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Thread: Mackie SRM450V2 solutions

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    Mackie SRM450V2 solutions

    Here are some fixes for these:

    Problem with HF or no HF output- replace U31 TDA 7294

    No audio at all- check resistors R243,248, 288 (upper board by SMPS).

    Audio not as loud as it should be, Audio weak at mic level or not much change in level from 4db to mic position/+40db max-
    Open R22 (smd resistor 10 ohms)

    Audio cuts out- check for a glob of yellow brown glue (similar to what mitsubishi used to use) near R3, R7, R8, R11, C6, C7 and U3. Cable from the XLR board is often glued and that glue covers a few smd resistors and small smd caps. The glue tends to break off (vibration/transport) taking one or more smd parts with them. This one will often make you decide to replace the entire board assy because you threw it across the room.

    No LF drive at all- replace U28, Q11, Q12, D19 adn D23. Also check R156 and R157 for opens.

    Intermittently won't turn on or won't power completely or has hiss sound then dies when powering up-
    C189- 192 may be dry/open. Check those with an ESR meter if you have one, or just replace them.
    C189,190- 680uf@200v ; C191,192- 220uf@200v

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    Senior Member mozwell's Avatar
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    for those that need the service manual....
    Attached Files Attached Files

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    Supporting Member Jazz P Bass's Avatar
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    Quote Originally Posted by guitardad View Post
    Audio cuts out- check for a glob of yellow brown glue (similar to what mitsubishi used to use) near R3, R7, R8, R11, C6, C7 and U3. Cable from the XLR board is often glued and that glue covers a few smd resistors and small smd caps. The glue tends to break off (vibration/transport) taking one or more smd parts with them. This one will often make you decide to replace the entire board assy because you threw it across the room.
    Been there.
    Done that.
    (threw the board across the room)

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    I'm trying to repair this speaker. When i got it there was a hole burned in to the UC3842 on the board. Replaced this on a socket. Also the 12N60C was broken, Replaced R332, R288, R245, R243, both 18v zener diodes, D33, 2x 680uf 200v caps ( c189, c190), the LM339, and tomorrow i will replace the 220uf 200v caps (c191, c192). When i try to power up the board that is connected trough a 60watt light bulb to the mains. R245, R288 heats up within 10 seconds. Anybody a clue what to look for ?

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    Supporting Member Jazz P Bass's Avatar
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    What page are you on?

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    Page 6 the powersupply

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    Supporting Member Jazz P Bass's Avatar
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    Thankyou.

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    I spend hours troubleshooting this thing... Maybe a trow it in the room would help

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    Quote Originally Posted by verano View Post
    I'm trying to repair this speaker. When i got it there was a hole burned in to the UC3842 on the board. Replaced this on a socket. Also the 12N60C was broken, Replaced R332, R288, R245, R243, both 18v zener diodes, D33, 2x 680uf 200v caps ( c189, c190), the LM339, and tomorrow i will replace the 220uf 200v caps (c191, c192). When i try to power up the board that is connected trough a 60watt light bulb to the mains. R245, R288 heats up within 10 seconds. Anybody a clue what to look for ?
    I think that the power supply is designed incorrectly; both resistors heat up "by design". The first one dissipates 1.3W (and is rated 1W only) and the second dissipates 2.5W (and it's rated 3W only). Both resistors should be replaced with higher rating (the first one 3W, and the second one 5W). The best way to troubleshoot the power supply is to understand how it works and verify what is not working as expected. You should understand which voltages supply which part of the circuit and verify the voltages. I assume that you have 380V (since the resistors heat up quickly). But did you verify 18V rails (there are two of them: 18V and VDD)? Do you have 25V rail? Did you verify that the output diodes are not shorted? If you replaces so many (possibly burnt) components, I assume that you checked that Q7 and Q10 transistors are not shorted, did you?
    Did you try to measure the voltages on the output ? Maybe it's already fixed and you only need to replace the resistors.
    I also wonder why you replaced all the capacitors - what was wrong with them?

    Mark

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    Supporting Member Jazz P Bass's Avatar
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    It sounds like something downwind on the 18 volt rail is pulling current.
    Is there a way to disconnect the +18 volt rail?

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    Thanks for the reply's. I just powered up the amp, and the 12N60C just died. When it shorted out, the lightbulb in serial with the mains goes on. Means i have a shortage in the main supply.
    I had a MM measuring the voltage on the D63 18v zener diode. It came up from 10 to 14 volts and then de 12n60c goes bad. Don't have a spare one to replace it. So i have to order it again. I replaced the 680uf caps because one of them did not match the specs anymore. Someone adviced me to change both. If i disconnect the 18v rail the smps has no voltage to power up ? Q10 and Q7 are replaced and not shorted, even after the 12N60C goes bad...

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    Question, why did they connect the VDD (5) coming from c241 to the emitter of Q28 ?

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    Why does it worry you? I think that this is typical solution used in many SMPS. A circuit is supplied from two sources. One may be more important during startup of the power supply and the other when the supply has already started. And the key here is to understand that it's not VDD(5) supplying Q28 but two voltage sources are suplying SG3525.

    Mark

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    I just wondered and wanted to find out what it did, not worried at all I replaced the 12N60c again. The mains short is gone now... Did some measurements. When is measure on both sides of R288 the voltage starts at 190, and keeps climbing to 260 volts slowly... Meanwhile the resistors get hot around the MJE13003... Can't find out why...

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    Quote Originally Posted by verano View Post
    Meanwhile the resistors get hot around the MJE13003... Can't find out why...
    In post #9 I wrote you why the resistors get hot - have you read it? They are under-rated. Which exactly resistor gets hot? Measure what is the voltage drop on it.

    Mark

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    Yes i have read it, but the psu/amp is not starting up anyway... i will do the measurement asap and keep you posted

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    Measured the voltage today, its from 302 volts dc to 15 volts dc... I got a second working SRM 452 V2 amp now. I measured 382 volts dc on the working one....

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    Mackie SRM450v2

    Hi, this is my first post and I hope someone can help me, the case is that I have a Mackie SRM450v2 that I don't use to much but after a few weeks without using it, when I powers it up the blue LED did not turn on and the power led neither, just the thermal and peak LEDs, is there anything I can check or change to fix it? I have little electronic knowledge but I can do it if anyone can help me, is there any specific elements that I can check on the board? can send me comments by here or email me at kaise419@aol.com, I will appreciate any help, thanks



    Quote Originally Posted by verano View Post
    Measured the voltage today, its from 302 volts dc to 15 volts dc... I got a second working SRM 452 V2 amp now. I measured 382 volts dc on the working one....

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    Check those resistors at the top of the circuit board. Also check the two low voltage regulator IC's just behind them. They often vibrate and crack the leads right at the board contact. That opens the circuit. Look for obvious things. Overheated components, broken leads, and so on first. Again these units vibrate and that causes parts to become fractured at board contacts. You really have to look hard. If all that is good, get out the DMM and start checking voltages. Especially check the low voltage supplies.

    I have not changed any of the large caps in these units, but I have in the Iron versions (no switching supply) of the 450V1. I dont use a standard cap checker either. ESR meters for me are best for checking electrolytics.

    Check the outputs as well as the HF driver output IC. Look to see if that IC is cracked or burned (funny smell). If it is cracked, burned or shorted, it will load the power supply down.

    This is a very complex amp and power supply. Be sure you have the right equipment before digging in.

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    I have a SRM450v2 found open track between drain of Q7 and VDC [5]
    I replaced defective components R288, R245, R243, D37 (18V), D62 (18V), Q1 (S8550), U36 (UC3842), C241, C242, D39,

    D37, D7, D62, LM339, C191, C192

    I checked all the diodes and MOSFET connecting them to the module tests are well Q21, Q7, Q10,

    Q12, Q11


    18V power intemittently in [5] measured 16V and off, C191 and C192 (220uF/200V) are warm


    what else I can check, any suggestions?

    regards

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    I was on vacation, sorry for the late reply.

    What are all your rail voltages and LV power supply voltages reading?

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    Thanks for responding.
    VDC [5] = 300V
    18V [5] = 17V
    VDD [5] = 17V
    I dismounted Q21, Q7, Q10 to isolate the circuit
    UC3842 intermittent ranges approximately 60kHz

    U35 SG3525 not oscillates with an external source of 5 volts on pins 12 and 15
    I will replace it

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    I replaced the SG3525, now oscillates back but still continues flashing the UC3842

    takes a long time to connect to appear in UC3842 18V

    the VGS voltage at the MOSFET connected to the integrated circuit SG3525 is low 0.5 Vpp

    the fault is in the primary of smps

    alguna sugerencia?

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  24. #24
    Supporting Member Jazz P Bass's Avatar
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    Have you had any success with the repair?

    I had one come through where the UC3842 & the LM339 where blown in half.

    The result was Q21 mosfet was bad & that made R 233 (0.1 ohm) sense resistor fail open.

    Additionally D62 (18 volt zener) was shorted, Q13 was shorted C to E, D3 was open, & R173 was damaged such that it read 7K (should be 3.3K)

    I also replaced the main controller, U35, to be on the safe side.

    I noticed that an awful lot of the through hole via pads did not have any solder in them at all, so I hit them with the iron & solder.

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    Last edited by Jazz P Bass; 12-24-2013 at 04:09 PM. Reason: spelling

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    I have not been able to repair, is intervened in another workshop, had missing parts and damaged

    I replace defective components Q28, D37, R245, R243, D39, C242, C191, C192, D62, UC3842, Q21, Q13, Q1, Q8, SG3525, C163, C173, R293, D63, R241 (Q7 and Q 10 are well ).

    UC3842 still intermittent enable shutdown.

    VDC [5] = 320V
    VDD [5] = 17V
    18V [5] = 17V

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    Has paid attention someone to the link that goes from +12VDC supply (does not measure +12V but -63.7VDC) GND pin/tab of the U34 (7812 IC) to the -75V DC supply? are this correct???? because on the minus side of the C208 and anode of D42 measure -61.3VDC and at the output of IC U34 measure -63.7VDC, so where the 12Volts measures??? Are not this link (which I consider it a big mistake) the big problem of almost all of this V2 problems presented ????
    THANKS and Very Good Day!!!!Edu.

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    Lifetime Member Enzo's Avatar
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    Sorry, not a mistake, it is as designed for reasons I explain in your other post.

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    Quote Originally Posted by guitardad View Post
    Here are some fixes for these:

    No audio at all- check resistors R243,248, 288 (upper board by SMPS).
    I have a 450V2 that powers on fine but no audio at all, How do I test these please?. I have found them on the board and do have a multi meter, if they was failed and I was to try and replace all three would the audio start working again or is it more complex then that?. Thanks in advanced, I'm just real tight for money at the moment and been quoted 170 for the repair.

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by Be79n View Post
    I have a 450V2 that powers on fine but no audio at all, How do I test these please?. I have found them on the board and do have a multi meter, if they was failed and I was to try and replace all three would the audio start working again or is it more complex then that?. Thanks in advanced, I'm just real tight for money at the moment and been quoted 170 for the repair.
    I hate to pour water on the idea but these are not boards that are suitable for a novice to work on. Where are you located?

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    Quote Originally Posted by nickb View Post
    I hate to pour water on the idea but these are not boards that are suitable for a novice to work on. Where are you located?
    Thanks being honest, I'm in Essex. Happy to post for repair. A placed has offered to look at it for 80 hopefully with a fix, about another 30 postage.

    Any advice would be good.

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  31. #31
    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by Be79n View Post
    Thanks being honest, I'm in Essex. Happy to post for repair. A placed has offered to look at it for 80 hopefully with a fix, about another 30 postage.

    Any advice would be good.
    You need to put your meter on the resistance range and then carefully put your probes across the ends. There are multiple problems - the components are tiny, easily damaged and the probes are big. You will be measuring with the components in circuit and that can change the readings. If it is these resistors that are faulty you need the tools and skill to change them. There is a good chance that it's something else. Look for damaged or burnt parts. Re-seat any connectors.

    Essex, huh? A heavily populated area. There has to be someone within driving distance from you that can take to look. That will save you on the shipping.

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    See I' not sure I would feel comfortable with that, I'm a freelance sound & light service technician. I look after hotels, resorts and venues etc so more then happy to service/clean gear but don't have the confidence on circuit board soldering that is so small on a board I'm not used too. If anyone is local and able to fix it I'm happy to pay a decent rate. Thanks for your help Nickb.

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    Quote Originally Posted by Be79n View Post
    See I' not sure I would feel comfortable with that, I'm a freelance sound & light service technician. I look after hotels, resorts and venues etc so more then happy to service/clean gear but don't have the confidence on circuit board soldering that is so small on a board I'm not used too. If anyone is local and able to fix it I'm happy to pay a decent rate. Thanks for your help Nickb.
    You can check the resistors in circuit. Leave unit off for 20-30 min. Caps will discharge on their own. Grab a DMM and see what readings you get on the resistors. Chances are they overheated and are out of tolerance. Replacing them with same value components is another option. This is fairly a common problem of the 450V2's

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    Thanks but I ended off sending it for repair.

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    Quote Originally Posted by guitardad View Post
    Here are some fixes for these:

    Problem with HF or no HF output- replace U31 TDA 7294

    No audio at all- check resistors R243,248, 288 (upper board by SMPS).

    Audio not as loud as it should be, Audio weak at mic level or not much change in level from 4db to mic position/+40db max-
    Open R22 (smd resistor 10 ohms)

    Audio cuts out- check for a glob of yellow brown glue (similar to what mitsubishi used to use) near R3, R7, R8, R11, C6, C7 and U3. Cable from the XLR board is often glued and that glue covers a few smd resistors and small smd caps. The glue tends to break off (vibration/transport) taking one or more smd parts with them. This one will often make you decide to replace the entire board assy because you threw it across the room.

    No LF drive at all- replace U28, Q11, Q12, D19 adn D23. Also check R156 and R157 for opens.

    Intermittently won't turn on or won't power completely or has hiss sound then dies when powering up-
    C189- 192 may be dry/open. Check those with an ESR meter if you have one, or just replace them.
    C189,190- 680uf@200v ; C191,192- 220uf@200v
    I have the issue where the audio is not as loud as it should be. Can you throw a little more light on this.
    I am ok with soldering and can easily purchase the resistor but is it a straight forward job?
    Thanks

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