First time poster. Thanks in advance for any help.
I have a Bryston 4Be with no AC at the input to the transformers. There's AC at the internal fuses and the thermal breakers are good. On the schematic I see a module in the neutral side of the AC circuit. Neutral is the bottom line. Hot is both fuses.
What is the purpose of the circuit? Current limiting maybe? Are triacs a common failure item. Would you suspect the optocoupler or the triac?
TDA1085 is a triac controller
MDC 3022 is an opto-triac
MAC 3020-25 is a high current triac.
I have a Bryston 4Be with no AC at the input to the transformers. There's AC at the internal fuses and the thermal breakers are good. On the schematic I see a module in the neutral side of the AC circuit. Neutral is the bottom line. Hot is both fuses.
What is the purpose of the circuit? Current limiting maybe? Are triacs a common failure item. Would you suspect the optocoupler or the triac?
TDA1085 is a triac controller
MDC 3022 is an opto-triac
MAC 3020-25 is a high current triac.
Attachments
A bit hard to confirm with the zoomed in schematic, but at first thought though, maybe a soft-start circuit? The portion I can see is similar to the SST soft start circuit....
Thanks. I attached the complete schematic. A search for Bryston soft start turned up this:
Those clever devils at Canadian high-end amplifier company Bryston, implemented soft start using a Triac and PWM. But, here's the clever piece, they piggy-backed upon the hard work done at Motorola (now ON Semiconductor), soft-starting big enormous electric motors. Yes, Bryston really did install a triac in their model 875 power amp, in series between the AC mains and the transformer primary. Yes they really did control the triac using a dedicated, special purpose motor controller IC called TDA1085C. https://www.diyaudio.com/community/threads/yet-another-soft-start-circuit.339117/post-6260970
Those clever devils at Canadian high-end amplifier company Bryston, implemented soft start using a Triac and PWM. But, here's the clever piece, they piggy-backed upon the hard work done at Motorola (now ON Semiconductor), soft-starting big enormous electric motors. Yes, Bryston really did install a triac in their model 875 power amp, in series between the AC mains and the transformer primary. Yes they really did control the triac using a dedicated, special purpose motor controller IC called TDA1085C. https://www.diyaudio.com/community/threads/yet-another-soft-start-circuit.339117/post-6260970
Well, there you go! It's a soft start circuit. If your not getting AC to the transformer, something in that circuit may have died. Check you're getting the correct voltage on the little zener regulator, look for the pulses at the output of the TDA chip, make sure they're getting past the optocoupler to the triac.
I have a Bryston 4Be with an issue (not my amp). When it is turned on, and volume is down all the way, both indicator lights on the front of the amp are green and the amp appears to be functioning correctly. When you turn the volume up the left light goes red (with no sound from left speaker). The right light remains green, but there is very slight sound coming from the right speaker. Anyone have any suggestions (it is out of warrany)?