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September 18, 2020, 04:16:57 AM

Author Topic: 1 LED lights up immediately after turning it on, smoke from one of the 270ohm 5w  (Read 1283 times)

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Offline Jimb0

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Getting some issues with my build. The D2 LED on the right high current c4s board lights up immediately when I turn it on. After a few moments the 270ohm 5 w resistor on the right side started smoking. I turned it off immediately after that.

Picture 2 shows the smoking resistor
Picture 4 shows the LED that lights up (the top right D2 is the one that lights up first)

« Last Edit: August 19, 2019, 09:18:50 PM by Jimb0 »

Offline Jimb0

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Offline Jimb0

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Offline Paul Birkeland

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I would remove the wire going to IA on the right high current C4S board, then test the left channel of the amp to be sure everything fires up as it's supposed to.

To get behavior like that, there has to be a miswire or an improperly placed component on the high current C4S board, as the current drawn certainly does not appear to be regulated!
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Jimb0

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Do I need to replace the 270ohm 5w resistor?

Offline Paul Birkeland

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Does it still measure as 270 ohms?
Paul "PB" Birkeland

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Offline Jimb0

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It's reading 245 now

Offline Jimb0

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I see my mistake. I switched the MJE5731A and the TIP-50's. I wasn't paying attention to this when I was soldering the parts because I assumed they were the same. Lesson learned  :D

Offline Paul Birkeland

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I'm glad you caught this.  I would plan on throwing away the transistors that you have now and replace them with new ones.  A new PN2907 and 2N2222 would probably be a good idea as well on that board.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Jimb0

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Hi Paul. I'm still waiting on the PN2907A and the 2N2222's but I tested it with the new 270 ohm resistor. I'm getting 0v on IA of the low current and high current c4s on the right side now. Only the left high current c4s I'm getting voltages of ~200 at IA

Is this due to those two components needing replacement?

Offline Paul Birkeland

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I would not have fired it up without replacing all of the transistors.  You may now need another new TIP50 and MJE5731A.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Jimb0

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Yikes, ok no problem

Offline Jimb0

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Hi Paul. Ok so I replaced all the transistors on the right high current c4s board and I'm getting these readings. All the voltages on the left board are ok. At the center Low Current C4S board I'm getting no voltage on OB and no voltage on the A side.

Right High Current C4S
IA 211v
OA 0v
bA 0v

IB 0v
OB 0
bB 0


Low Current C4S
IA 0v
OA 0v
KregA 1v
bRegA 0v


IB 150v
OB 0v
KregB 5v
bRegB 150v

Offline Paul Birkeland

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Nothing is coming out of the OA side, or it could be getting shorted to ground. 

You can remove the red jumper on the bottom side of that board to take the B side C4S out of the equation, then see if the voltage at OA pops up.  It would be OK to just remove the end that's at OA. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Jimb0

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Still nothing at OA after removing the red jumper