AudioCircle
Industry Circles => Bryston Limited => Topic started by: ambrosia on 10 Sep 2020, 07:45 am
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Hi,
I have a 3B-ST that I purchased new - not sure of the year, but more than 20 years ago.
I shorted the outputs about 10 years ago and Bryston kindly sent me replacement output transitors which got me going again. The unit has been sitting in a box for the last 8 years or so, and I honestly can't remember if it was working when I packed it away. Anyway, I thought I'd start using it again, plugged it in and it was dead. Had a peek inside and found the top the LM317 regulator floating around in the case. Further inspection shows that it had, indeed blown it's top. Also, I found a defective zener (z5/1N4741) and cap (2U2 tantalum/C23) which makes sense - this would short the output of the LM317.
Luckily I have a bunch of LM317 and will order some caps and zeners. However, a post that I found on DIYAudio had the exact same problem. When the poster emailed Bryston, they said they were no longer using tantalum caps, but he doesn't say what was recommended as a replacement.
The power power supply board is marked 3BST-PSB 4.8 JUL 96, with a hand written date of 4/28/97. It's 230 V.
I have attached a schematic (V5.0) from the Bryston website, and I've marked the defective components. However, I can't see the MJE172 tranny (T4 and T10), on my board plus a few other things are different.
Wondering if anybody can help with the tantalum replacement and a better schematic.
Leigh
(https://www.audiocircle.com/image.php?id=214380)
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Is NRB different than the ST?
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Klik. (https://www.hififreak.nl/wp-content/uploads/2020/01/3B_4B_5B_7B_8B_9B_14B_SCHEMATICS-1.pdf)