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QED A240CD Blows Fuse on Powerup
QED A240CD Blows Fuse on Powerup
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Old 5th July 2008, 06:49 PM   #21
Nanook is offline Nanook  Canada
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Default Funky....

a couple of thoughts;
  • if you are having this much trouble identifying basic parts, you should stop
  • sreten made a suggestion to disconnect the transformer output from the amp, but you don't really understand things, so you are asking very basic questions, so you should stop and "re-group"
  • because you don't understand the basics you could seriously injure yourself--please stop working on this NOW!

Now I know this is "diyAudio" and DIYing can be fun, but I suggest that you stop working on getting this QED working. Not because it can't be done. You need to educate yourself on basic electronics, so you have a(at least) a very basic understanding of electricity and electronics. The transformer can push enough current that you can be seriously injured or worse ('').

If this was a "find" it will wait until you learn a little and maybe have tackled some basic projects on your own, or through evening "interest" classes at your local community centre or college or high school.

I am not trying to be overly critical, it is just that based on some of your questions, you simply have a non-existent understanding of this. You really need to take some time and learn some skills. It really is for your own safety I am making these comments. It is not personal, nor am I attacking your "intelligence". What I am suggesting is that it seems you are already "over your head". I would hate to find out that somehow you were injured working on this.

So put the QED away for now, and take a course, buy a good book on basic electronics (Radio Shack or Tandy used to have a really basic, but informative book for only a few $$), and gain a little confidence. If you need the amp fixed now, get it into a repair shop.

I'd still encourage you to take a course, regardless. Once you learn skills, nothing (except perhaps age...) can take that away form you.


stew
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Old 5th July 2008, 07:01 PM   #22
Funky971 is offline Funky971  United Kingdom
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I am not going to work on this amp on my own. I am very interested in amplification and am trying to learn about it. I do understand that electronics can be dangerous which is why I am working with a friend who knows what he is doing. I am just trying to learn as much about it as I can before I see him next week to test the transistors with a multimeter. If the transistors come up as fine I will try again to take it to a repair shop.
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Old 5th July 2008, 10:06 PM   #23
Nanook is offline Nanook  Canada
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Default Funky....ok, cool.

I just would really hate to see you get injured ...

If your friend is experienced, then I'm sure in person he can help you , and you'll end up learning. The Tandy book, if still available, is almost as basic as it can get. A bonus was that it was really cheap to buy.

I hope I didn't come across as condescending, I really wanted to underline the safety issues.


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Old 6th July 2008, 07:55 PM   #24
Funky971 is offline Funky971  United Kingdom
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thanks, i appreciate your concern. From experience with computers I have learned that it is important to know what I am doing before I try it and would not want to do anything too complicated until I am sure what I am about to do is right which is why I am getting in person help with this. I have also been researching into testing transistors for my own interest.
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Old 7th July 2008, 04:01 AM   #25
brainf is offline brainf  Philippines
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lohk... you are right, they are triple darlingtons. The first stage uses BC546 (BC556) , the Second stage BD140 (BD139) and finally, the Third Stage BD911 (BD912).

Funky971... Nanook raises some very good points about working with potentially lethal mains voltages present. I'm glad to note you are working with someone knowledgable and are using this opportunity to learn about amplifiers and transistors.

Good luck and let us know how it goes!
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Old 7th July 2008, 04:14 AM   #26
brainf is offline brainf  Philippines
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Here's a picture of the version I have, btw:
Attached Images
File Type: jpg dscn1366.jpg (90.6 KB, 435 views)
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Old 7th July 2008, 04:54 PM   #27
Funky971 is offline Funky971  United Kingdom
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Default Brainf

emailed you some more shots of mine internally. Mentioned in the email about the speaker connectors but I can see from here that you have the same options as me when plugging in speakers.
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Old 8th July 2008, 12:18 AM   #28
brainf is offline brainf  Philippines
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Thank you Funky.

Lot's of changes between version 1 and version 2 are evident in the layout and features but not in the speaker connections. You'll need to look for narrow profile 4mm banana plugs and just make sure they don't short each other out when plugged it. (Version 1 has output fuses visible in the back-right portion - just below the power cable, while version 2 lacks them).

But before you get to that stage you'll need to sort out the blowing fuses first. What fuses did you replace them with? (The markings on my board lists them as "1.6A Anti-surge" for a 220-240V mains voltage).

Assuming that the blowing fuse is of the correct rating, I'd try to rule out a shorted transformer by disconnecting the secondary windings from the board (the two yellow and two white wires), powering it up with a new fuse and see if it blows again. (If it does, you've got a shorted transformer which needs replacement). If it doesn't then the next place to look is at your output devices (as already mentioned by others here).
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Old 8th July 2008, 08:52 AM   #29
Funky971 is offline Funky971  United Kingdom
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Ok, thanks, the fuse in mine is the 1.6 amp antisurge. When I was trying to get the amp fixed I took it to two shops. The first one was more of a PA shop than a hifi shop. They opened up the amp and tried a new fuse however they did not have the exact one (I think it needed a T type fuse and they put an F type in instead). They put a different rating in because they said it would compensate for it being the different type. That one blew so he checked the wiring of the plug and tried another one which also blew. He then realized it was a hifi amp and told me to go to the second place which wouldn't even look at it. I am going to go to maplin this week and get some of the correct fuses.
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Old 8th July 2008, 09:40 AM   #30
jaycee is offline jaycee  United Kingdom
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Judging by the black mark on the fuse in the picture, it is blowing due to a fault - DONT simply put a new fuse in, you will be causing further damage!
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