Pioneer SX-1280 Problem with Power Protection Board

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DraKnight13

Active Member
Hello, I got a Pioneer SX-1280 a while back not working. Unit turned on, but no sound can be heard from it. The power supply and power protection board was recapped one before, but the previous guy did very weird stuff (instead of using 10 ohm resistor, he used a combination of resistors in series and parralel etc...). Because of that, I just go ahead and replaced every single components on both the power supply board and power protection board. Now unit turned on, still no sound. After measuring the voltage coming in (or out) of the power protection board, I found out that PIN 3 and 10 only have 60V instead of 76V, and pin 4 and 9 only have -60V instead of -76V. Does that mean the filter capacitors need to be replaced. Sorry I am quite new at this and at loss at what to do next.
Thank you and please let me know.
 
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Are you on the DBT, or direct to the power line.

what are the regulated voltages?
 
It is on the DBT, voltage is 120V. When I first turned it on, there is a bit of smoke, the R23 on the power supply board burned. The DBT was bright for a bit, but now it dim all the way stable while I was doing the measurement.
 
If it's in protect maybe the protection board is working as intended... What is the voltage on both AWH-074 boards pin #7? And what about those crazy diode strings on those boards?
 
Relay on the power supply works, relay on power protection board didn't. I didn't touch the power amplifier board yet so I will get right on it.
 
If R23 burned one or both of the amplifier boards has a problem. Those are the only places that R23 supplies.

Craig
 
when I go measuring everything, Pin number 7 on power amplifier doesn't have any voltage. The rest of the voltage is there, but always lower than the schematic. It seems to be running stable. The voltage from the the power amplifier board is this:
  • Pin 1: -32V
  • Pin 2: 32V
  • Pin 6: 62V
  • Pin 5:-62V
  • Pin 10: -65V
  • Pin 16: 65V
 
Fix the power supplies first, nothing you see at the Power Amp will be reliable until the power supplies are correct. First you must see if the inputs to the power supply pcb are correct. Remove R23 for now. Post 2 started you in the right direction . . .
 
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DraKnight13 said:
what should I look for when I remove the resistor???
Click to expand...
Whatever caused it to burn has not yet been repaired, if you replace it it may burn again. I just wanted you to leave it out for now. You can troubleshoot the power supply with it out, for now.
 
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R23 powers the driver sections of the power amps. There is obviously something very wrong there. Fix that first, then replace R23. If you replace it now it will get destroyed again. With the mains plug pulled, measure the resistance of R23 (prolly more than 10R) and the resistance from pin #8 of AWR-057 to ground.
 
Sorry for the mistake. The one that burned was R24, R23 is fine. Resistance of R24 is 5 ohm instead of 10, so I am guessing too much current going through it causing it to blacken? Now I have measure the voltage coming out of the transformer (or going in) they are all lower. There is a big resistor in the Fuse Assembly board (AWX-126) that was supposed to be 1.2 ohm, but the guy who did the job before me put in a 1.8 ohm. Would that be a problem????

Now from my schematic reading skill (which as evident, abysmal) the electric first going through the fuse assembly board, then go into the power supply board, then to the transformer to the power protection board???? Is that the correct sequence????
 
After measuring everything, I traced it back to the source, which is the voltage coming out of my DBT: only 100V give or take. I know voltage coming out of the outlet is 120V, I don't know what can cause the voltage to drop through the DBT. Would the type of bulb cause this? Due to the inability to get any incandescent bulb that more than 40W, I am using this bulb
90559977_2635795939988572_4362616076043812864_n.jpg

Hopefully this isn't a problem since this is the only 100W bulb I have. I have called multiple place and there isn't seem to be 100W bulb anywhere for sale. If this is a wrong type I may have to resort to buying them from online store.
 
DraKnight13 said:
After measuring everything, I traced it back to the source, which is the voltage coming out of my DBT: only 100V give or take. I know voltage coming out of the outlet is 120V, I don't know what can cause the voltage to drop through the DBT. Would the type of bulb cause this? Due to the inability to get any incandescent bulb that more than 40W, I am using this bulb
View attachment 1805783

Hopefully this isn't a problem since this is the only 100W bulb I have. I have called multiple place and there isn't seem to be 100W bulb anywhere for sale. If this is a wrong type I may have to resort to buying them from online store.
Click to expand...

The purpose of the DBT is to limit power coming into the unit under test to protect it, it does this by limiting the current and dropping the voltage, what you have determined is that the DBT is working correctly. That was the point of the first question in post 2. All of the ac voltages on the secondary side of the transformer will be low while on dbt.

DraKnight13 said:
Sorry for the mistake. The one that burned was R24, R23 is fine. Resistance of R24 is 5 ohm instead of 10, so I am guessing too much current going through it causing it to blacken? Now I have measure the voltage coming out of the transformer (or going in) they are all lower. There is a big resistor in the Fuse Assembly board (AWX-126) that was supposed to be 1.2 ohm, but the guy who did the job before me put in a 1.8 ohm. Would that be a problem????

Now from my schematic reading skill (which as evident, abysmal) the electric first going through the fuse assembly board, then go into the power supply board, then to the transformer to the power protection board???? Is that the correct sequence????
Click to expand...

The 1.8Ω resistor in place of the 1.2Ω resistor will make the light bulbs dimmer.

I will get back to you on the power flow through the system.
 
So now if everything is working correctly, I can take it off the DBT and test??? Because right now the voltage isn't right and doesn't seem like the relay on the power protection board isn't engaging.
 
I took a leap of faith, and it seems to be working properly, I don't know what exactly cause the resistor to burn in the first place, but it isn't doing it now. Still get no sound from it, but I think I install the relay on the power protection board wrong. I really have trouble with remove these boards from the chassis due to the amount of wire that need to be desolder. I will try to do that and come back with the result, but most likely with more question.
 
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