Re: Repairing Alesis M1 Active mk2 Monitor Speakers
No voltage is being issued from the input channel on either unit.
Skeeter
Member
Last Activity: 09-04-2022, 01:35 PM
Joined: 06-30-2022
Location: Forest, VA
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Per Hansson:
Well, I have ruined another sound card/interface. I just ruined Bluetooth interface #3 (that's in addition to 2 sound cards). So, after all this work, I am sorry to say I am discouraged and I give up. This bothers be terribly, but I don't want to risk causing more sound card/interfaces to be broken. I think that if I do anything more with these speakers, I will learn how to make them Passive. The speakers are in pristine condition, like they were when they came out of the box brand new. Any advice...Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Thank you.Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Without the Behringer:
C8 voltage measures 17.5VDC.
Purple to Green = 19VDC
With the Logitech bluetooth adapter:
C8 voltage measures 17.5VDC
Purple to Green = 19VDC...Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
I have also found the following:
The Behringer line out measures 24K ohms. (my Alesis monitors blue light blinks and sound does not work with this unit, even though it works with other speakers)
The Logitech bluetooth device measures 15K ohms. (my Alesis monitors work with this unit)
My laptop headphones out measures 7K ohms. (my Alesis monitors work with this unit)Last edited by Skeeter; 08-16-2022, 06:38 AM.Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Yes, I am disappointed that I am having this issue! If I need to replace the Behringer unit for another, I can understand, since I did not spend too much $ on it. However, I just don't want to guess and buy another sound card only to find it will not work, either!
I will measure both of these. Can you please tell me the voltage that should occur across C8 when operating properly (and/or improperly)?
Just to clarify: you want me to measure Green (neg) to Purple (pos)?
While connected to the Behringer...Last edited by Skeeter; 08-15-2022, 06:13 PM.Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Yes, the Behringer USB sound card works with other speakers.
Yes, the same thing happens to both Alesis monitors. I have not allowed the connection to be on for more than 5 seconds, because I do not want to damage the Alesis M1 monitors. The blue LED light blinks, so I expect it is a warning.
Thank you....Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
After doing all the repairs, I have a new problem:
I have successfully connected my computer to both of my Alesis M1 Active Mk1 monitors via a bluetooth adapter with RCA outputs. I run the RCA cable to the speakers, and have high quality RCA to unbalanced 1/4" plug adapters. Everything works great! However, when I connect exactly the same to my computer with a Behringer UCA222 USB audio interface, the blue led light on the front of the monitors blinks, the same way they did before I replaced C8. When I revert...Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Understood.
Very good. Thank you.
I will order them and install. Thx
One of Khron's photos showed the C8 with long leads, which is exactly as I have done. So, I will start by just bending away from R4, just the same, and skip the cooling fan idea.
Will do!
Thank you very much! This has been quite the adventure for me!
...
Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Attached is my parts list, so far, not including any cooling additions....Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Wow! You continue to be a tremendous help to me! Thank you.
R24 does measure 15K ohms out of circuit.
If C35 has failed, wouldn't that keep the unit from functioning, just like when C8 failed?
Will do!
I have the braid, but will get the flux, too, to help.
Good advice! I will wait to install the new parts before using the studio monitors.
I replaced C8 & C35 (not C38) on the non-functioning board. I purchased...Last edited by Per Hansson; 08-10-2022, 10:36 AM.Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Since I know you are the pro, what Resistor do you recommend from the following? (pics attached)
R15
R24 (Only 1 kind in stock with the parameters offered at DigiKey)
Thank you for ALL your help!!
Skeeter
UPDATE!! I swapped the 22 ohm resistor with the old .22 ohm resistor (which is in terrible shape), and IT WORKS!! Basically, the .22 ohm resistor is barely holding a connection, so I still need to order a new one, and I will still replace the 15K resistor,...Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
I have discovered the following resistor issues on the non-working power supply:
R24 is supposed to be 15K ohms, but it only measures 3K in circuit
R15 is supposed to be .22 ohms, but it measures 22 in circuit - this is a resistor that I replaced, and it appears I replaced it incorrectly with a 22 ohm resistor. I have the old one, and it measures .22, but it is in pretty bad shape, including the post is broken off at the body of the resistor, so I don't know if I can get a good reattachment.
...Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
This was my precisely my thought yesterday, that everything seems to be working as it is supposed to. So, yesterday, I reassembled everything, and turned on the units to see if the blinking led still persisted. And, yes, still blinking, and no sound from the non-functioning unit. (previously, I had also swapped power supply PCB from the 'good' monitor into the nonfunctioning monitor, and the nonfunctioning monitor indeed did function - so, I am convinced it is an issued located on the power supply board).
When you...Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
I did an ohms test UC3844N of the working power supply and the nonworking power supply, using Pin #5 GND for Neg probe, and testing each pin. Below are the results.
[B]
Working Power Supply[/B]
Pin 5 to 7 = 28 Ohms
Pin 5 to 1 = 37 Ohms
Pin 5 to 2 = 46 Ohms
Pin 5 to 3 = 47.5 Ohms
Pin 5 to 4 = 35 Ohms
Pin 5 to 6 = 31 Ohms
Pin 5 to 8 = 35 Ohms
[B]Non-Working Power Supply[/B]
Pin 5 to 7 = 28 Ohms
Pin 5 to 1 = 37 Ohms
Pin 5 to 2 = 46 Ohms...Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
UC3844N - is there a test to determine if it is bad?
Q5: yes, PNP (I think I mistyped the kind), and forward = open; reverse = 30 ohms.
Q1 & Q2. I have a question...if I only connect a 12V positive lead to the gate, how is any current transmitted? I am calling the 12V application "Test A" below, and the non- 12V application "Test B." Nonetheless, I found the following:
Q1: Test A (with +12V to gate). Without the 12V = 18 ohms; With 12V = 18 ohms - no change (but, don't...Last edited by Skeeter; 08-08-2022, 10:12 AM.Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
I tested the 'good' power supply, and found that each of the transistor measurements were exactly the same as the problem power supply, with the exception of Q7. On the 'good' power supply, Q7 measured open circuit in the forward test for PNP, and 30 ohms on the reverse (on the problem power supply, Q7 was 300 ohms forward, and open reversed).
I will get to work on the other recommendations soon.
Thank you again.
About 30 minutes later, and I have the rest of the results:...Last edited by Skeeter; 08-08-2022, 07:56 AM.Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Wow! I am learning a lot from you! I followed your instructions exactly, and here are the results:
1. Q3 NPN diagram. (base with Pos lead and Emitter with Neg lead). Measurement = 30 ohms. Reversed (base with Neg lead and Emitter with Pos lead) = 30 ohms again. I did this and each one below in the same order as you described.
2. Q6 NPN diagram. Forward = 150 ohms. Reversed = 30 ohms.
3. Q4 PNP diagram. (base with Neg lead and Emitter with Pos lead). Measurement = 30 ohms. Reversed (base with...Last edited by Skeeter; 08-07-2022, 07:02 PM.Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Thank you again.
I inspected the board carefully. The darkened areas are still the same as has always been, and I checked all tracers for good connections again.
Q1 Q2, Q3, Q4, and Q5 all appear excellent - nothing to suggest a problem.
I kept the board disconnected from the amp board, and left it running for more than an hour. I could detect a slight warmth from the board, but nothing hot. It could have been the C6 and C7 just slightly warm to the touch, but certainly not even close to being considered...Last edited by Skeeter; 08-07-2022, 03:13 PM.Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
I measured the resistance of D5 in both directions. Neg to Pos is open, while Pos to Neg shows 28 ohms resistance. I compared this to the "Good" power supply D5 on PCB, and the pattern is exactly the same.
Also, just to see the result, I measured the resistance of D1, D2, D3, and D4. Each one is open Neg to Pos, while each one shows 24 ohms Pos to Neg.
I also ran the light bulb test you recommended. I have a small 12V power supply, and used a 12V bulb with test leads and my probes to reach the...Last edited by Skeeter; 08-06-2022, 01:41 PM.Leave a comment:
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