The right speaker of M-Audio Studiophile AV 40 (Active Audio 4 inch) speaker set that I have had started to go quite a while ago. In other words, only the left speaker (which houses most of the electronics in the set) was making a sound. My online research showed that a lot of people have been having problems with these speakers. Even the Amazon customer reviews for AV40 (#ad) were clear of how these speakers can be problematic. Considering that most people paid $150+ for these speakers, I thought it might be a good idea to fix my speakers and try to help others as well. Typical Problems with M-Audio AV40 speakers:
Type 1 Problem: Both speakers die after a while and do not turn on:The most likely cause besides the obvious (bad power cord, etc.): the power supply capacitors may have gone bad and would need to be replaced. You can physically diagnose this in most cases by opening the left speaker and looking at the internal power supply circuitry and looking for bodges in them. There are four capacitors for the power supply, and they are larger than the others toward the corner of the board near the 3-wire plastic connector header that comes from the transformer inside the box. You may also see some signs of overheating around the capacitors in the forms of a darkened circuit board, etc. The cause of this problem is that by design the two large blue power resistors that are standing off of the board next to the capacitors along with the Zener diodes that are next to them tend to pass quite a bit of current and are supposed to heat up. However, besides the ambient air-cooling in the enclosure, there isn't much to cool them down. The electrolytic capacitors lose significant of their useful life when operated in overheated conditions, which results in them breaking down in these speakers sooner than expected for a consumer electronic. You can read the value and voltage reading of the capacitor and replace them to fix the most power supply issues. Capacitors are about $1-$2 at RadioShack or even online at Amazon (see 220uf 25V capacitors on Amazon #ad)If the capacitors look to be fine, you may want to use a multi-meter, a DMM, or a voltmeter to check the output of the power supplies. The following are where you would find these outputs and the voltages that I measured (green markings). This can be caused most likely because of two reasons.
This is very unlikely, but if it occurs, it is because there is an issue with the crossover circuit in that speaker. Most likely, you can identify the problem by physical inspection of the circuit board in that speaker. The crossover circuit consists of two completely passive filters (one low pass and one high pass) as following. Type 4 Problem: There is only sound coming from one speaker (typically the left one):This is more tricky to diagnose. The first time I had this issue it got resolved by opening the board and doing a deep inspection, and magically, everything started to work again. I suspect that the cause is a lose internal connector/header contact. The second time that it occurred, I realized the faulty connector is one of the ones near the power supply. See the above photo.
The circuitry around the Output AMP is the following based on what I observed on the board. The numbers in the squares are the pin numbers on TDA 7265 amplifier: As a reference, the following crossover circuit is what I observed in these speakers. Each speaker has its own, and this circuitry is the only circuitry in the right speaker. Note that it is pretty passive, and it has a meager chance of failure due to its passive nature. The crossover circuit is two passive filters, the low pass filter is for WF, and the high pass is for TR, which results in the excellent dynamic range of these speakers. The circuitry for the left speaker is integrated into the mainboard, while the right speaker has its circuitry in it. Power Amp - TDA7265 , Datasheet: http://datasheet.octopart.com/TDA7265-STMicroelectronics-datasheet-14136201.pdf Input Amp - 4558, Datasheet: http://www.ti.com/lit/ds/symlink/rc4558.pdf OpAmp - TL074, Datasheet: http://www.ti.com/lit/ds/symlink/tl074.pdf Block diagram for AV40, see appendix B of the user guide: https://cvp.com/pdf/av40_user_guide.pdf AV30 schematics - note this is somewhat different than AV40, but there are also some common parts: http://music-electronics-forum.com/t33027/#post302749 http://blog.melissadunphy.com/2013/12/fixing-buzz-in-my-m-audio-av-40-speakers.html Was not applicable since my AV40 did not have the fuses that the user mentioned, but interesting: http://forum.allaboutcircuits.com/threads/advice-regarding-transformer-for-powered-speakers-studophile-av40.56757/ |
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