Pioneer SX-1280 Restoration in Malta

To make sure that the +13V will never go up more than 13V (currently the output of the Pioneer regulator is around 14V) which, if for some bizarre reason it spikes over 15v, it will end up frying most of the chips found in the tuner (iirc one of the chip's maximum voltage input is 15v).... I have added a linear regulator, LM317; should any of the transistors fail, all of the 13V circuits would be protected. I bought this for a mere 3$ from ebay. Has a trimming pot too.

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New thermal fuse too. Couldn't find the original one ( IIRC 109 degrees celcius @ 15amp) - I have installed one which cuts off at 121 degrees celcius.

Thermal fuse.JPG
 
(I'm listening to Dire Straits on my SX1250 while reading this.)

It looks like did a great job and it makes me happy to see receivers like this preserved.
 
PabloX - thanks! i still have to replace all the transistors and diodes found in the amplifier boards.... i wish to own a 1250 someday.... but out of budget for now. spent a lot on this 1280
 
You do realize that the soft start resistors (shown floating) have to be in good contact with the thermal fuse for it to do its job?
probably best to have both mounted well above the pcb surface so that if there is another PS fault that the pcb does not burn
 
rcs16 - yes and by right there should also be some thermal paste too. afterall, the scope ot the thermal fuse is to protect the resistors from burning
 
Awesomeaudio - the Hour meter is patched after the power switch since the one I bought needs 230VAC to operate. You would have to trace the wires like i did, or else you can find a 24V (usually they would have a wide range, say 10V to 50V) one and stick it in parallel to C20 on the power supply regulator board; it should not consume much current; presumably some few mAs (IIRC mine is around 0.3W). it starts counting when the receiver is on to indicate the elapsed time on the capacitors - not too critical, but it's nice to know how much the receiver has worked after the full restoration.
 
One thing i never liked in Pioneer receivers (and possibly other receivers) is the lack of earth present. These hifis, especially the 1280 and other high end pioneer with exposed heatsinks, could potentially possess a risk of electric shock should anything bizarre involving the live wires or the main power switch happens inside the receiver. So i proceeded to replace the original chord with a 3 core cable. While doing so, i installed an EMI filter, shown below. This was salvaged from an old computer power supply. The bottom is insulated with thick clear perspex and i have further insulated the thing using kapton tape. On top of this, a layer of black insulating tape was applied.

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Found the perfect slot to put this filter in the 1280! Neatly done. Im still waiting for the signaling transistors to arrive, so that I would refurbish the amplifiers.


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Amplifier components arrived today - All semiconductors found in each amplifier, will be replaced with new ones, including the dual transistors (2SA979, 2SC2291).

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The newly rebuilt amplifier board. The only 2 things that were not replaced were the biasing diodes and the resistors.

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