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QED A 240 CD Can Anyone Pls Help With Repair
QED A 240 CD Can Anyone Pls Help With Repair
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Old 4th March 2018, 06:39 PM   #11
Mooly is offline Mooly  United Kingdom
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QED A 240 CD Can Anyone Pls Help With Repair
Quote:
Originally Posted by Rol G View Post
Thanks, yes the pair of bd911/12 are short between all three contacts, the 139/140 drivers are not, but i changed them because in circuit the pair of the blown channel showed different resistance to the pair on the good channel.
Fair enough.

As you show as UK based you could do worse than to get the BD911/912 and BD139/140 from CPC (part of Farnell). Don't buy parts from ebay as many are fake.
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Old 4th March 2018, 07:03 PM   #12
Rol G is offline Rol G  United Kingdom
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Thanks, The capacitor fed by the bridge, is that one of the 2 large blue 4700 40V [ C8 ]? can i test that one across the bridge pins. i already cut off the bridge so i can solder in a replacement tomorrow, there is no short across any of the 4 pins . does that mean the cap is ok?
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Old 4th March 2018, 07:05 PM   #13
Rol G is offline Rol G  United Kingdom
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Thanks I always get my components from a nice local shop Cricklewood Electronics.
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Old 4th March 2018, 07:18 PM   #14
Rol G is offline Rol G  United Kingdom
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Hi again. with the bridge removed, the plus pin and the AC pin next to it [that leg started burning the bridge] both show a short to ground.
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Old 4th March 2018, 07:29 PM   #15
Mooly is offline Mooly  United Kingdom
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QED A 240 CD Can Anyone Pls Help With Repair
The cap is probably OK but with a bulb tester there would be no problem even if it were not.

Because the amp runs on a dual or split supply (giving a plus and minus rail) there will be two reservoir caps... the big blue ones

My circuit doesn't seem to show much of the power supply at all but it will be text book stuff.

The short you read on the bridge shows that one of the diodes has failed.
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Old 4th March 2018, 07:38 PM   #16
Rol G is offline Rol G  United Kingdom
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Thanks, I disconnected two transformer wires from the board, the 2 which go to the ac tags of the bridge there are short circuits between the pair and between each of the two and ground. Does that mean the transformer is gone?
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Old 4th March 2018, 07:49 PM   #17
Mooly is offline Mooly  United Kingdom
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QED A 240 CD Can Anyone Pls Help With Repair
No, the transformer will have a very low DC resistance between the connections on the secondary. All normal

It will also have a surprisingly low resistance between live and neutral as well. Again normal.
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Old 5th March 2018, 04:42 PM   #18
Rol G is offline Rol G  United Kingdom
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I got a bridge KBL08 for 75 p. Now the amp seems to work fine. Thanks so much for your patience.
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Old 5th March 2018, 04:48 PM   #19
Mooly is offline Mooly  United Kingdom
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QED A 240 CD Can Anyone Pls Help With Repair
excellent.
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Old 5th March 2018, 04:51 PM   #20
Mooly is offline Mooly  United Kingdom
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QED A 240 CD Can Anyone Pls Help With Repair
And don't forget to check the bias setting on the channel with replacement semiconductors fitted... follow the manual for procedure.
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