SX-1010 advise

unclebort

Active Member
After successfully repairing two SX-780s and not winning the AK SX-1010, I decided to try repairing a dead SX-1010. I am certainly no expert at electronics repair, but I wanted to try anyway.

The receiver does not power up. When turned on, the relay will click on, then click off after a few seconds. None of the lights light up and no fuses are blown. The only clue visually is that the power supply board has been running hot. I have a service manual, and the voltages on the power supply board check to within a few tenths of a volt.

I am hoping some one here can give me a clue as to how to proceed.

Tom
 
Definetly looks like those resistors have been getting pretty hot. One of the capacitors looks bad too. The one with the funky looking top where it appears to be bulged out.

Im sure echowars can chime in on what you could do next.
 
I would resolder the parts on that board. They may read correct from the top but not making a connection due to cold solder joints will throw your voltages down steam out of whack.
 
Not sure, but it looks like those resistors are new--smooth, shiny, uniform color, unlike the circuit board. Likely someone replaced them, but didn't fix the problem, some thing overloading the power supply. In fact, that board looks so charred, it may be n.g.

Dan
 
Classic Pioneer discolored circuit board. Resolder the components on that board like Wards said. The board should still work, but you'll want to beef up that heat sinking for those regulators...they run hot as a pistol.

I think every 1010 in use has a discolored regulator board like that. My 838 does...

TP
 
Hello, and Thank You for the replies!

I have done a little more digging into this thing. I have resoldered the regulator board and replaced the suspicious looking caps. The voltages on the regulator board check out fine. As for the lights not lighting, playing with the dimmer switch brought them back on.

I checked the DC offset for both channels before the relay. The right channel was 9mv. I did not get a reading on the left. The output transistors tested the same for both channels. I did connect an old speaker to the right channel before the relay and I did get sound. I believe the problem is somewhere in the left channel amplifier. I also connected the preamp outs to another amplifier and the preamp and tuner are working fine.

B3Nut, the parts for the SX-780 are installed and that receiver is working great! All I need to do now is recover the case. Thanks again.

Tom
 
I still need to send you that other foot that fell out when I was packing that stuff to send! DOH! :D

TP <- drops stuff

PS - I found a place that has affordable STK-0050's... www.electronix.com. Another new member here pointed it out to me, so I gave 'em a shot. Less than $6 apiece...ordered a couple, got a 780 a couple weeks ago at GW that I'm going to try them in.

TP
 
I checked the DC offset for both channels before the relay. The right channel was 9mv. I did not get a reading on the left. The output transistors tested the same for both channels
It does kinda sound like the driver board has problems. The print is marked with a few voltages, but since one channel seems to function and one doesn't, you can compare voltages from side to side. I'd suggest starting with the drivers and work your way back into the amp, comparing voltages with power on, or checking individual components with power off.

I know it's a PITA, and with the 1010 you will have to unbolt the driver boards and output heatsinks and flip the heatsinks over out of the way...bring careful to use something to insulate the whole deal so it doesn't short (I just stuff some rags in there to prevent sparks). Watch where the wires enter the driver boards too so that you don't short 'em.
 
Thanks for the reply EW.

Well, I think I am making some progress. I have checked both driver boards. I could not find anything wrong. Both the right and left boards check the same, except I was getting no DC offset reading on the left channel. All diodes and transistors check out the same on both boards. As a last resort, I disconnected the wire from the left driver board. I am now getting a DC offset voltage of about 17mv out of the left channel. I can also get sound out of the left channel. I now believe the problem is on the protection circuit board.

My only problem now is that in moving the heat sinks, I broke one of the STV-3H varistors that is attached to the heat sink. I did remove the screw before moving the heatsink, but the wire broke anyway, and right at the varistor. Is there any way I can find a replacement / substitute?

I actually think I can now get this thing to work again.

Tom
 
Hey B3Nut, if one were to replace those power regulators using todays new regulators, would they operate a lot cooler or would I have to beef up the heat sink as you stated.
Polar Bear





Originally posted by B3Nut
Classic Pioneer discolored circuit board. Resolder the components on that board like Wards said. The board should still work, but you'll want to beef up that heat sinking for those regulators...they run hot as a pistol.

I think every 1010 in use has a discolored regulator board like that. My 838 does...

TP
 
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