Pioneer SX-9000 Blows Left 3A fuse. Help Please!

OK. I walked away from the unit for awhile to clear my head of it and went on to some other projects. This morning I decided to give it one more shot after an idea came to me. Why was it drawing so much current? I checked everything in the past and made notes in my head to what I had done but still no progress. Could it be a bad pot and I have to pull all of them from the board and check them that way? I decided to pull the VR3 and VR4 50K pots completely this morning and measure them against each other to see what the difference was. When I hooked up my DMM to the pulled VR3 50K pot it would read and beep one way while turning the control but not the other way. I thought it can't be that simple. So I measured the pulled VR4 50K pot and it measured and beep BOTH WAYS while turning the control adjustment. Dead short found? Hmmmm.... So I had some 50K pots in stock and I replaced the two pots with Bourns 50K pots by extending the leads and soldering them in. Plugged the unit into my DBT and the lamp was not lit at all. Plugged in the speakers and same thing. No bright light!! Turned up the volume and sound it both channels. :biggrin:

All this time and finally progress!!! :banana:

I did notice the FM lamp lamp does not come on so I need to check it to see if it is burnt. Also, I need to see how to adjust the voltages for the pots. The VR3 and VR4 are both new and I left centered when I installed them. The two others on the board (VR1 and VR2) I did not change out so they are original. I do not see a procedure in the service manual on how to set the pots. Any help would be greatly appreciated.
 
vr1 vr2 are to set centre voltages .
vr3 vr4 are to set the idle currents .

centre voltages should be roughly half of b1+ b2+ and measured at collectors (cases) of the output transistors .its marked c+ in schematic .

as for idle bias the manual looks wrong to me ..it says 1.4 amps shared between both channels .. way over the top .
i would think more like somewhere in the region of somewhere between 10 and 20ma each channel measured at the fuse-holders . fuses removed and substituted for an ammeter . i seem to remember the last one i did was happy about 12ma .

also i find with this circuit design its best to use 2 multi-meters as one setting can affect the other . so one for centre voltage the other for bias .
 
Thanks guys for all the help.

I will try to set the voltages like you suggest Pete. I will post the results. :thumbsup:
 
Hello, as a fresh reader, I have a polite question? The patient is a Pioneer SX9000, for 15-20 minutes after switching on, you can hear (from time to time) in the loudspeakers as if there was a storm in the distance, atmospheric discharges - where to look for the reason, can they be power transistors?
 
Hello, as a fresh reader, I have a polite question? The patient is a Pioneer SX9000, for 15-20 minutes after switching on, you can hear (from time to time) in the loudspeakers as if there was a storm in the distance, atmospheric discharges - where to look for the reason, can they be power transistors?

Probably not the power transistors. It's a Pioneer so it's loaded with known problem transistors (see the worst transistors sticky in Solid State).
Compare your service manual parts list with the first few posts in that thread.

You might get better visibility if you start a new thread.
 
Hello, thank you very much for the hint.
I do this hobby, it will be a while before I start with it and I will probably come back with questions, thank you again.
I am asking for understanding in matters of language (grammar), I do not know English well - my language is Polish. Best regards
 
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