Bryston 3B-ST repair

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ambrosia

  • Jr. Member
  • Posts: 4
Bryston 3B-ST repair
« on: 10 Sep 2020, 07:45 am »
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




pochago

  • Jr. Member
  • Posts: 5
Re: Bryston 3B-ST repair
« Reply #1 on: 21 Sep 2020, 01:55 am »
Is NRB different than the ST?

Hififreak

  • Jr. Member
  • Posts: 147
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Re: Bryston 3B-ST repair
« Reply #2 on: 23 Sep 2020, 06:00 am »