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Old 18th January 2010, 09:45 PM   #1
OHjim is offline OHjim  United States
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Default Apex Senior advice needed

I have a 1.5 year old Apex Senior amp that blew a cap. It's a 6800uf 100v cap in the upper right corner of the second picture here: The Apex Senior Subwoofer Amp

I have this amp hooked to an A/D/S MS4 / SW500 sub for my HT (12" 4 ohm). I have turned this up a few times to see what it could do, but since I usually watch at night while the kids are sleeping, I don't have much chance to crank it. The power fuse blew the other day while listening to TV.

I put it on my bench and replaced the fuse, plugged it back in, heard a buzzing sound that sounded like it might be coming from the transformer, but before I could tell anything, POW, the lid blew off the cap.

Questions:
1) Could a defective cap cause the transformer to buzz?
2) If I replace the cap, would a good assumption be that the same thing would happen again?
3) Would the transformer be bad and blow the cap?
4) Anything to check to see if something else is wrong?
5) Is any 6800uf 100v cap OK to use or does it need to be an audio type? I am having trouble find an exact replacement - 30 x 65mm.
6) Do I have to replace in pairs, all four, or can I just replace the one that blew?

I talked to Steve at Apex Jr and he does not have a tech anymore and that he's not seen these caps blow - just the 80v ones. Any help would be much appreciated as I am not an EE but a dreaded ME - I know enough to be dangerous.

Jim
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Old 18th January 2010, 10:49 PM   #2
Spiny is offline Spiny  United Kingdom
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Quote:
Originally Posted by OHjim View Post
Questions:
1) Could a defective cap cause the transformer to buzz?
Yes, Short circuit cap will blow fuse

2) If I replace the cap, would a good assumption be that the same thing would happen again?

Check the bridge rectifier before replacing the cap, Use a meter in diode test mode. It may be one or more has failed, if the bridge seems ok build a llightbulb tester and plug the amp into that. See various threads, basically a 60/100watt bulb in series with a power socket, Should not stay lit! if it dose the amp is drawing excessive current

3) Would the transformer be bad and blow the cap?
Unlikely
4) Anything to check to see if something else is wrong?
See answer to 2
5) Is any 6800uf 100v cap OK to use or does it need to be an audio type? I am having trouble find an exact replacement - 30 x 65mm.
Audio type not needed, this is a PSU cap. Make sure the ripple rating is suitable.
6) Do I have to replace in pairs, all four, or can I just replace the one that blew?
Replace the blown one, The Lightbulb gadget will save the amp if there is another fault
Description of the Lightbulb tester

Last edited by Spiny; 18th January 2010 at 10:58 PM. Reason: Link to good description of the lightbulb tester
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Old 19th January 2010, 12:59 AM   #3
OHjim is offline OHjim  United States
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Thanks Spiny. I will try that light bulb trick - basically in line with the power wire (usually black), if I read that right. How do I know what ripple rating I need on the cap? Does the schematic provide a clue?
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