Pioneer QX40000 - When replacing bulb, shorted bulb to ground. No now display

ChopperCharles · 31st July 2011, 04:00 AM

So I'm a big dummy, I was replacing bulbs while the unit was on, so I could see which ones were bad. Aaaaaaaaand I was using metal tweezers. Guess who shorted it to ground? Yup. I'm a genius.

At any rate, teh display instantly went dark, but I can't find a blown fuse anywhere. There a bunch of fuses inside, but each one tests good.

Any ideas?

Thanks!

Charles.

Mooly · 31st July 2011, 10:26 AM

If everything else works then pick a bulb and trace back taking voltage readings from each bulb end to its final destination on the PCB.
Could be there is a bulb driver transistor, particularly if the display is dimmable etc or goes out in standby.

QX40000... whats that ?

Ronode · 11:17 AM

Is this a QX-4000, the Quadraphonic receiver from the mid 70's?
If so look for the 3 amp fuse that feeds the lights.
It should be labled "F2".
I think you have to take the bottom off to get to it.

Ronode · 31st July 2011, 12:27 PM

I was half asleep when I posted my first reply.
Didn't see you had checked the fuses.
If you measured the light circuit fuse while still in the holder your ohmmeter would see the transformer winding thru the light bulbs and show continuity even though the fuse is blown.
Did you pull the fuse to test it?

ChopperCharles · 31st July 2011, 02:58 PM

That was it, fuse was blown but I was reading through the transformer winding. Going to replace it with a fuse holder, those glass fuses are a bitch to solder to directly. I've got it back up and running now, thanks!

Charles.

sakis · 2nd August 2011, 01:31 PM

i dare to presume that you did other service things in the amplifier also .... if not you will have to sooner or later ...

ChopperCharles · 2nd August 2011, 09:23 PM

I deoxited all the pots and switches, and it plays again... but the right channel is louder than the left, and in a bass-heavy, breaks-up-at-louder-volumes kind of way. (ie, the left channel sounds correct, the right channel shouldn't be this way). Not the speakers. Not sure what's wrong exactly, but I was going to start by re-capping the main amplifier boards and head amp boards.

Charles.

ChopperCharles · 3rd August 2011, 01:57 PM

Note, it's only the front right channel that's behaving in this manner. If I switch to 4-channel mode the rear channels are the same volume and bass levels, and sound perfect. So I'm guessing the problem is in the amplifier board for the front channels.

Charles.

31st July 2011, 04:00 AM	#1
ChopperCharles diyAudio Member Join Date: Jan 2008	Pioneer QX40000 - When replacing bulb, shorted bulb to ground. No now display So I'm a big dummy, I was replacing bulbs while the unit was on, so I could see which ones were bad. Aaaaaaaaand I was using metal tweezers. Guess who shorted it to ground? Yup. I'm a genius. At any rate, teh display instantly went dark, but I can't find a blown fuse anywhere. There a bunch of fuses inside, but each one tests good. Any ideas? Thanks! Charles.

31st July 2011, 10:26 AM	#2
Mooly diyAudio Member Join Date: Sep 2007	If everything else works then pick a bulb and trace back taking voltage readings from each bulb end to its final destination on the PCB. Could be there is a bulb driver transistor, particularly if the display is dimmable etc or goes out in standby. QX40000... whats that ? __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

31st July 2011, 10:59 AM	#3
Ronode diyAudio Member Join Date: Jul 2005 Location: Racine WI	Is this a QX-4000, the Quadraphonic receiver from the mid 70's? If so look for the 3 amp fuse that feeds the lights. It should be labled "F2". I think you have to take the bottom off to get to it. Last edited by Ronode; 31st July 2011 at 11:17 AM.

2nd August 2011, 01:31 PM	#6
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	i dare to presume that you did other service things in the amplifier also .... if not you will have to sooner or later ... __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

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31st July 2011, 12:27 PM	#4
Ronode diyAudio Member Join Date: Jul 2005 Location: Racine WI	I was half asleep when I posted my first reply. Didn't see you had checked the fuses. If you measured the light circuit fuse while still in the holder your ohmmeter would see the transformer winding thru the light bulbs and show continuity even though the fuse is blown. Did you pull the fuse to test it?

31st July 2011, 02:58 PM	#5
ChopperCharles diyAudio Member Join Date: Jan 2008	That was it, fuse was blown but I was reading through the transformer winding. Going to replace it with a fuse holder, those glass fuses are a bitch to solder to directly. I've got it back up and running now, thanks! Charles.

2nd August 2011, 09:23 PM	#7
ChopperCharles diyAudio Member Join Date: Jan 2008	I deoxited all the pots and switches, and it plays again... but the right channel is louder than the left, and in a bass-heavy, breaks-up-at-louder-volumes kind of way. (ie, the left channel sounds correct, the right channel shouldn't be this way). Not the speakers. Not sure what's wrong exactly, but I was going to start by re-capping the main amplifier boards and head amp boards. Charles.

3rd August 2011, 01:57 PM	#8
ChopperCharles diyAudio Member Join Date: Jan 2008	Note, it's only the front right channel that's behaving in this manner. If I switch to 4-channel mode the rear channels are the same volume and bass levels, and sound perfect. So I'm guessing the problem is in the amplifier board for the front channels. Charles.

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