anatech said:
That could be. I did a similar circuit with a standby relay that shorted the output stage gates to the output lines, killing the bias voltage along with any drive signal present.
A defect in the bias circuit here could cause the outputs to draw several amps continuously, which might account for the initial blown rectifiers and the continued DC fuse blowing. Another thing that might cause this is a short in either or both coupling capacitors.
I wonder why the DC fuses didn't protect the rectifiers from blowing up in the first place. Perhaps the original fuses were replaced by units with too high a rating?
Thanks Chris,
I thought the parts that blew in this case were bridge rectifiers, not gain devices. You can just make out one of these in the brochure interior photo of the VK200, mounted on the amp board and possibly (not too sure about this) attached to the heat sink.
They don't look like the biggest such packages available, but are maybe the next size down, which IIRC have surge current ratings in the 200A range. Sorry not to have better info - the brochure picture is as close to an actual VK200 circuit board as I've gotten.
Of course, something *else* could have blown at the same time, and maybe that's what you were thinking. Along those lines, I recall having a conversation with Victor about this circuit several years ago in which he said that they used a crowbar (triac, I assume) to protect the output from severe DC offset. If so, that would certainly be something to watch for.
I thought the parts that blew in this case were bridge rectifiers, not gain devices. You can just make out one of these in the brochure interior photo of the VK200, mounted on the amp board and possibly (not too sure about this) attached to the heat sink.
They don't look like the biggest such packages available, but are maybe the next size down, which IIRC have surge current ratings in the 200A range. Sorry not to have better info - the brochure picture is as close to an actual VK200 circuit board as I've gotten.
Of course, something *else* could have blown at the same time, and maybe that's what you were thinking. Along those lines, I recall having a conversation with Victor about this circuit several years ago in which he said that they used a crowbar (triac, I assume) to protect the output from severe DC offset. If so, that would certainly be something to watch for.
Hi Joe,
I was just inferring that from the course of the conversation here. If this has a triac protected output you have just explained the fuse blowing I think.
ben goh,
If this is the case, you need a variac and either short the triac gate to common, or disconnect the main terminal from the amplifier output. I like the disconnection option as the triac may fail short or funky leaky.
After that is done you can begin to troubleshoot your problem. I have zero information on this amplifier. Just going on what I've seen over the years.
-Chris
I was just inferring that from the course of the conversation here. If this has a triac protected output you have just explained the fuse blowing I think.
ben goh,
If this is the case, you need a variac and either short the triac gate to common, or disconnect the main terminal from the amplifier output. I like the disconnection option as the triac may fail short or funky leaky.
After that is done you can begin to troubleshoot your problem. I have zero information on this amplifier. Just going on what I've seen over the years.
-Chris
Hi Anatech
Sad to say that no triac is found on the circuit except for two
opto-coupler PS2502-2 and I have replaced that too.
There are three supplies feeding one channel, two voltages of
+58 volts feeding the output mosfets, couldn't determine the
third voltage.
Will try the relay first.
Thanks
Sad to say that no triac is found on the circuit except for two
opto-coupler PS2502-2 and I have replaced that too.
There are three supplies feeding one channel, two voltages of
+58 volts feeding the output mosfets, couldn't determine the
third voltage.
Will try the relay first.
Thanks
The triac was an assumption on my part - I think this is usually what is meant by "crowbar" - but it could be something else.
Are the two optocouplers wired across the output terminals via a pair of series resistors and a bypass cap? If so, they may be part of a DC offset sensing system. The "crowbar" in that case might be the standby relay itself.
Are the two optocouplers wired across the output terminals via a pair of series resistors and a bypass cap? If so, they may be part of a DC offset sensing system. The "crowbar" in that case might be the standby relay itself.
Hi lgreen,
Thanks. I've never heard one. Hot seems to equal high end these days.
Hi Joe,
I've only ever seen a triac used to crowbar audio outputs. Relay contacts and the flex wire is not reliable enough. Besides, a triac fails short and that's what you would want (strangely enough).
A picture of the circuit board may give a clue as to the circuit arrangement, or not. A schematic is really what we need here.
-Chris
Thanks. I've never heard one. Hot seems to equal high end these days.
Hi Joe,
I've only ever seen a triac used to crowbar audio outputs. Relay contacts and the flex wire is not reliable enough. Besides, a triac fails short and that's what you would want (strangely enough).
A picture of the circuit board may give a clue as to the circuit arrangement, or not. A schematic is really what we need here.
-Chris
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.