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tdmckellar  
#1 Posted : Friday, July 14, 2017 5:26:28 PM(UTC)
tdmckellar

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I have been building the Placid HD and HD Bipolar, the HD I have successfully tested powered up and adjusted the voltage and current following the Placid HD v2.1 Guide (very helpful!)

However, after following the same steps for the HD BP, I got smoke from the resistors R1 (A and B) and R2 (A and B). I immediately powered off, but I am not sure what the issue is. I have checked solder joints which appear to be okay, and the polarity of the capacitors is correct. I did put some heatshrink (may have been adhesive backed) over QN5/QN3 and QP3/QP5 after I had read this could be beneficial. Could this be the issue? Could anyone advise how to proceed to troubleshoot?

Thank you.

Edited by user Friday, July 14, 2017 5:30:30 PM(UTC)  | Reason: Not specified

Brian Donegan  
#2 Posted : Friday, July 14, 2017 8:50:03 PM(UTC)
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This is almost always transposed transistors.

Use the parts list and check all the transistors are installed in the correct positions.
thanks 1 user thanked Brian Donegan for this useful post.
tdmckellar on 7/16/2017(UTC)
tdmckellar  
#3 Posted : Friday, July 14, 2017 9:05:57 PM(UTC)
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Thank you for your reply, could it have been caused by swapping QN3/QN5 and QP3/QP5? Also as a result, may I have damaged resistors R1 and R2?
Brian Donegan  
#4 Posted : Friday, July 14, 2017 9:28:59 PM(UTC)
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Yes. Any QP/QN swap will cause problems. The resistors are amazingly resilient, so they may be okay. It's entirely possible that all comps are okay, and swapping will fix it.
tdmckellar  
#5 Posted : Saturday, July 15, 2017 11:13:03 AM(UTC)
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I appear to have swapped QP1 and QN2 (swapping MJF122G with MJF127G). I tried to desolder and salvage the components but they had to be cut off. I should be able to get some new ones next week. I will install and retest asap and let you know the results. Thank you for your help.
Narukas  
#6 Posted : Wednesday, February 26, 2020 11:00:04 PM(UTC)
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Got into the same smoke situation - assembled Placid HD BP v2.1 with MJF122G and MJF127G wrong way around.
Replaced QP1,2, QN1,2 and R1A,B R2A,B resistors and all is well

Edited by user Sunday, March 15, 2020 10:19:15 PM(UTC)  | Reason: Not specified

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