Behringer F1320D Floor Monitor (300W)

[welldigger99]

Hi Guys,
I need to replace the dual rail power supply in this unit (board damaged irreparably - by me!).
I have the schematic (attached) - but it does not (unhelpfully) show the value of the Pos and Neg rails.
Someone has suggested possibly + and - 42V, but as the smoothing caps are only rated at 50V this could be a bit close to the mark.
I am hoping Alxxxxpress might be able to come to the rescue and I am thinking somewhere in the 32V 8A region? Any suggestions/observations would be welcomed.
Many thanks.

[momaka]

According to the specs of the F1320D, it is rated for 160W RMS into 8 Ohms for the woofer. To get that kind of power into 8 Ohms, the dual supplies need to be at least +/-51V... but that's only if the amplifier is configured as single-ended (i.e. one side of the speaker is grounded / connected to common, while the other side is connected to the amp.) Since your caps are only rated for 50V, I think we can rule out that the woofer amplifier is in single-ended (half-bridge) configuration. More than likely, it's configured in bridge-mode (full bridge) - i.e. both terminals of the speaker are driven by two (class D) amplifiers. To get 160W RMS from these, you then only need half the voltage stated above. So chances are, the original supplies were probably closer to +/-25V... and I suggest to start with that and then go up, if needed. If you can get the part number of the woofer amplifier IC(s), that would be even better, as then we may be able to get a datasheet and figure out what the maximum allowable voltage of the IC is.

The next issue would be where can you get dual output (+/-25V) supply like that. Apart from going "oldschool" here and looking for a regular line transformer with center-tapped (18-0-18V) outputs, I think the search for dual SMPS with the above voltages might be difficult. Also 25V is not too standard. However, 24V is relatively standard. So perhaps you might be able to find a +/-24V SMPS? The slight drop in voltage will lower the max RMS output power level to about 144W, though.

As for current rating, 160W RMS into 8 Ohms comes out to about 4.5 Amps - that would be the continuous rating. The peak current draw can be as high as a little over 6 Amps (300W peak into 8 Ohms). So if you are gonna go with an SMPS, I'd say pick something that can do at least 6 Amps continuous, just so that it doesn't trip during high transients. Also, assuming the class D amp(s) have 90% efficiency, you might need to increase that to 7 Amps. And if this PSU is both for the LF and HF amps, then add another 3.33 Amps, bringing the total to around 10 Amps.

Anyways, good luck with the PSU hunting on Ali! You could also get two 24V PSUs and wire them in series to get +/-24V output. The only problem with doing that, however, is if the PSUs don't come On at very very close to the same time, as this can sometimes upset the speaker voltage offset detection and put the amp(s) in protect mode. I just ran into this exact issue fixing a subwoofer amp, since I didn't have a dual-output transformer and instead used the single output into a voltage-doubler circuit. Depending on if the positive or the negative cap got charged first, sometimes the woofer would turn on and work OK, and sometimes it would just sit there in protect mode until I unplugged it and let the caps drained, then power it on and try again. So TLDR: the series PSUs might not work sometimes. In my case, I subbed the single-output transformer with two 20V laptop adapters and found that if the negative supply comes before the positive, the offset protection would not kick in and everything worked OK. So I had to find which of the two adapters had its output come on before the other to wire them correctly.

By the way, what's wrong with trying to fix the original PSU? Can we see the damage? You have the schematic, so even if the original board has a lot of burned traces around the controller, you could always rebuild that onto a new perf. circuit board and then run wires back to the original board.

[CapLeaker]

What makes this PSU not repairable?

[welldigger99]

Thanks momaka, for your very comprehensive and helpful reply. Here are the before and after pics! (in response to Capleaker also).I'd really like to attempt a repair along the lines of what you have suggested, but you may change your mind about the viability when you see the extent of the damage!

[madan1]

The attached schematics look similar to B112D, which uses for AMP TDA8954TH, and that TDA is rated to +/-41V.

[madan1]

Thanks momaka, for your very comprehensive and helpful reply. Here are the before and after pics! (in response to Capleaker also).I'd really like to attempt a repair along the lines of what you have suggested, but you may change your mind about the viability when you see the extent of the damage!

I've seen worse. You can try using a universal daughterboard for the IC and run wires from it (p.s. as suggested above).
According to the local parts shop, FAN6300ANY can be used as a replacement, and it can be purchased in dip-8 package, that gives you more material to solder to.

[CapLeaker]

I've seen much worse than that. There are a few ways to attack this. You'll be surprised what carnage I get. How bad is it? Repairable on my bench. You got to cut all that black burnt carbon crap out and then put a PCB in the hole, redo some traces and Bob is your uncle, if you know the missing parts.
Or Google: Behringer SMPSU32 and you buy a full replacement for 108 bucks.