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Wayne's BA 2018 linestage
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Old Yesterday, 01:38 PM   #2631
PJN is offline PJN  United States
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Try carefully reflowing your jfets. I had a similar problem on one of my builds and it turned out to be a bad joint on one of those little buggers.
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Old Yesterday, 04:32 PM   #2632
andynor is offline andynor  Norway
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Quote:
Originally Posted by bpr View Post
Photo of the wonky channel is attached. I will figure out how to do a diode mode test, and report back with what I find out.

Thanks.
I’d do exactly as Choky and PJN prescribed. And focus my beep test to the cold-looking joints of Q21 and Q24. Reflow with liquid flux is preferred, as grease might make contact between legs if it gets under the transistor (tight space, difficult to clean). Careful when reflowing, they aren’t too happy with high temps and multiple reheats, imoe.
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Old Yesterday, 04:34 PM   #2633
bpr is offline bpr
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Originally Posted by Zen Mod View Post

for now - use buzzer terst position(it beeps for everything under 30 to 50 ohms, depending on meter production) - that's tool for checking continuity

say -- one probe on tiny leg of JFet, other probe to resistor pin on same trace

if you hear buzz, JFet pin is (hopefully) properly soldered
Quote:
Originally Posted by PJN View Post
Try carefully reflowing your jfets. I had a similar problem on one of my builds and it turned out to be a bad joint on one of those little buggers.
Checked the JFETs and the continuity was bad on Q21, which seems to make sense based on the issues I've been having. I will remove, clean and reflow that one and see if it fixes the problem. All of the others seem to be working properly. Thanks again for the guidance. I'll report back with results.

Last edited by bpr; Yesterday at 04:41 PM.
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Old Yesterday, 04:47 PM   #2634
andynor is offline andynor  Norway
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Hi, nice to see you got some results!

I’d be hesitant in removing the JFET. I recommend you just reflow for starters. They are easy to break, and hard to pull without destroying them.

Also, be careful with pliers close to the pcb if you choose to remove it. If you scratch the PCB, you could have issues with stability if copper gets in contact with for example flux residue etc.
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Old Yesterday, 05:06 PM   #2635
avdesignguru is offline avdesignguru  United States
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A flux pen helps with reflow of SMD components (also initial installation):
https://amazon.com/gp/product/B07B53LNGX
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Old Yesterday, 06:06 PM   #2636
Russellc is offline Russellc  United States
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Wayne's BA 2018 linestage
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Originally Posted by PJN View Post
Try carefully reflowing your jfets. I had a similar problem on one of my builds and it turned out to be a bad joint on one of those little buggers.
My first one cleared up once I scrubbed the tiny jfet pads with iso and tooth brush.

Russellc
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Old Yesterday, 11:38 PM   #2637
bpr is offline bpr
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I checked and reflowed the jfets which solved a number of issues. I can now adjust dc offset on the output of that channel via P1, and all but two of the resistor measurements between channels are the same. The only two that are still off are R40 and R43. Does that mean it's a Q21 issue, like maybe the jfet is bad? Good idea to replace and measure again?
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