QED A 240 CD Can Anyone Pls Help With Repair - Page 2

Mooly · 4th March 2018, 06:39 PM

Quote:

Originally Posted by Rol G

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.

Rol G · 4th March 2018, 07:03 PM

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?

Rol G · 4th March 2018, 07:05 PM

Thanks I always get my components from a nice local shop Cricklewood Electronics.

Rol G · 4th March 2018, 07:18 PM

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.

Mooly · 4th March 2018, 07:29 PM

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.

Rol G · 4th March 2018, 07:38 PM

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?

Mooly · 4th March 2018, 07:49 PM

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.

Rol G · 5th March 2018, 04:42 PM

I got a bridge KBL08 for 75 p. Now the amp seems to work fine. Thanks so much for your patience.

Mooly · 5th March 2018, 04:48 PM

excellent.

Mooly · 5th March 2018, 04:51 PM

And don't forget to check the bias setting on the channel with replacement semiconductors fitted... follow the manual for procedure.

4th March 2018, 07:29 PM	#15
Mooly diyAudio Moderator Join Date: Sep 2007	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. __________________ Installing and using LTspice IV. From beginner to advanced. Help for Ruth & Dave

4th March 2018, 07:49 PM	#17
Mooly diyAudio Moderator Join Date: Sep 2007	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. __________________ Installing and using LTspice IV. From beginner to advanced. Help for Ruth & Dave

5th March 2018, 04:48 PM	#19
Mooly diyAudio Moderator Join Date: Sep 2007	excellent. __________________ Installing and using LTspice IV. From beginner to advanced. Help for Ruth & Dave

5th March 2018, 04:51 PM	#20
Mooly diyAudio Moderator Join Date: Sep 2007	And don't forget to check the bias setting on the channel with replacement semiconductors fitted... follow the manual for procedure. __________________ Installing and using LTspice IV. From beginner to advanced. Help for Ruth & Dave

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4th March 2018, 07:03 PM	#12
Rol G diyAudio Member Join Date: Dec 2008	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?

4th March 2018, 07:05 PM	#13
Rol G diyAudio Member Join Date: Dec 2008	Thanks I always get my components from a nice local shop Cricklewood Electronics.

4th March 2018, 07:18 PM	#14
Rol G diyAudio Member Join Date: Dec 2008	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.

4th March 2018, 07:38 PM	#16
Rol G diyAudio Member Join Date: Dec 2008	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?

5th March 2018, 04:42 PM	#18
Rol G diyAudio Member Join Date: Dec 2008	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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