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Post by mastertech on Jan 16, 2023 18:37:43 GMT -5
Can you test and see if there is any DC on R5031, either side? Then compare to R5030.
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Post by serafis on Jan 16, 2023 22:24:25 GMT -5
Can you test and see if there is any DC on R5031, either side? Then compare to R5030. Yes there is less than -25mV on one side of R5030, and -40mV on the other side. On R5031, there's around -200mv on one side and -240mv on the other. So definitely DC offset on R5031 (right channel). |
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Post by mastertech on Jan 17, 2023 11:56:28 GMT -5
I keep looking at D5001 with curiosity. Do you have a replacement for that diode and if not, could you swap it with D5000 maybe?
I'm assuming you have already changed out C5021?
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Post by serafis on Jan 17, 2023 19:38:59 GMT -5
I keep looking at D5001 with curiosity. Do you have a replacement for that diode and if not, could you swap it with D5000 maybe? I'm assuming you have already changed out C5021? D5000/1 are tiny SMDs - I very carefully swapped them - no difference, the hiss is still on the right channel. And yes, I'd already swapped out C5021 (but not R5101 as I'm a bit nervous around tiny smds with my aging hands and eyes!) |
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Post by mastertech on Jan 17, 2023 21:19:05 GMT -5
If possible I would like to see the DC voltage reading of B,C and E of Q5031 and Q5041.
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Post by serafis on Jan 17, 2023 22:50:46 GMT -5
If possible I would like to see the DC voltage reading of B,C and E of Q5031 and Q5041. Ok, I've done this (with comparison with Q5030 and Q5040) Q5031: B=22.6V, C=0.4V, E=23.3V Q5030: B=23.1V, C=1.1V, E=23.8V Q5041: B=22.2V, C=1.8V, E=22.9V Q5040: B=23.0V, C=1.1V, E=23.7V There are some discrepancies between Q5030/C (1.1V) and Q5031/C (0.4V); and between Q5040/C (1.1V) and Q5041/C (1.8V) |
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Post by mastertech on Jan 18, 2023 11:54:17 GMT -5
I am assuming your voltages for Q5040 and Q5041 are "-" (minus) voltages?
Can you get me voltages of both sides of R5181 and R5191? And other channel.
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Post by serafis on Jan 18, 2023 15:08:14 GMT -5
Yes, my bad, voltages on Q5040 and Q5041 are negative. Also, need to backtrack a bit as I was measuring voltages to chassis ground, and only just realised that U0030 actually needs to be screwed down to the main board to ground it to the chassis. So here are the revised readings:
Q5031: B=52.24V, C=0.50.4V, E=52.72V
Q5030: B=-51.91V, C=-1.67V, E=-52.62V
Q5041: B=52.78V, C=1.11V, E=53.36V
Q5040: B=-52.77V, C=-1.04VV, E=-53.25V
Measuring the resistors, Right and Left legs (as on the schematic), the voltages do fluctuate by several mV, trending downwards, as the AVR 'warms up':
R5181 R=55.51V, L=55.45V
R5180 R=55.56V, L=55.37V
R5191 R=-55.37V, L=-55.34V
R4190 R=-55.52V, L=-55.37V
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Post by mastertech on Jan 18, 2023 18:07:54 GMT -5
Could you please clarify your Q5031 collector reading.
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Post by serafis on Jan 18, 2023 18:28:17 GMT -5
Sorry, typo, Q5031: C=0.50V
Q5031 collector seems low and Q5030 collector seems high, when compared with the other channel.
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Post by tjmotter on Jan 18, 2023 21:49:29 GMT -5
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Post by serafis on Jan 18, 2023 22:32:15 GMT -5
Thanks Todd, I'm guessing it will turn out to be one of the surface mounted transistors, as there's not much else on this board that I haven't replaced or swapped with a good channel! I don't currently have replacements for any of these and am a bit reluctant to try swapping them due to the possibility of heat-damaging the board or the transistors in the process. Plus if I do identify the culprit, I don't have a replacement for it and they're hard to source in small quantities, especially in New Zealand. But I may summon up the courage to do this when all other avenues are exhausted.
Thanks for the tip about QuikChip - seem to recall Dave from eevblog demoing it in a video and I was quite impressed.
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Post by mastertech on Jan 19, 2023 11:47:03 GMT -5
I agree, it is probably time to start changing out some of these parts. We mostly have it narrowed down to the same location that Todd mentions so I would think it would be the place to go next.
I also agree with the QuickChip. I have also been using it since it first came out. Before that it was using a wide iron or 2 irons or cutting off legs and removing individually. QuickChip made it a lot easier.
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Post by serafis on Jan 19, 2023 14:24:23 GMT -5
OK, I'll need to send off for some QuickChip and for the smd transistors as I can't get these in NZ for a reasonable cost or quantity. May take a few weeks. Thanks for the help so far and I'll post back once I have the items I need for the next steps (and hopefully success!)
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Post by tjmotter on Jan 19, 2023 14:34:04 GMT -5
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