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)?
Coming back to this thread to wrap up my soft start circuit research. I had pulled 5 non-working amps from the "To Be Recycled" shelf at a facility that was moving and had to empty their store room quickly. Three Brystons 4B, 4Be, 4B-NPB, and two Haflers 9505 & DH-220. I repaired the Haflers (replaced one of the big capacitors, and two power switches) and started on the Brystons.
The 4Be and 4B-NPB are early editions of the NRB model. Apparently the soft start boards were a work in progress because when I bypassed the SSBs and brought the amps up to power with a variac both amps worked. (One channel didn't work but it was just a bad Mono/Stereo switch). I spent quite a few hours and parts trying to repair the SSBs but they seem fairly complex circuits for my limited ability and I had no luck. In my research I had read about Bryston build quality and legendary customer service. Both are true. I called them and they said they could build new SSBs for $100 each. They arrived in two weeks with free shipping. They sent the SST version saying it is compatible with the NRB models. It is indeed and the amps work now.
One quirk with the SSBs: I had to transfer the original power LED to the new boards. The circuit trace of the powering wires on the new boards didn't connect to the LED solder pads so the LED didn't light. This took some time to figure out since a bad trace is the last thing one would check for in a Bryston, especially with their (pita) double-sided soldering. I tacked the wires directly to the LED and all good now. Not very elegant but good enough for my shop stereo.
The third amp, a 4B from the 80s, does not have the same build quality as the NRBs and can't be as easily disassembled for repair (also has square transformers not the nice toroidals). A few output transistors were shorted so I'm saving that one for parts as I seem to have no immediate need for another nice amplifier.
3 free Brystons on the bench at the same time
The 4Be and 4B-NPB are early editions of the NRB model. Apparently the soft start boards were a work in progress because when I bypassed the SSBs and brought the amps up to power with a variac both amps worked. (One channel didn't work but it was just a bad Mono/Stereo switch). I spent quite a few hours and parts trying to repair the SSBs but they seem fairly complex circuits for my limited ability and I had no luck. In my research I had read about Bryston build quality and legendary customer service. Both are true. I called them and they said they could build new SSBs for $100 each. They arrived in two weeks with free shipping. They sent the SST version saying it is compatible with the NRB models. It is indeed and the amps work now.
One quirk with the SSBs: I had to transfer the original power LED to the new boards. The circuit trace of the powering wires on the new boards didn't connect to the LED solder pads so the LED didn't light. This took some time to figure out since a bad trace is the last thing one would check for in a Bryston, especially with their (pita) double-sided soldering. I tacked the wires directly to the LED and all good now. Not very elegant but good enough for my shop stereo.
The third amp, a 4B from the 80s, does not have the same build quality as the NRBs and can't be as easily disassembled for repair (also has square transformers not the nice toroidals). A few output transistors were shorted so I'm saving that one for parts as I seem to have no immediate need for another nice amplifier.
3 free Brystons on the bench at the same time
Nice!
I'd rather the E-I transformers to be honest. The early 4B amps were not nice, a pain to work on. The earlier ones than yours had a bias control issue on top of everything else.
I'd rather the E-I transformers to be honest. The early 4B amps were not nice, a pain to work on. The earlier ones than yours had a bias control issue on top of everything else.
For sure it's the soft start circuit and the IC is the phase control that likely goes bad. you can power the transformer up bypassing the soft start triac using a variac and confirm if everything will start up normally then troubleshoot the soft start circuit. I would pull both amp modules out and check the supply voltages then discharge the supply voltages and test each channel. Bryston amps probably the most easiest to work on since they are modularly built for field serviceable and swappable.