Pioneer SX-1280 Protection Relay Cycling On And Off

huh?

sx-1280 awh-074L vr1 150k 25 turns offset adjust 652-3296P-1-204LF

do yourself a favor, get the multi-turn offset pot.... far less touchy of an adjustment...


sx-1280 awh-074L vr2 100 ohms 1 turn idle current 652-3386H-1-101LF
 
Awesome!! I posted this before looking them up. When looking at the catalog page, I noticed they were single turn and was perplexed. Thanks a ton.
 
I wanted to thank everyone again for the help on this project and give an update.

I just finished the pleasure of tickling the dragon. DC offset to within 2mV of the sweet spot and Idle current within 0.1mV. Built a DBT to bring the monster alive after the re-cap on the Power Amp Boards and main filter caps. turned it on with a 100W bulb in place and it did just what was described in the threads I reviewed as I was setting it up. Full bright monentarily then dim. I love the protection and will ALWAYS use it.

I built new busses for the chassis grounds of the new screw terminal main caps based on a design I saw posted by EchoWars. I've included pictures. I saw previous questions regarding the orientation of the main caps when reinstalling. For my application, all caps needed to be installed with the (-) terminals facing the front of the unit to match what was taken out and keep the terminations of the White, Red and Orange wires in the same spot.

Thanks again to all. The unit is up and running again and sounds better than ever. The only thing I noticed was the heat generated by Q1 and Q2 on the power supply board, AWR-157. These get so hot, you cant hardly touch them. Is this normal?
 

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Thank you, Zebulon1! Cleaning the faceplate, knobs, and buttons. The wood parts are ready to go.

Great project. My first real re-cap / restoration, now i'm hooked. I have a line on a Marantz 2500 with possible gremlins. My wife thinks I'm nuts, but i keep telling her she knew before she said "I do".
 
How hot are the Q1 and Q2 on the power supply boards supposed to get on the SX-1280? Iv'e read other posts claining they get hot, but man, you cant keep your finger on these puppies.
 
The whole stabilizer get pretty hot. If you upgraded and restored to the MTF list. No worries.
 
If you can fit in additional heat sink area on the hot transistors, the unit will reward you with longer psu life...
 
Hi
I'm also recapped my pioneer sx1280 but when checking the voltage on power supply the -68v is -70.5 the +68 is good. Should I be concern with the -70.5 voltage?
If yes where I should be looking to resolve the problem, I was wondering if i could install trim pot but don't know where would be good spot for it.
Can any one help me with that.

Thanks
 
d8 q4 q2
you could try swapping d7 and d8 . then see what happens ..or best first check voltage across them .they should both be same voltage .
 
I'm also recapped my pioneer sx1280 but when checking the voltage on power supply the -68v is -70.5 the +68 is good. Should I be concern with the -70.5 voltage?
Not at all, leave it alone, it is only 3.7% out
You are comparing 2 zener references D7,8 which are 5% and then the feedback resistors that are 5% too, R9,10,11,12. It could be worse than what you have already.
If you measure +/-32V you will find the differences in tolerances in D9,10 too
Out of interest if you want to tighten up the tracking, then you could use tighter tolerance zeners 2%, resistors 1% or better. If you want to trim, look at how they did it on the sx-1250, basically replace R11,12 (15K) with a ~14K R and a 2K pot, but pots are not as reliable as a fixed R.
 
d8 34.1
d7 -32.8

d10 32.8
d9 -32.5

plus all the transistors on that board are new and the diode too
 
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like rcs16 says it will be fine as is .
the difference in zeners is 1.3v so that is part of why voltage is slightly higher on the -68v
 
One more question guys
What should be the correct voltage on pin 14&15 on power suppy board (157) i'm getting 10.7Volts
My light bulbs are getting 10.7 volts I think they are 8v
 
pin 8&10 on 126 board correct
wheer i should be looking to fix this issue ? This is last issue on this baby after that music time >>>>>>ya Huuu
 
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