I got one Sony Surround System TA-AV550 with the complaint that it was intermittent and crackling noise is heard inside. Tested it on my table and heard relay chattering.
As usual, I opened the set and subjected it for a thorough cleaning and visual inspection and removed the amp board and power supply board for inspection on its reverse side:
Noticed that there were several dry solder joints on the main board, power supply board and amp board. Did a thorough retouching all the points on the board. Saw the primary power supply AC transformer was in bad shape. Checked the bridge diode and found it has leakage between the two AC inputs (See Reading on the Multimeter)
I connected the Transformer to mains and allowed it to be on for a few minutes without any load on it. The reading was 0-10V AC. Noticed that the TX was getting hot, indicating partial short inside. Now the problem was to know what could be the real secondary voltage for this? There was no free circuit diagram for this model in the web. So, I decided to take a chance with a 0-12V, 1A TX that I had in stock. Replaced 5 electrolytic capacitors, the defective bridge diode, and also the AC filter capacitors connected across the rectifiers. Since, the relay was operating on 12V, and I saw a few transistors and zener diodes which are for voltage regulations, I connected the transformer and fit it on one screw of the other large TX, as there was enough space between the power supply board and the large TX.
Switched on the set, it worked perfectly well! No more chattering of the relay or other noises! I ran the set for a few hours, it worked just fine! Another job done satisfactorily!
This article was prepared for you by Parasuraman Subramanian from India. He is 66 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.
Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.
P.S-If you enjoyed reading this, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!
You may check on his previous repair article below: