Mackie SRM450V2 solutions

[verano]

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

[verano]

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....

[kaise419]

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

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....

[guitardad]

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.

[romaci2005]

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

[guitardad]

I was on vacation, sorry for the late reply.

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

[romaci2005]

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

[romaci2005]

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?

[Jazz P Bass]

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.

[romaci2005]

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

[Edzone]

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.

[Enzo]

Sorry, not a mistake, it is as designed for reasons I explain in your other post.

[Be79n]

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.

[nickb]

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?

[Be79n]

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.