I bought a Pioneer SX-626 recently. I'm glad I checked the fuses before powering it up, as someone had done the old aluminium foil trick on them. So I replaced them all with the correct 2A ones, sure enough, they started to blow when powered up.
I traced the problem to the power amp board, since with the power amp fuses removed, the main fuse didn't blow. You can actually pull the pre/power jumper, and use it as a tuner/pre-amp. I wanted to get it going properly, so here goes the rest of the story.
I used the list of capacitors and transistors in this thread to place an order with Mouser. Kind of, I did substitute Nichicion KWs for the caps. I also ordered a replacement main power supply capacitor.
Here is a picture of the amp board on it's way out.
On the workbench, AKA the kitchen table, I was shocked to see ALL the power transistors as dry as a bone, there was no trace of heatsink compound left anywhere.
Here were are with new caps and transistors in place. The original output caps have a 4-pin design with two pins connected together. Since my new caps were only 2-pin, I had to make a link on the bottom of the board (blue wires).
But I wasn't done...
When I put everything back together, the amp still kept blowing a fuse. I researched another thread which mentioned the trimmers could go open circuit. I pulled mine off and tested them, and sure enough, there were a couple of bad ones. I elected to replace all of them, and since I couldn't find anything as large, I made up some little stripboard uprights with Bourns trimmers on, which as luck would have it, I had some 100R and 50K left over from another project.
With these in place, I was now able to set the center voltage and offset as normal. Here are some pictures of it all back together. Notice I had to use a rubber P-clip to hold the new main power supply capacitor in place, it's a lot smaller than the original. The flying white wires used to set the bias had their bare ends trimmed off, and were hot melt glued onto the output caps.
Lee.
I traced the problem to the power amp board, since with the power amp fuses removed, the main fuse didn't blow. You can actually pull the pre/power jumper, and use it as a tuner/pre-amp. I wanted to get it going properly, so here goes the rest of the story.
I used the list of capacitors and transistors in this thread to place an order with Mouser. Kind of, I did substitute Nichicion KWs for the caps. I also ordered a replacement main power supply capacitor.
Here is a picture of the amp board on it's way out.
On the workbench, AKA the kitchen table, I was shocked to see ALL the power transistors as dry as a bone, there was no trace of heatsink compound left anywhere.
Here were are with new caps and transistors in place. The original output caps have a 4-pin design with two pins connected together. Since my new caps were only 2-pin, I had to make a link on the bottom of the board (blue wires).
But I wasn't done...
When I put everything back together, the amp still kept blowing a fuse. I researched another thread which mentioned the trimmers could go open circuit. I pulled mine off and tested them, and sure enough, there were a couple of bad ones. I elected to replace all of them, and since I couldn't find anything as large, I made up some little stripboard uprights with Bourns trimmers on, which as luck would have it, I had some 100R and 50K left over from another project.
With these in place, I was now able to set the center voltage and offset as normal. Here are some pictures of it all back together. Notice I had to use a rubber P-clip to hold the new main power supply capacitor in place, it's a lot smaller than the original. The flying white wires used to set the bias had their bare ends trimmed off, and were hot melt glued onto the output caps.
Lee.
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