M-audio AV30 speakers recap and repair

[SnowKitteh]

my roomie got a set of AV-30s that someone was just gonna throw out cause they didn't work. i popped em open to take a look, and sure enough there were a few obviously vented caps, and a few that had the labels toasted up by a zener diode that exploded. the capacitors were lxon brand (i think... kind of hard to read the font on them) after replacing all of the electrolytics, (except for two 1uf 50v nonpolarized ones near the bass boost switch, i accidentally ordered polarized ones and didnt wanna swap the wrong kind in.) two ceramic caps that looked discolored from heat and two zener diodes, one of which exploded and left some nice burnt traces on the bottom of the board for me to repair i was finally able to hook them up for a test run, the job was a success and they pump out decent sound for a small set of speakers. unfortunately, i do not have any pics of the damage or the repair because my camera takes grainy out of focus pics of small stuff like that.
wheeee, first post (long time lurker though)

[ben7]

Re: M-audio AV30 speakers recap and repair

my roomie got a set of AV-30s that someone was just gonna throw out cause they didn't work. i popped em open to take a look, and sure enough there were a few obviously vented caps, and a few that had the labels toasted up by a zener diode that exploded. the capacitors were lxon brand (i think... kind of hard to read the font on them) after replacing all of the electrolytics, (except for two 1uf 50v nonpolarized ones near the bass boost switch, i accidentally ordered polarized ones and didnt wanna swap the wrong kind in.) two ceramic caps that looked discolored from heat and two zener diodes, one of which exploded and left some nice burnt traces on the bottom of the board for me to repair i was finally able to hook them up for a test run, the job was a success and they pump out decent sound for a small set of speakers. unfortunately, i do not have any pics of the damage or the repair because my camera takes grainy out of focus pics of small stuff like that.
wheeee, first post (long time lurker though)

Good job, and, lucky for getting off with such an easy repair!

[SnowKitteh]

Re: M-audio AV30 speakers recap and repair

ack, won't let me edit my post. made a typo on the two caps i didn't replace, they were 0.47uf, not 1uf. does anybody know if i could replace them with ceramic caps since they are nonpolarized?

[Th3_uN1Qu3]

Re: M-audio AV30 speakers recap and repair

Ceramics in audio path = bad idea. You can use polypropylene or polystyrene.

[SnowKitteh]

Re: M-audio AV30 speakers recap and repair

Ceramics in audio path = bad idea. You can use polypropylene or polystyrene.

any recomendations? i might replace those two caps later. also, i mostly used nichicon and panasonic caps for the others. (the pannys were i think FC and FR series? got em off mouser.)

[Top Fuel]

Re: M-audio AV30 speakers recap and repair

my roomie got a set of AV-30s that someone was just gonna throw out cause they didn't work. i popped em open to take a look, and sure enough there were a few obviously vented caps, and a few that had the labels toasted up by a zener diode that exploded. the capacitors were lxon brand (i think... kind of hard to read the font on them) after replacing all of the electrolytics, (except for two 1uf 50v nonpolarized ones near the bass boost switch, i accidentally ordered polarized ones and didnt wanna swap the wrong kind in.) two ceramic caps that looked discolored from heat and two zener diodes, one of which exploded and left some nice burnt traces on the bottom of the board for me to repair i was finally able to hook them up for a test run, the job was a success and they pump out decent sound for a small set of speakers. unfortunately, i do not have any pics of the damage or the repair because my camera takes grainy out of focus pics of small stuff like that.
wheeee, first post (long time lurker though)

Hey Bud . I am up agaisnt the same problem . What is the value of the 2 caps by the zeners . I think they are 22 uf , not sure . What is the voltage on those two zener diodes . If i get that figured , I'm up and running . Many thanks bros.

[Top Fuel]

Re: M-audio AV30 speakers recap and repair

The caps in question are the electrolytic ones

[fcda]

Re: M-audio AV30 speakers recap and repair

Also trying to repair a set of these. On mine the zener diode Z1 has burnt out, and the electrolytics C48 and C47 (220uf 25v) look suspect. There's another zener (Z2) and a couple of ceramic caps (C4 & C10) nearby which I'd also like to replace.

Does anyone know of suitable replacements for the zener diodes and the ceramics?

A pic (not detached the board from the back plate yet):

[ben7]

Re: M-audio AV30 speakers recap and repair

Also trying to repair a set of these. On mine the zener diode Z1 has burnt out, and the electrolytics C48 and C47 (220uf 25v) look suspect. There's another zener (Z2) and a couple of ceramic caps (C4 & C10) nearby which I'd also like to replace.

Does anyone know of suitable replacements for the zener diodes and the ceramics?

A pic (not detached the board from the back plate yet):

Holy bulged capacitor!

Yes, those capacitors look toasted!

If you can see them, just read the numbers and letters on the parts that are dead. We could then point you to what you should get.

It would be nice if we could know what country you are in, so we could help find a parts supplier somewhat near you. (Reduce shipping costs...)

[fcda]

Re: M-audio AV30 speakers recap and repair

Thanks, I've added my country to my profile: Scotland. Usually get stuff from Farnell or RS.

The ceramics have 104 on them, so I think that's 0.10 uF.

I'm not sure if I'll be able to read anything off the burnt out diode. I'll try and de-solder it and see. Hoping SnowKitteh might have the details.

[Logistics]

Re: M-audio AV30 speakers recap and repair

Ceramics in audio path = bad idea. You can use polypropylene or polystyrene.

I admit that I didn't read carefully, but when did he mention the caps in question being in the signal path? (I'm in agreement with you, though.)

[maudioav30]

Re: M-audio AV30 speakers recap and repair

Hello,
Were you successful in your repair? I have the same issue, (C48 & C47 -25v 220uf), (z1 & z2 - ???), (r58 & r 57 -???) (c4 & c10 - 104? with a dot onto of the 0), and (two caps (can't determine pcb #'s) - 35v 4700uf). They all look bad so i figured i would replace them all. I have yet to determine exactly what z1, z2, r57, r58, c4 and c10 are? If i replace all of these will they most likely fail again after awhile?
thanks

[MarvinPoetry]

Re: M-audio AV30 speakers recap and repair

The zeners should 15v, I replaced with 1N5352 5W, Originals are 1W. I also replaced the 2 220uf caps, repaired the power connector and installed sockets for the 4558 and TL074 and replaced the ICs. None of this fixed the problem. I read that the 22uf cap, C13 that you can see in the above pic is the issue. I replaced both of those along the edge of the pcb with 10uf and it is working.

ymmv,
Marv

[spiff59]

Re: M-audio AV30 speakers recap and repair

I bought a dead pair of these for $5 at a Goodwill last week.
I cracked mine open and found a Rev 2.0 board where C47 and C48 are domed on top, have blown the plugs out the bottom, burned off their labels, vaporized any through-the-hole plating, and left a charred pit on the bottom of the PCB. One zener diode (which tests open in both directions) and the run around it is as toasted as were the caps. The second zener tests good but also shows signs of abuse.
There's plenty of real estate to scrape off some green lacquer and reinstall parts, but... It appears that the power supply section is flawed, and it going up in pyre is a common occurrence.
Would any amateur (or pro) designers know what's needed to make the basic power supply circuit in the attached schematic a little more bullet-proof?

I've no idea why the only difference in the PS between 2.0 and 3.0 would be changing the main filter caps from 4700mfd/25V to 3300mfd/35V. I suppose the reduced capacitance was just to end up with a 35V replacement cap of approximately the same physical size. But I'd think if they thought it necessary to bump C51 and C52 to 35V, they they'd have done the same for C47 and C48. Could I pitch the zeners and tack on little solid-state regulators?
Thank you

[stj]

Re: M-audio AV30 speakers recap and repair

i dont know how much current is flowing there,
but you could ditch the zeners and the 2w resistors and try a 7812 and a 7912 regulator pair.

[lexwalker]

Re: M-audio AV30 speakers recap and repair

Is that 14VacRMS from the main transformer? If it is then that would be roughly almost 20Vdc after rectification and smoothing. In such cases, I would recommend smoothing capacitors with 50Vdc rating. Also the bigger the capacitance the better for that smoothing capacitor (usually 4700uF and above). As for that 12V section, I have to agree with stj on using linear voltage regulators such as 7812 and 7912. Otherwise to reduce the stress on that zener diode, you may try putting a series of silicon diodes right before that 100 Ohm resistor to make the voltage drop a bit (each silicon diode usually have around 0.5V forward voltage drop)...

[mariushm]

Re: M-audio AV30 speakers recap and repair

If the connector says 14v AC @ 0.8A that means there's going to be about 20v after rectification, minus about 1v from the voltage drop on the diodes.

edit: The peak DC can be estimated using the formula Idc = 0.62 x I ac = 0.62 x 0.8A = ~ 0.5 A.

So 19v @ 0.5A... But keep in mind at very low currents the voltage drop on the rectifier diodes will be smaller, and the transformer may output 5-10% more AC voltage, so the DC voltage may reach a peak close to 25v, so it's safer to use 35v rated capacitors.

Let's assume there may be some voltage drop on the transformer at full 0.5A and say 17v DC minimum at any time after rectification.

With 0.5A at the output, normally I'd recommend 1117 regulators with 1-1.1v maximum dropout voltage, but these only support up to 15v at the input.
So you'd have to use 7812 and 7912 or LM317, LM337.. the classics, which have about 2v dropout voltage.

Therefore, if you really want +/-12v in the worst conditions, you want to have at least 14v at the inputs so then you can use the formula to determine capacitance.

C = Current / ( 2 x mains frequency x Vripple) = 0.5A / (2x60Hz x (17v - 14v) ) = 0.5 / 120x3 = 0.5 / 360 = 0.0013888[88] F = ~ 13888uF

So in theory, with minimum 17v DC after rectifier, with a 1500uF capacitor you'd have at any time 14v or more at the input of the regulator, even when 0.5A is pulled through the regulator. Going with higher capacitance, you will just get the minimum DC voltage higher, closer to 17-19v, which in turn will cause more power to be wasted in the regulator and therefore heat it up more, and you'd need a larger heatsink.
The amplifier won't use 12v @ 0.5A constantly, it will only use as much as needed, the average power draw will depend on the volume and how the music is.

But to be on the safe side, I'd still recommend going with a 2200uF capacitor or why not, even 2700-3300uF.

Even if you use a small capacitor, in the worst case scenario (when the volume is pushed very high and power consumption peaks), the input voltage will simply drop a bit below 14v, which means the regulators in turn will output a little bit below 12v. The amplifier chip is designed to work with a wide range of input voltages, so it won't mind a bit less than 12v for a few ms, but you may get a bit of distorted sound. Considering you won't use the speakers at maximum (at least I hope), this won't be a problem.


edit: I initially wrote this post with 0.8A DC current but I forgot to consider the losses in rectifier and smoothing capacitor, so the DC current is actually lower if you use just a rectifier and capacitor to smooth things out. So I rewrote this post with the correct peak DC current.

[stj]

Re: M-audio AV30 speakers recap and repair

what concerns me is current,
will the reg's need a heatsink?

[mariushm]

Re: M-audio AV30 speakers recap and repair

edit: corrected the post to assume 0.5A peak DC current instead of 0.8A.

Well, here's the datasheet :

On page 2, thermal Resistance, Junction-Air (TO-220) θja : 65C/W above ambient.

At 0.5A, the 1500-2200uF smoothing capacitor will give the regulator a voltage between 14v and 19v, on average let's say 16v.

At 16v in and 12v @ 0.5A out, the regulator will dissipate (16v-12v) x 0.5A = 2w so the regulator will be 25c (ambient) + 2 x 65C = 155 C.

On same page 2, you have the maximum operating temperature of 125C so yeah, you will need a heatsink.

Assuming 30C ambient (because the ambient temperature inside will get warm over time from transformer and other things) and assuming a safe 110C maximum regulator temperature, then you can figure out how big of a heatsink you need:

Tdelta = Tmax - Tambient = 110C - 30C = 80 C
Power dissipated = 2W

Thermal coefficient θ = Tdelta / Power = 80/2w = 40 C/w (which is less than 65C/w so heatsink is required)

Thermal Coefficient Heatsink θhs = θ - θ junction case - θ case-heatsink

θ junction case is in datasheet, 5C/w . θ case-heatsink is the resistance of the thermal paste you put between regulator and heatsink, usually it's about 0.2-0.5C/w)

So θhs = 40 - 5 - 0.5 = 34.5 C/W

So you need a heatsink with a rating of 34.5 C/w or smaller to keep the regulator under 110C when it works at the maximum 0.5A, with minimal airflow going over the heatsink. Ideally, you want to go as low as possible but that means taller or wider or longer fins.

Now you can go on Digikey to find such a TO-220 heatsink, you can simply filter by that θhs column (Thermal Resistance @ Natural in Digikey) and you find heatsinks such as this one:

17c/w : http://www.digikey.com/product-detai...S278-ND/373766

Here's a search result page, with TO-220 (and similar) heatsinks, sorted by price : http://goo.gl/30ivlu

You can look up how much space you have between the regulators (to see if the fins of the heatsink will fit), if you can fit that tall or wide regulator there...

Note that you don't HAVE to fit the regulators on the PCB, the length of the leads isn't really that important in this case, so you could solder some wires and then solder the wires to the regulators and glue the heatsink to the case or screw it to some other place near the power supply.

[stj]

Re: M-audio AV30 speakers recap and repair

i didnt need a lesson in 78-series regulators,
i meant i dont know how much current the circuit will draw through it!