Right 🙂 but our theory won't fail us... there is something simple at the bottom of this.
Check by measurement (we don't assume anything now so forget the circuit reference numbers and board markings) that the 6k8 resistor with plus 74 volts on it is the one that goes directly to pin 8 of the opamp (so measure the continuity). Do the same for the resistor with a measured negative 74 volts on it. Make sure that goes to pin 4.
Recheck again (not going off board markings of reference numbers) that the appropriate Zener orientation matches its connection to the correct 6k8.
The switching part refers to the power supply and its triac control, the amp is 100% conventional Class AB
I found in my miscellaneous simulations one of the Carver that I put together a year or two back. This shows the circuit much more clearly than the printed manual and you can see that there is nothing that could kill those rails besides the opamp, the Zeners and the caps. The big big clue to me is the -/+0.6 volts you see as that just screams out that the Zener orientation is incorrect somewhere along the line. So at this point do not assume any board markings and component reference numbers are actually correct. Prove they are by actual measurement of voltage and continuity.
I'll give it a go, but I've already done that and measured out the same -0.37v on both of the pins; exactly the same as what is coming off R182/183. I didn't check those 15k resistors yet but, for both of them to be bad.... this doesn't make any sense.
It won't be those. Even if they were wire links they would only load the supply via the B/E junctions of Q101 and Q103 and their 1k5 emitter resistors. The -/+15 volts would be down but not at the levels you have.
I think its something much more fundamental than that,
When I have fixed other people's problems, invariably it was something simple they are certain they have checked.
Ok! I made progress. I did have a solder bridge between 2 resistors. Stupid rookie mistake; must have happened when I was re-flowing the cold joints. So, now I have 16v +/- at IC101, which is because I installed 16v zeners as a test. I'll put the 14s back in. But I ran into another problem. the right channel is causing the amp to go into protection and the heatsink and transistors are very hot. Left channel is fine, and it works with just the left channel with no issue. It's not a speaker or load issue, because it cuts into protection as soon as there is any input volume going into the right channel.
Voltages look correct between both channels at the output transistors.
Voltages look correct between both channels at the output transistors.
Good progress on clearing the short!
Are you saying with no volume applied, the protection doesn't activate? Heat sinks still hot in same circumstances?
With input shorted, would you report voltages on right channel opamp, pins 5,6,7 and at amp output where convenient in front of output relay, eg. at the junction of the emitter resistors R170, R172, etc. I think these voltages will get us started.
Are you saying with no volume applied, the protection doesn't activate? Heat sinks still hot in same circumstances?
With input shorted, would you report voltages on right channel opamp, pins 5,6,7 and at amp output where convenient in front of output relay, eg. at the junction of the emitter resistors R170, R172, etc. I think these voltages will get us started.
Well, actually now I have no relay 😒
I have no idea what happened. 150w / 200w dim bulb showing no short on power up, but I've heard some of these amps don't like dim bulbs.... I plugged into mains and get the same thing.
I have no idea what happened. 150w / 200w dim bulb showing no short on power up, but I've heard some of these amps don't like dim bulbs.... I plugged into mains and get the same thing.
Yeah, I think I lost my power supply... not getting what I'm supposed to at the filter caps... damn. I'm getting less than a volt at the filter caps. Something was clearly on its way out.
Edit: I think I'm about to give up on this. I pulled the supply off the main board to check voltages without the main board loading anything down, and I smoked R176 on the main board. No explanation. Tested again, and watched a trace nearby catch fire! Now I'm blowing fuses. I don't know what happened in the last hour but I'm at a loss now.
Edit: I think I'm about to give up on this. I pulled the supply off the main board to check voltages without the main board loading anything down, and I smoked R176 on the main board. No explanation. Tested again, and watched a trace nearby catch fire! Now I'm blowing fuses. I don't know what happened in the last hour but I'm at a loss now.
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This is one of the cases where the bulb limiter does NOT work. Unless the power supply gets full voltage, through a low impedance source, it will misbehave.
And one fried component will usually cause a cascade chain reaction. When fixing one of the “cubes” I ended running the amp off a conventional (but 3 tier) external supply - on a bulb limiter - until the power amp section was working properly. And then checking every single component in the power supply, one by one, out of circuit until I rooted out the bad resistors that were either the cause or the result of the triac failure. And the caps that the failure also destroyed when the output voltage shot up. 25 volt caps on the 25V rail, and a pair of 25V caps in series on the 50 volt. Not smart to begin with…. They got up-rated.
And one fried component will usually cause a cascade chain reaction. When fixing one of the “cubes” I ended running the amp off a conventional (but 3 tier) external supply - on a bulb limiter - until the power amp section was working properly. And then checking every single component in the power supply, one by one, out of circuit until I rooted out the bad resistors that were either the cause or the result of the triac failure. And the caps that the failure also destroyed when the output voltage shot up. 25 volt caps on the 25V rail, and a pair of 25V caps in series on the 50 volt. Not smart to begin with…. They got up-rated.