Pioneer SX-1250 Restore - Some Heat Q's

ivandezande

AK Subscriber
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Just went through an abused but working 1250 (a crappy DJ owned it for several years way back) and I replaced all caps many transistors and a few zeners, but now I wondering about heat. The heatsink on the stabilizer board gets very toasty quickly, and the resistors above the main diode bridges do as well. Is this something I should be worried about and try to remedy?
 
Just went through an abused but working 1250 (a crappy DJ owned it for several years way back) and I replaced all caps many transistors and a few zeners, but now I wondering about heat. The heatsink on the stabilizer board gets very toasty quickly, and the resistors above the main diode bridges do as well. Is this something I should be worried about and try to remedy?
I would rebuild the entire stabiliser board.
There is a list somewhere here for that.
The nature and design of the stabiliser board means there is a lot of heat produced as a result of the regulation.
 
You replaced the bjts and ecaps already in the PS, the heat is not going to go away, all you can do is to minimize component op temps, like adding more/bigger heatsinks to the series pass bjts regs to lower their Tj which improves reliability.
You could go nuts and replace everything as Kev suggests for a piece of mind & improved long term reliability, predicting when a film or ceramic cap will fail is in the lottery dept.
 
One of the hotter devices on the stabilizer board, and a potential way to help cool it:

SX-1250StabilizerBoardHeatSink01.jpg
 
predicting when a film or ceramic cap will fail is in the lottery dept.
Which is what caught me out on that 1250 I was working on......
So really, everything is becoming suspect these days, I used to rule out ceramic caps, but I have found a few shorted and intermittent ceramics lately...so this is now part of my failure mode when looking at problems in circuits..
 
everything is suspect but as for failing, only time will tell. :)
Basically fix them as they fail.
Even new components fail, the bath tub curve on comp reliability.
I once worked at a HP lab, had a EE who's sole job was component reliability analysis and regulatory certification. We hand him our design BOM's, he'd have to okay every comp, assess risks, come up with reliability numbers. Top of the list was moving parts, ecaps :) were forced to use kemet fused tantalums, just in case of a assembly reversal and possible fire.
finding caps failing anywhere can be a challenge esp if they fail open or way out of spec. RF sections are a PITA to fix
 
When I did mine I also added a small heat sink to it however I bought it new back in 1976 and never had a problem with it. I went thru it in 2016 so no problems in 40 years with regular use! The heat must not have hurt anything but it gave me a little piece of mind with an additional heat sink. FWIW.

An infa-red heat gun is a good tool to own.

Bob
 
IR heat guns are great tools to own, cheaper thermocouples but not as accurate
rule of thumb every 10C rise in Tj reduce the life by 1/2
 
As other posters have said, it will run hot. Around 175F IIRC is normal in 75F ambient. It will likely run like that for another 45 years with new transistors on it, if you plan to use it regularly longer than that I'd suggest restoring it again in 2060.

More important IMO is to ensure adequate airflow, some of these were operated in closed cabinets, sitting on shag carpet, things stacked on top, ... those stabilizer boards took it on the chin as did the PS boards and we occasionally see photos of the crispy critters, ... surprising that they survived.
 
It was custom made from heat sinks salvaged from other devices. Scrapped PCs (including power supplies and main processor core cooling packs) will yield a lot of good material for these projects. There are many choices for new heat sinks as well, but in such a situation they would also require customization to fit. Fortunately, aluminum alloys machine pretty easily.
 
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