning and this is great knowledge to have.

To reduce the cost, im going to the local market this weekend to source as many components as I can and then order the rest from Aliexpress or UTSource.

Thanks so much once again folks for the inputs and help. Much appreciated.

[Behemot]

Re: Altec MX6021

Film caps, especially axial, do have prefered orientation though (good for audio circuits).

[momaka]

Re: Altec MX6021

You're welcome!

Do SMD caps have polarity? C25 is the SMD in question.

No, ceramic caps (be it SMD or regular through-hole), as well as film caps (polypropylene, polyester, etc.).... do *not* have polarity.

Only electrolytic and Tantalum caps have polarity.

Also im not sure the 4 SMD resistors are of the right values. A picture posted here showed those resistor values as 1R00. The value of the ones on the board read 1002.

Measure across them and multiply that reading by 4 (since there are 4 in parallel, the resistance will be 1/4 of the printed value on each resistor)... though chances are your multimeter probably won't be able to measure that low (0.25 Ohms, if they are all 1 Ohm resistors, as the value 1R00 would imply).

[lincolnkorg]

Re: Altec MX6021

Here are the pictures of the secondary side.

[lincolnkorg]

Re: Altec MX6021

Thank you so much Momaka.

I will follow the steps you mentioned. Will take a while for to source all the spares and get them shipped. I will attach pictures shortly.

A couple questions. Do SMD caps have polarity? C25 is the SMD in question. Also im not sure the 4 SMD resistors are of the right values. A picture posted here showed those resistor values as 1R00. The value of the ones on the board read 1002.

Thank you so much once again for taking the time to go through the pictures and giving dicrectuons from where to start. Ill remove the components in question and clean the board while i wait for the parts to arrive.

[momaka]

Re: Altec MX6021

Oh boy, where to begin here....

Here's a "short" list
1) The primary cap looks bulged (and you said it is), so that needs to be replaced.
2) Anywhere you see black sooth or burn marks - clean it up well with IPA (Isopropyl Alcohol). Black sooth like that can be conductive.
3) Right in front of transistor Q2, there is a small blue capacitor with what appears to be brown/black glue - remove all of this glue, because it is bad (it goes conductive with heat)
4) Top left corner of this picture, you have some lifted traces. Probably best to remove the coating on top of it and coat it all with solder. Make sure the trace is continuous throughout.
5) Top center of same picture above, you can see some SMD resistors badly soldered - check those on your multimeter. They should appears as a very very low resistance reading (probably even short-circuit).
6) Replace caps C11 and C14 on the primary side.
7) Post a picture of the secondary side... and also probably a good idea to check the secondary side output rectifier(s). Replaced the caps too, if they look or test iffy.

If you decide to test the power supply (I suggest doing that without connecting it to the rest of the Behringer unit), attach a incandescent light bulb (60-100W) in series with the line cord. This will limit the current if there is something wrong with the power supply, so that you don't end up blowing out Q2, the main fuse, or any other components. Here's a diagram how to connect the bulb as well as what to expect, in case you're not sure:
https://www.badcaps.net/forum/showpo...4&postcount=70
... if the bulb stays lit for more than a few seconds on your power supply, you have a short-circuit or faulty component somewhere (most likely the primary side).

I also noticed that C25 was mounted in an angel, wondering if this was tampered by the previous person who tried to fix it. The polarity of C25 is reversed (smaller reading on diode test on one side and bigger reading when the probes are reversed, not sure if this is the right way to test) when compared to C24. Does that matter? Should I reverse C25 to match C24?

Don't reverse the polarity of any capacitors without knowing first which is the correct way they should be installed.

If you look on the PCB, you will see that each electrolytic cap has a "+" symbol next to one of its sides - this is the positive side of the cap. The negative side of the cap (i.e. the side with the stripe on the cap) should be opposite of that.

[lincolnkorg]

Re: Altec MX6021

Hope these pictures help.

[lincolnkorg]

Re: Altec MX6021

Thank you for your reply Agent24, I will take some pictures of these parts and post them in the evening. Thanks so much once again, much appreciated.

[Agent24]

Re: Altec MX6021

Can you post photos showing these parts especially C25?

You can't test capacitors in diode test mode except for a short so the results are meaningless.

[lincolnkorg]

Re: Altec MX6021

Has anyone had success in repairing the power supply? I am a hobbyist, got a unit from a friend to fix. Someone has already tried working on the board earlier.

So far from what I've tested, the fuse, rectifier diodes, mosfet, the 4 SMD resistors at the bottom, filter cap (bulged on the top) seems to be the problem. Do zener diodes need to be replaced? Does anyone have all the part numbers? What else could have failed along the way.

I also noticed that C25 was mounted in an angel, wondering if this was tampered by the previous person who tried to fix it. The polarity of C25 is reversed (smaller reading on diode test on one side and bigger reading when the probes are reversed, not sure if this is the right way to test) when compared to C24. Does that matter? Should I reverse C25 to match C24?

Any insights would be of great help.

I haven't tried to power the unit yet, the area around the fuse looks a little burnt.

Thanks in advance.

[ant3202]

Re: Altec MX6021

Ahhh finally someone has a decent pictures, seems this power board is failing.....

my infineon mosfet seems to be shorted, all beeps ....

[naveenbedre]

No.
They have different pinout and made for different circuit.

Thanks

[zerbino]

Re: Altec MX6021

Bought NCP1351D at this place.

[naveenbedre]

No.
They have different pinout and made for different circuit.

Thank you for reply

[zerbino]

Re: Altec MX6021

Hello, guys.
I personally could not repair the breakdown, so I gave it to the service center. The specialist told me after the repair that he replaced the "some kind of diode" and it all worked. Although before this I replaced 1 transistor near C3, and 4 resistors 1Ohm and a capacitor. But I did not have enough the mind and knowledge to diagnose and understand that there is also a diode out of order. By the way, it was not necessary to replace U1. It was working, as well as the rest of the resistors.
Thanks to all.

[Agent24]

Re: Altec MX6021

Get the NCP1351D from UTSource, that's probably your best option for cheap. https://www.utsource.net/sch/NCP1351D

MOSFET blows up and takes out the controller, usually.

I'd suspect the glue caused the MOSFET failure. Remove all of it. Heating it with hot air makes it easier to get off.

[momaka]

Re: Altec MX6021

U1 1351D PATM can i replace with UC3842

No.
They have different pinout and made for different circuit.

[naveenbedre]

Re: Altec MX6021

U1 1351D PATM can i replace with UC3842

[Th3_uN1Qu3]

Re: Altec MX6021

If U1 fried, quite possibly it would fry the transistor again...

Indeed. When you have a switching mosfet short circuit, connected to a controller chip with low (under 100 ohm) or no gate resistance, it is recommended to replace both switching transistor and controller chip together. This is valid for all switching power supplies.

I once blew 2 sets of mosfets and 3 charge control chips in an Acer laptop which had a no battery charging fault. The final time i replaced both the mosfets and the charge control chip and everything worked fine then.

[eccerr0r]

Re: Altec MX6021

Does the DBT bulb turn on and stay lit if the transistor isn't in the board?

If so - look into diode or main capacitor shorts.
if not, then suspect feedback, U1, transformer, or output.

If U1 fried, quite possibly it would fry the transistor again...