RCF Active Speaker System Repaired. Model: ART 300A
An audio technician guy brought this RCF active speaker system to my shop and told me that he can turn the speaker on but he cannot hear any sound coming out of it. I plugged power in and I could see the power button coming on. I should be hearing some kind of noise when the speaker comes on but I did not. Instead I could smell something burning inside. Quickly I turned it off and took it apart.
I had to take a lot of screws off to open the back cover but finally I opened it. I took a deep look inside and the thing that caught my eyes was the burnt resistor on the side of the audio board. It smelled bad too indication there is a serious problem inside. It was a fuse resistor that it turning dark and smelling bad. I also found two open fuses on the same line of the resistor.
I wanted to understand what kind of circuit I am dealing with so I replaced the two fuses and turned the power on and I right away I could see this fuse resister turning to red. It was really getting hot which indicate some kind of shorts in the circuit. Turned it off and started to check the component in the circuit.
I started tracing the lines starting from the main fuse and got all the way to the fuse resistor and all checked ok. My focus was to check something around that resistor to see if something is shorted out. I could not find any bad components there. I must have missed something on that line so I went checking the same line backward and to my surprise, I saw a 12 volts zener diode DZX85C that is shorted out. It was located near the fuse that was open. This shorted zener was making some kind of loop in that circuit causing the fuse resister to heat up and the main capacitor was not discharging at all.
The moment I took the zener out and replaced it and also replaced the fuse resistor with a new one, the speaker system came back to life and I could hear nice music coming out of the speaker.
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.
Note: If you have any interesting repair article that you want to share to others please do contact me
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chantrea
May 22, 2013 at 12:26 pm
Thank for your good article Mr Jestine Yong .I enjoy reading.
Jestine Yong
May 22, 2013 at 3:32 pm
Hi Chantrea,
You are welcome!
Jestine
Jestine Yong
May 23, 2013 at 5:27 pm
Hi Waleed,
There is a comment about your article. It was contributed by Shaikh Ali from Canada:
"I have a comment on the article by Waleed on speaker system repair. During testing, many circuits can be powered up in series with a 75 Watt lamp rated at the line voltage. The lamp absorbs most of the line voltage if there is a short circuit as described, and prevents further damage. If the device is working properly, the lamp may glow at reduced brightness.
For low power devices one can use a 5 or 25 Watt lamp and for high power devices one can use a 100 or 150 Watt lamp. One can parallel lamps if the higher Wattage lamp isn't available.
For convenience, one may construct a simple circuit using a lamp socket connected to a line cord and leads terminating in alligator clips to attach to the power cord of the device. Lamps of different Wattages can then be easily swapped in and out.
Call me if you ever venture out to Canada."
Shaikh Ali
Leung Wing Kai
May 27, 2013 at 3:51 pm
Dear Shaikh Ali ,
Hi, I would like to ask where you live in Canda.I'd stayed in Calgary by 1990 and worked as a technician in troubleshooting those monitor & power supplies etc. At that time I'd to trace the PCB to draw the schematic to faciliate the job. We were used to order components from Toronto.I was surprise to find that the repair price was high. I remember to fix a monitor with C$80, and even inpection job costed C$20. At that time, renting a room costed only C$120, and the food cost per person was only C$200 monthly.
I left Calgary and returned to HK for a high-paid job, but now I plan to return.I would like to ask how about the repair business in Canada. What is the usual repair price? What sort of electronic equipments are used to repair?
I always go to Shenzhen (China) and get hugh repair information as well as components since Shenzhen is the electronic center in China.I'm the one capable of speaking Putonghwa, cantonese and English so I may be able to give help in doing the translation jobs concerning electronics as well as repair materials.
Leung Wing Kai
May 27, 2013 at 3:39 pm
Sometimes when we find the burnt resistor, it's likely the short diode or rectifier cause the problem.When I was in Canda, I was used to repair the monitor & power supply etc. I usually checked all those diodes & rectifiers to see if they were short. I also checked those big resistors to see if they were burnt or heated up before for passing high current.
If it was lucky I could fix the fault within minutes by replacing those short components.
Jestine Yong
May 28, 2013 at 9:30 am
Hi Leung,
Thanks for sharing your experience.
Jestine
Keith Ford
February 8, 2014 at 2:23 pm
great article! loved the light bulb description.
Raymundo Saura
February 8, 2014 at 11:32 pm
thanks for sharing sir Waleed Rishmawi and sir Jestine Yong thanks and GOD bless