Pioneer SA-1000 keeps burning R1 330ohm on power supply

[Dave1027]

Here's an identical issue: Burning resistor ( SA1000 ps board)

Looks like he did the same thing, recapped and new transistors. Then found out his transistor subs wasn't right. Check the transistors you substituted for the Differential tails and VAS (2SA572 and 2SC627).

 

[Brownie Mix]

Here's an identical issue: Burning resistor ( SA1000 ps board)

Looks like he did the same thing, recapped and new transistors. Then found out his transistor subs wasn't right. Check the transistors you substituted for the Differential tails and VAS (2SA572 and 2SC627).

I will check that. I saw the same thread. thanks

 

[Brownie Mix]

What @Dave1027 said ... also, do your transistor subs have the same pin assignments (ECB, or other)?

they are all ECB and I made sure to check old pin outs as I replaced. also compared with the screen-printed boards.

 

[Dave1027]

Maybe the new transistors are passing more current than the old? What model transistors did you install? Are they compatible substitutes? Do you still have the old transistors? If so swap them back in and see if R1 cools down.

 

[Brownie Mix]

Maybe the new transistors are passing more current than the old? What model transistors did you install? Are they compatible substitutes? Do you still have the old transistors? If so swap them back in and see if R1 cools down.

I think they were 992. I’ll check when I get back. I do have all the old transistors as well.

 

[Brownie Mix]

Pull the wire from 13 and see if the situation changes. It should have no current draw worth talking about with it off but lets confirm.

Also can you give us the voltage drop across the 330 ohm resistor?

Okay so pulling 13 pin lead off doesn’t toast R1 330ohm resistor. I put the lead back on it fired it up and one side resistors 41 V. The other side is -8 V.

 

[gadget73]

Well that clears what's on the power supply board. Problem is on the power amp board somewhere.

I'm assuming thsts -41 and -8? Both should be negative

 

[jheu02]

I think I saw that a replacement for the 2SA572 was KSA1220. So, IF you replaced it with KSA992, that is an incompatible replacement due to current handling (Ic).

I successfully replaced it with 2SA1507T in an SX-1000TW (actual model was Allied 395). The 2SC627 I replaced with 2SC3902T.

 

[Brownie Mix]

I think I saw that a replacement for the 2SA572 was KSA1220. So, IF you replaced it with KSA992, that is an incompatible replacement due to current handling (Ic).

I successfully replaced it with 2SA1507T in an SX-1000TW (actual model was Allied 395). The 2SC627 I replaced with 2SC3902T.

Okay I’ll check that out. Thanks!

 

[Brownie Mix]

I think I saw that a replacement for the 2SA572 was KSA1220. So, IF you replaced it with KSA992, that is an incompatible replacement due to current handling (Ic).

I successfully replaced it with 2SA1507T in an SX-1000TW (actual model was Allied 395). The 2SC627 I replaced with 2SC3902T.

Okay so I don’t have any 1220’s so I put the originals (572’s) back in the main amp board and still burning 330 ohm resistor. Ugggg. This is frustrating.

 

[Richard P]

throwing parts at it isn't the best approach. Pull out your multimeter and start troubleshooting the section of the amp circuit i pasted in post 14 . . . Q1 ~ Q8, D2 and D5 are all fed from pin 13/pin23. Good place to start.

 

[Brownie Mix]

throwing parts at it isn't the best approach. Pull out your multimeter and start troubleshooting the section of the amp circuit i pasted in post 14 . . . Q1 ~ Q8, D2 and D5 are all fed from pin 13/pin23. Good place to start.

Will do. D1 & D5 are replaced. But I will check them and all the transistors. Thanks. Appreciate all the help

 

[Richard P]

Look for solder bridges on the foil side of the board as well . . . easy to do when recapping.

 

[petehall347]

try lifting one end of these resistors start with the 68 ohm one .. then if still high current draw do same for other channel . you could of course do resistance checks with the power off for both sides of each resistor to ground .

 

[Dave1027]

Well that clears what's on the power supply board. Problem is on the power amp board somewhere.

I'm assuming thsts -41 and -8? Both should be negative

That's 3.3 watts from what appears to be a 1/2 watt resistor.

 

[Brownie Mix]

Look for solder bridges on the foil side of the board as well . . . easy to do when recapping.

will try this evening

 

[Brownie Mix]

try lifting one end of these resistors start with the 68 ohm one .. then if still high current draw do same for other channel . you could of course do resistance checks with the power off for both sides of each resistor to ground . View attachment 3713004

will try this evening. thanks