Rescue of a Sound Craft Mixer EPM8
This Mixer was brought to me in dead condition by my friend. This was being used by his friend in US, and went dead with a sound. Since getting it serviced is a very costly affair there, it was brought to India and given to my friend to find out whether it can be rescued.
Before dismantling, I noted down the colour of the knobs and its position in each row. Opening this unit was a laborious task, as I had to remove not only 38 screws from top, sides and bottom, but also remove 26 nuts and 90 knobs!
Cover removed
Rear Cover
Since the power supply unit is at the bottom, I had to remove 12 screws of the PCB and other screws holding the SMPS (The set has totally around 60 screws). (Unfortunately I forgot to take snaps of the board before fitting it back). The SMPS was using UC3842 IC and an N Channel mosfet. Fuse was blown indicating shorted components. Found one 100V 5 W Zener diode (PKIN5378B) connected between the primary winding of the SMPS transformer shorted! A few other components were also charred.
The circuit board
So, I removed the IC and all the components on the primary side, marking the symbol on the PCB and noting down the values in a sheet of paper, with reference to its number printed on the PCB. Checked the SMPS transformer using Blue Ring Tester bought from Jestine Yong, and ensured that there was no problem in the secondary side. (Thanks to him again, for his wonderful book on SMPS repair). Connected a universal smps switching module to the primary and got rated voltages of 48V and dual 15V. So, the SMPS transformer as well as the secondary circuit were ok. ESR of caps were also ok. Replaced the IC, mosfet, diodes except the 100V Zener, as it was not available anywhere here.
Put back the other components that were found ok in thorough checking. Since 100V zener was not available, which was provided as an over voltage protector, I tried using four numbers 25V 1W zener in series. But that also got shorted. So decided to forgo this! Connected a bulb across the fuse and switched on, got the rated output voltages. So, SMPS was ok! Here are the components replaced on SMPS:
Turned my attention to the board and found one op amp IC 5532 charred, PCB and smd components burnt beyond recognition. Downloaded the service manual from net. Since this has two channels, left and right, I compared the values with the other. Removed the charred ics and components, thoroughly cleaned the PCB. Scraped the black marks. Then replaced the SMD IC along with the 7 SMD components. Since the positive and negative supply tracks going to pin 4 and 8 were burnt on this double sided PCB, I wired it directly from the other IC. See picture below:
Totally 8 components including the IC were replaced, 4 SMD resistors, 3 SMD Capacitors and SMD Op Amp IC 5532
Checked and found the set got back its life! Checked all the inputs feeding songs from a self made USB player, by connecting two RC jacks to stereo jack and used the left and right channel fader and found it to be in perfect working condition. Put back the PCB and all the screws, nuts and knobs.
A job accomplished well!
This article was prepared for you by Parasuraman Subramanian from India. He is 65 years old and has more than 30 years’ experience in handling antiques equipment Valve Radio, Amps, Reel Tape Recorders and currently studying latest techs classes conduct by Kerala State Electronics Technicians’ Association. He was a BBA graduate, retired as MD of a USA company and presently working as Consultant Manager, Purchase & IT, in Irinjalakuda Cooperative Hospital.
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https://www.jestineyong.com/lg-lcd-tv-repaired/
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30 Comments
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Bernie Scott
April 3, 2015 at 9:42 pm
Great job....I can relate to the time involved here for this type of repair....If in North America the repair would have cost more than the original price...or it would have been taken in for repair and slowly worked on while more revenue generating equipment was being repaired....I too repair this type of equipment and have had 24 channel boards that are not individual channel strips...just one complete board and every single screw, nut and washer has to be removed....very time consuming......Hats off to you sir
Randy
April 4, 2015 at 11:12 pm
I have people at work and elsewhere who ask me how to fix electronics all the time, they want to do the repairs (some fairly complex) themselves so they won't have to pay me to do it. These same people have never done anything for me, not even buy me a cup of coffee. Do you think you should give your intellectual property away? You earned it thru hard work and school, and yet most people think you should give it away, are you that little of value?
Bill Eitner
April 5, 2015 at 10:40 am
I work for a non-profit part of whose mission is technician-level computer service training. I'm the manager, instructor and senior tech. Believe me, few people have what it takes to do component-level electronics repair without a ridiculous amount of guidance. In other words, when it comes to the vast majority of people, you can tell them what to do, they can read about what to do, and they can watch YouTube videos about what to do and still not be able to do it because they don't have the background, dexterity, equipment, etc. It takes more than a desire. Sure, everyone wants to do whatever will save them some money. But information in and of itself isn't nearly enough. No one should feel threatened by simply sharing techniques and case histories. I spend my days doing everything I possibly can in an effort to produce competent techs. Over the years
disappointingly few have actually made the grade.
Yogesh Panchal
April 3, 2015 at 9:50 pm
Sir, It looks tedious and challenging job. sir one question
How did you find value of SMD Capacitors? and how did you arranged SMD components in India ?
Thanks for sharing your experience .
Parasuraman S
April 3, 2015 at 11:44 pm
I had mentioned that I downloaded the service manual from net. I looked for the values by referring to the circuit diagram and matching it with the component number printed on the board on the other channel which was clean and working. SMD capacitor has colours, guidance of which is, if I remember well, Jestine Yong has covered in one of his books. It is available even in net. I bought the SMD components in Sadar Patrappa Road, Bangalore through my son, who is working at Bangalore.
Shiharan Choudhury
April 3, 2015 at 9:59 pm
Good work, but it's not always that if the fuse is blown and the transistor is out, the PWM IC will also be out.
S Ramachandran
April 3, 2015 at 10:59 pm
very good job done Mr parasuraman, very informative one
Bradley
April 3, 2015 at 11:35 pm
Very tedious job and required great patience. Thanks for sharing
this great repair job.
Luciano Khware
April 4, 2015 at 2:23 am
Well Done Sir, thanks for sharing your experience. Keep it up!!!
Anthony
April 4, 2015 at 3:29 am
Very tedious work but you are rewarded with the great satisfaction of the mixer being brought back to life ! Congratulations to you Sir on your efforts. Thanks for sharing your repair story.
mustabz
May 22, 2015 at 4:30 pm
you deserve a hand full of loud claps and pats on your shoulder. great job done
moshe
April 4, 2015 at 5:33 am
very very nice job!!
thanks for sharing
Mark
April 4, 2015 at 10:37 am
Well done. Sometimes it is the disassembly/reassembly that takes all the repair time. The actual repair of the unit may only be a short time. Yes, patience is essential!
Thanks for your article
Mark
Bill Eitner
April 4, 2015 at 11:12 am
Re: Universal SMPS Switching Module
Where can I find more information?
Sounds like a useful tool.
Dijitalmemo
April 4, 2015 at 1:58 pm
Thanks for sharing. Great job.
Tito Kanshulu
April 4, 2015 at 3:06 pm
Very good job sir,and well explained.
Imraz
April 4, 2015 at 3:58 pm
Good Job Sir
It seems like you are a pioneer in Audio Repairs. I also work with amplifiers, mixers, lights, poweramps speakers etc. and has repaired some renown brands here in fiji to name a few like SoundKing, Soundcraft, Ahuja, Jarguar, Alpha, Phonics, Peavey, Carvin, Casio, Aston, Yamaha... I have not worked with Valve amplifiers much but would like to know more.
Sir I will be oblighed if I can have your email to correspond in need.
Thanks and keep us young technicians update
sam montero
April 4, 2015 at 7:03 pm
A great job well done and rewarded with a good feeling for being persistent in finding the bad parts and its replacement.
Again its just great job well done.
Sam
Andre Gopee
April 5, 2015 at 1:32 am
Job well done. Keep up the good work.
artisan
April 5, 2015 at 6:13 am
Excellent repair ! I can relate the tedious nature of the repair , a mixture of time and cost .
This is true skill !!! When people realize the lengths you have to go to I order to fix a dead unit, they will think twice about buying certain brands . Also they should not quibble when it comes time to pay for work done .
alex
April 5, 2015 at 11:32 am
very interesting work sir! thanks for sharing. cheers!
Luis Estrada
April 6, 2015 at 3:38 am
I've never worked on a sound mixer; however, your handiwork is the sign of a genius! Thanks for sharing your knowledge and illuminating us.
udaysinh shinde
April 6, 2015 at 4:44 pm
sir,
i liked your this experience. thanks for your valuable information
Humberto
April 6, 2015 at 11:03 pm
Great job Parasuraman Subramanian, your patiente was the key.
shahid ahmad
April 9, 2015 at 8:49 pm
very good.
reza
April 9, 2015 at 11:00 pm
hello mr Parasuraman Subramanian
thank u
your article is very good and usefull.
by
dicksy
April 11, 2015 at 5:05 pm
what a nice and clean work mr Subramanian.welldon and thanx
dicksy
Ali Darwaish
April 16, 2015 at 1:14 am
Well done could you please share with us the service manual of this mixer.
Regards,
Ben Damoiseaux
January 21, 2019 at 11:29 pm
Marvelous job !
Just found our epm8 smoked.
New one cost 190 $...
Unfortunately I will not go your narrow winding path to get it alive.
Great job Sir.
Ed
April 4, 2023 at 8:29 pm
I want to clear the dust from my Sound craft mixed its the notepad 124 8 channel
From Your website I was suprised to see nuts to which parts would these be connected inside the mixed some form if Bolt of course and why
Also Presumably the screws won't unscrew easy since they are done with a machine is that right
Thanks