Soundcraft Mixer Repaired
This musical mixer was brought to my workshop dead by a church Pastor who happens to be my co- worker when I was a chef at Sheraton hotel in my country. He also had retired and now a pastor.
I opened top cover which entails loosing so many nuts and knobs, about 80 pieces in all. Checked the power board with my tools and detected four resistors were burnt, mosfet and power ic defeated.
Changed all these with new ones and powered on, the power led lit but mixer didn’t show any sign of live.
Then checked all secondary components, all in good state, checked secondary out put voltages, out of three, only one was ok, others low. So what is the problem, so I decided to seek help from a techie friend, having check the psb , he said the smpt (switch mode power transformer) is defective at the secondary side but the primary winding passed my blue ring tester. So what do I do since I can’t get a replacement for the transformer!
He suggested he can modify the board with toroidal transformer! So he removed smpt transformer and connected primary wires of toroidal transformer to live side of bridge rectifier to get 220 voltage. Then connected the secondary wires of toroidal transformer to the anode sides of secondary diodes of psb, then the ground wire to ground of secondary side. Note: He didn’t remove any component from secondary of smps.
Then powered on, alas! power led lit and all other display LEDs lit, so I took the mixer to pastor church and connected it to sleeve amplifier and powered on the two appliances, connected microphone to mixer with shout of ‘praise God ‘ to mic, the loudspeakers boom out loud and clear.
This repair was done June 2022 and since then mixer has been working up to date. This is the finished repaired work.
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Note: You can read his previous article on LG Home Theater Repaired
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Tim Bianco
December 31, 2022 at 8:25 am
Praise God indeed! Nice work from you and your friend!
Parasuraman S
December 31, 2022 at 10:41 am
Vow! That is a very, very rare case! A good out of the box fix too! Many thanks for sharing!
Imoudu.O
December 31, 2022 at 8:19 pm
Tim
I always ask God in prayer for knowledge in repairs work(for knowledge comes from God) both spiritually and otherwise,and it has been working for me.Thanks for your comments.
Imoudu.O
December 31, 2022 at 8:23 pm
Mr P.S
Yes it's very rare."Out of no way,there must be a way" Thanks for your comments.
Albert van Bemmelen
December 31, 2022 at 8:37 pm
That sure was a very time consuming repair that hopefully now will last for a very long time. Replacing the defect transformer by upgrading it to a toroidal transformer was a very professional move!
Robert Spoon
December 31, 2022 at 11:38 pm
I repair these kind of mixers as well, most of the issues center around SMPS problems, I never thought to go analog which is a much cheaper fix [and probably more reliable] , thank you so much indeed! Praise God !
Waleed Rishmawi
January 1, 2023 at 1:28 am
Always praise to God for He is The One that gives wisdoms to repair stuff.
Gabor Zs.
January 1, 2023 at 10:40 pm
Mr. Imoudu,
the principle of toroid transformer replacement is good, it will probably last forever. Unfortunately, the implementation is flawed! It works but not the right one. Look at 50/60Hz vs. 50-100kHz. You need full wave rectification with appropriate diode and capacitor. For example 1N54xx or Graetz center tap transformer and 2*3300uF-4700uF. The coil on the output is redundant. The toroid draws high current when turned on, the fuse should take this into account. I write with good intentions to make your repair as perfect as possible.
Translated with www.DeepL.com/Translator (free version)
Imoudu.O
January 2, 2023 at 12:23 am
To
Albert,Robert,and Waleed.
Thanks all for your comments
Imoudu.O
January 2, 2023 at 11:11 pm
Mr Gaynor Zs,
Thanks very mush for ur observation and appreciated. In fact I have to investigate into this to expand my knowledge and experience.Thanks.
Imoudu.O
January 2, 2023 at 11:29 pm
Mr Gaynor,
You said I need "full wave rectification....." are you saying I should have connected the toroidal transformer to full wave rectification or I should have use the normal smps with full wave rectifier and not to have use toroidal tx the repair? I want to understand better.
AdamS
January 3, 2023 at 5:24 pm
As above, using a standard mains frequency transform in place of a proper high frequency transformer in an SMPS is not a good idea. The transformer will likely run much hotter due to the higher frequency. You may get away with it for a while as the new transformer is clearly much larger and so presumably has a higher power rating than the original, but it is not good practice.
Gabor Zs.
January 4, 2023 at 8:16 pm
The SMPS power supply could not be repaired, so the toroid transformer was installed. This is good, it works from the mains not from the SMPS. On the secondary side you should use full wave rectification.
Imoudu.O
January 5, 2023 at 4:09 am
Gabor,
OK,thanks
Yogesh Panchal
January 8, 2023 at 11:07 pm
Imoudu.O
Good attempt!