Hi,
I have a surround system and one evening when I was out my girlfriend reported to me that there was bright orange coming out of the side. When I opened it I discovered that two of the three capacitors on the psu board had burned out. Also the red cable had melted at the end. All this was cleaned up with acetone and re soldered. These capacitors were replaced and the unit worked again for only a couple of months.

However I noticed the large capacitor on the secondary board was beginning to show signs of wear as it was bulging ever so fractionally. Now the unit has stopped working again and I am thinking of replacing the 400v capacitor. Does anybody have similar experience of how to repair this? I did manage to get a circuit diagram and checked the rectifiers and nothing else showed up wrong or open circuit about the transformer. I have little experience with fixing circuits I only have rudimentary knowledge of the applications but am good at practical repairs if I can diagnose the fault.

 

Hello,

What was the class of the original capacitors?
They would have been X-class, as it is in the mains circuit.
From the wiki:

Safety and EMI/RFI suppression film capacitors

• RFI/EMI suppression capacitors
• 
  
  
  Metallized paper RFI suppression capacitors (MP3) with safety marks for “X2” safety standard
  
  
• 
  
  
  Metallized polypropylene RFI suppression capacitor (MKP) for "X2" safety standard
  
  
• 
  
  
  Combined XY-RFI suppression capacitor
  
  

Electromagnetic Interference (EMI) or Radio Frequency Interference (RFI) suppression film capacitors, also known as "AC line filter safety capacitors" or "Safety capacitors", are used as crucial components to reduce or suppress electrical noise caused by the operation of electrical or electronic equipment, while also limited providing protection against electrical shocks.[73][74][75][76]
A suppression capacitor is an effective interference reduction component because its electrical impedance decreases with increasing frequency, so that at higher frequencies they short circuit electrical noise and transients between the lines, or to ground. They therefore prevent equipment and machinery (including motors, inverters, and electronic ballasts, as well as solid-state relay snubbers and spark quenchers) from sending and receiving electromagnetic and radio frequency interference as well as transients in across-the-line (X capacitors) and line-to-ground (Y capacitors) connections. X capacitors effectively absorb symmetrical, balanced, or differential interference. On the other hand, Y capacitors are connected in a line bypass between a line phase and a point of zero potential, to absorb asymmetrical, unbalanced, or common-mode interference.

• RFI/EMI suppression with X- and Y-capacitors for equipment without and with additional safety insulation
• 
  
  
  Appliance Class I capacitor connection
  
  
• 
  
  
  Appliance Class II capacitor connection
  
  

EMI/RFI suppression capacitors are designed and installed so that remaining interference or electrical noise does not exceed the limits of EMC directive EN 50081[77] Suppression components are connected directly to mains voltage semi-permanently for 10 to 20 years or more, and are therefore exposed to overvoltages and transients which could damage the capacitors. For this reason, suppression capacitors must comply with the safety and inflammability requirements of international safety standards such as the following:

• Europe: EN 60384-14,
• USA: UL 60384-14, UL 1283
• Canada: CAN/CSA-E60384-14, CSA C22.2, No.8
• China: CQC (GB/T 6346.14-2015 or IEC 60384-14)

RFI capacitors which fulfill all specified requirements are imprinted with the certification mark of various national safety standards agencies. For power line applications, special requirements are placed on the inflammability of the coating and the epoxy resin impregnating or coating the capacitor body. To receive safety approvals, X and Y powerline-rated capacitors are destructively tested to the point of failure. Even when exposed to large overvoltage surges, these safety-rated capacitors must fail in a fail-safe manner that will not endanger personnel or property.
Most EMI/RFI suppression film capacitors are polyester (PET) or metallized polypropylene (PP) film capacitors. However, some types of metallized paper capacitors (MP) are still used for this application, because they still have some advantages in flame resistance.[78]

https://en.wikipedia.org/wiki/Film_capacitor#Safety_and_EMI/RFI_suppression_film_capacitors

For safety, you must replace the capacitors with the correct safety class.

Bertus

 

X2 according to the spares I have, see photo 1 in situ, 1microF

 

I've replaced the three capacitors between the filters on the psu board and it worked for a couple of months.

 

Have checked power 240v

 

Have ordered a new 400v 180micro cap.

 

Still not working with the new capacitor. Any suggestions please?

 

The left hand pin only has a 0.2v in diode mode. The right pin 0.5v. How does one identify an equivalent linear regulator from the letters and numbers pls?

 

Hello,

There are two diodes in the package.
One is used for rectifying, the other for temperature measurement.
See the datasheet for more info.

Bertus