Sound Skulptor forums
Build help and troubleshooting => AB528 Microphone preamplifier => Topic started by: Alaska on September 21, 2024, 05:09:16 AM
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Hello. I was saddened to smell burning on first firing up my ab528. I’ve built many 500 series and felt confident I understood and completed every step correctly. The power was only on about 10 seconds and I see that r33 and r34 surely burned with possible discoloration on d7. There is also a little melting on j2b. The power Led never lit up.
Every capacitor has correct polarity and magnifying glass couldn’t find any bridged solder spots or issues. Please help!
(https://i.imgur.com/mrYtA0K.jpeg)
(https://i.imgur.com/f7hXrOR.jpeg)
(https://i.imgur.com/rQ4cFjM.jpeg)
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Check that the power transistors Q5, Q6 are not swapped.
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I checked and -91 is in q5, where it should be. Next?
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Ive replaced r33 and r34. What should I check before trying to power up again?
I used my cranborne 500r8 before but think i will try my Lindell 510 500 rack this time as as the 500r8 is much more valuable.
Could I rig up a 9 or 12v underpowered power supply from a wall wart just for testing point purposes before inserting into 500 rack?
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Oh. Found something wrong. Diodes on di board are not correct 🙄
(https://i.imgur.com/QLATNoH.jpeg)
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Final update: fixed
The di board diodes got me. Oh well. Works now and sounds pretty darn good. Di on bass sounds fantastic. Mic pre is nice. Saturation on line level signal is not as good as i had hoped for processing tracks, but mic level and di is the main intended use. 🍻
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Well done!
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