It means your M2x is normal. Nothing abnormal there. Enjoy music, sleep soundly, don't worry.
MJ knows!
@Craigl59 : I can personally attest to the nut/thread arrangement on the daughter boards loosening over time with heat cycles. My unsolicited advice is to follow to the letter 6L6's recipe of toothed lock washers for attachment (post #13 of this thread) as opposed to what look like flat washers in your pics (they could be belleville/wave washers you are using, IDK).
In the end I opted for the German sockets that have been mentioned in this thread a few times—after I had identified my favorite boards.
@Craigl59 : I can personally attest to the nut/thread arrangement on the daughter boards loosening over time with heat cycles. My unsolicited advice is to follow to the letter 6L6's recipe of toothed lock washers for attachment (post #13 of this thread) as opposed to what look like flat washers in your pics (they could be belleville/wave washers you are using, IDK).
In the end I opted for the German sockets that have been mentioned in this thread a few times—after I had identified my favorite boards.
MJ: Thanks for the advice and the suggestions -- will check out post 13 carefully and redo the daughterboard nuts.
Cannot, however, use the M2X. The left channel starts smoking.
Not sure what is the cause because all aspects of the board build have been triple checked. What seems to be happening is that the mosfets on this board are getting too hot and causing related parts to smoke.
Got any ideas? Thought I would reverse the Kevotherm pads today to see if the other side offered better heat reduction.
Again, the problem starts after about 2 minutes -- otherwise the board behaves and calibrates normally.
Cannot, however, use the M2X. The left channel starts smoking.
Not sure what is the cause because all aspects of the board build have been triple checked. What seems to be happening is that the mosfets on this board are getting too hot and causing related parts to smoke.
Got any ideas? Thought I would reverse the Kevotherm pads today to see if the other side offered better heat reduction.
Again, the problem starts after about 2 minutes -- otherwise the board behaves and calibrates normally.
If it works it is ok. If it doesn't work something is not right. Hard part when we build the stuff is finding the mistake. We "know" we did it right and the mistake becomes invisible to our eyes.
How does the current flowing through the hot mosfets compare to the side that works? Might lead you to the problem.
How does the current flowing through the hot mosfets compare to the side that works? Might lead you to the problem.
Is you bias on the “bad” channel constant or “running away” and causing the smoke?
Did you build the DBT, or do you have a Variac? That will help tremendously to power up and take voltages without burning up any parts.
Did you build the DBT, or do you have a Variac? That will help tremendously to power up and take voltages without burning up any parts.
Redid the standoffs for the DB with lock washers, removed the 2 to 4 short, and installed a new MountainView DB. Reversed the Keratherm insulators and put all back making sure everything was tight. Always check under the board to make sure there is plenty of space.
Started power, the LED light came on and the board looked normal until 1:44 in when faint smoke started appearing -- again around the large capacitor and IRFP9240 mosfet.
Signal Lost: Yes, agree that the hard part is finding out the problem. Here, I just cannot get the board right and have tried everything possible. Not sure I will have enough time to measure the mosfet before the smoke starts. Is it the center pin and ground that should be checked?
Thanks, all for your contributions. Have gotten to the point where I am reluctant to turn on the unit because of the constant smoking. Since the dual smps ACAs I have built are trouble free, and the PSU that PaulInWA helped with always work, having one channel work and the other always smoke is ruining my build experience. As always, suggestions are appreciated.
Think the tell-tale fact is that it takes 1:44 for the smoke to start. This suggests something is heating up and when it reaches a certain point, starts to smoke.
Started power, the LED light came on and the board looked normal until 1:44 in when faint smoke started appearing -- again around the large capacitor and IRFP9240 mosfet.
Signal Lost: Yes, agree that the hard part is finding out the problem. Here, I just cannot get the board right and have tried everything possible. Not sure I will have enough time to measure the mosfet before the smoke starts. Is it the center pin and ground that should be checked?
Thanks, all for your contributions. Have gotten to the point where I am reluctant to turn on the unit because of the constant smoking. Since the dual smps ACAs I have built are trouble free, and the PSU that PaulInWA helped with always work, having one channel work and the other always smoke is ruining my build experience. As always, suggestions are appreciated.
Think the tell-tale fact is that it takes 1:44 for the smoke to start. This suggests something is heating up and when it reaches a certain point, starts to smoke.
bullittstang: Measured the bias with 2 connected to 4 and the RCA shorted -- it stayed steady at about -0.05 vdc. Do not have a Variac and have limited electronic knowledge. Do have all of the calibration tools used for tape equipment, MV Meter, Scope, DC generator, and all but, again, have limited knowledge outside of calibration use. And yes, built all of the boards including a number of the MountainView ones.
What keeps me wondering is the fact that the right channel has always worked and caused no problems and I have, of course, used the same limited skill set on both boards. As noted above, have tried 2 left-channel boards and cannot get either to work. Am sure about the soldering connections as they have been triple checked. Had to substitute a different cap for C2 but it was rated at 10uf 50volt. It is a Nichicon Aluminum Electrolytic Radial Leaded at 20%.
What keeps me wondering is the fact that the right channel has always worked and caused no problems and I have, of course, used the same limited skill set on both boards. As noted above, have tried 2 left-channel boards and cannot get either to work. Am sure about the soldering connections as they have been triple checked. Had to substitute a different cap for C2 but it was rated at 10uf 50volt. It is a Nichicon Aluminum Electrolytic Radial Leaded at 20%.
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Craigl59 if you are turning on an amp with a known problem without several meters connected at various locations to measure voltages, how do you expect to find the problem? I'm not picking on you just asking what is your plan for finding the fault? Bullitstang keeps recommending a dim bulb tester because it will give you an indication of a problem or a Variac to bring the voltage up slowly while you check the voltages at each point possible. If you have one board working you can power only it up and make a list of the voltages at every point you can measure.
Only by employing a systematic trouble shooting plan are you going to find this fault. If you have one minute and 44 seconds til smoke you should be able to take a few voltages before hitting the kill switch. Do you have meter leads that clip on? I would be lost without them.
Only by employing a systematic trouble shooting plan are you going to find this fault. If you have one minute and 44 seconds til smoke you should be able to take a few voltages before hitting the kill switch. Do you have meter leads that clip on? I would be lost without them.
Signal Lost: OK, have a volt meter and a MV meter that can be connected -- both have clip on leads and, like you, use them a lot. What do I connect the meters to? To the center and ground pin of the IRFP9240 mosfet? And secondly to the incoming VPos and ground? Do not know the technique and cannot fathom the recommended voltages from the schematic on page 1.
Ok so this is where schools starts. Disconnect the trouble board and only power the working side. Print out a copy of the schematic. Connect black meter lead to chassis/ power supply ground and test every spot possible writing the voltages down on the schematic. When that is complete connect the meter across the output resistors R13 and R14( black on one lead, red on the other). One at a time and read the voltage. Apply Ohm's law to find the current through those resistors. Do not short anything with your leads. If things are close together it is better to turn off the amp and and move the meter probe and then power up. Now you will have enough information to find where the other board behaves different.
When you say the one board works, does that mean it plays music? Once I was thrown off by comparing two boards that were not working but in different ways. Let me know if this makes sense to you.
When you say the one board works, does that mean it plays music? Once I was thrown off by comparing two boards that were not working but in different ways. Let me know if this makes sense to you.
Both channels play music and the trouble, left channel played music before it blew the transformer -- almost 5 minutes worth.
Understand some of what you state (and thanks, of course) but am not sure about "every spot possible." What signifies "possible?" Will look up Ohm's law and see the specific formula.
When the first trouble board "blew" it was always one of the 0R47 that got fried. Both of these are being fed by the mosfets. Does that suggest mosfet failure?
Understand some of what you state (and thanks, of course) but am not sure about "every spot possible." What signifies "possible?" Will look up Ohm's law and see the specific formula.
When the first trouble board "blew" it was always one of the 0R47 that got fried. Both of these are being fed by the mosfets. Does that suggest mosfet failure?
This is where the DBT would help you because you are taking voltages with the unit on.
I would start at the mosfet, either one, with black probe on ground touch the red probe to each leg of Mosfet (gate, source and drain) - write down each voltage.
Next, take voltages on both sides of that 0.47r resistor you said is smoking. Then take voltage across that resistor (black probe one one leg and red probe on the opposite leg of the 0.47r resistor). Should be small number in mV, which tells us the current.
With these 5-6 voltages we can start figuring out the issue.
You can also take same voltages on working channel to compare - please share with us.
This might be enough to point you to the issue too.
I would start at the mosfet, either one, with black probe on ground touch the red probe to each leg of Mosfet (gate, source and drain) - write down each voltage.
Next, take voltages on both sides of that 0.47r resistor you said is smoking. Then take voltage across that resistor (black probe one one leg and red probe on the opposite leg of the 0.47r resistor). Should be small number in mV, which tells us the current.
With these 5-6 voltages we can start figuring out the issue.
You can also take same voltages on working channel to compare - please share with us.
This might be enough to point you to the issue too.
Well to take a measurement you must be able to connect your meter lead to the spot. So every place you can connect your meter.
If you try to guess at the problem if will be elusive. Mosfets usually fail shorted or open.
If you look at the schematic after the mosfets there is a loop of three resistors and three transistors. It is there for a purpose and it needs to be working correctly. Plus there are resistors and a pot on the other side of the mosfets that need to be working correctly. Two questions for you is this R13 or R14 and when you posted about three transformers but there is only one transformer on the board. Why three?
If you try to guess at the problem if will be elusive. Mosfets usually fail shorted or open.
If you look at the schematic after the mosfets there is a loop of three resistors and three transistors. It is there for a purpose and it needs to be working correctly. Plus there are resistors and a pot on the other side of the mosfets that need to be working correctly. Two questions for you is this R13 or R14 and when you posted about three transformers but there is only one transformer on the board. Why three?
bullittstang: superb response and I thank you. Need these kind of specifics as I am truly "flying blind." Will work on this over the weekend, getting my nerve up, and report as soon as I have some figures.
Another sign of the DIY site helping those of us with issues.
Another sign of the DIY site helping those of us with issues.
Feel free to connect your leads power on, count to 10, write the voltage and turn off, so you don’t run the risk of shorting your leads and causing more damage.
Voltages should stabilize very quickly after turn on at these points
Voltages should stabilize very quickly after turn on at these points
Signal Lost: Don't recall mentioning 3 transformers -- transistors, perhaps -- which post is this? Did replace 3 diodes and 3 transistors on the original trouble board.
To recap:
The first board had the mosfets switched and, when initially turned on, started blowing smoke at R12 and R11 -- both of these resistors and the 0R47 below them (R14) were blown. Replaced these and the 3 transistors, two mosfets, and cleaned all up, then tried it again.
This time it worked for 5 minutes, playing music, then blew the transformer. At this time, the other 0R47 (R13) was completely fried and produced burn marks on the board and a black spot that appears in the center portion of the board when held up to light.
SO, cleaned all this up, replaced the mosfets (again), diodes, resistors, transformer and large cap, and checked the soldering carefully.
When this was turned (last gasp for the first board) it started to smoke over RV1 (from below, probably IRFP240 or R13).
Then went to the new board, which was very carefully produced, and the problem with the smoke at 1:44 occurred -- probably from IRFP9240 (but up from the back of the board).
SO am going to try the measurements offered above and will let you know. Will take a bit as am very cautious with the board and unit now that it has bitten me so many times.
To recap:
The first board had the mosfets switched and, when initially turned on, started blowing smoke at R12 and R11 -- both of these resistors and the 0R47 below them (R14) were blown. Replaced these and the 3 transistors, two mosfets, and cleaned all up, then tried it again.
This time it worked for 5 minutes, playing music, then blew the transformer. At this time, the other 0R47 (R13) was completely fried and produced burn marks on the board and a black spot that appears in the center portion of the board when held up to light.
SO, cleaned all this up, replaced the mosfets (again), diodes, resistors, transformer and large cap, and checked the soldering carefully.
When this was turned (last gasp for the first board) it started to smoke over RV1 (from below, probably IRFP240 or R13).
Then went to the new board, which was very carefully produced, and the problem with the smoke at 1:44 occurred -- probably from IRFP9240 (but up from the back of the board).
SO am going to try the measurements offered above and will let you know. Will take a bit as am very cautious with the board and unit now that it has bitten me so many times.
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At this point, I would probably start with a brand new PCB and a fresh set of components. Probably the fastest way to get a working amp.
Later on the defective board can be debugged as a learning exercise, or not.
Later on the defective board can be debugged as a learning exercise, or not.
A lot of smoke can be prevented using vario-trafo (with A-meter), Lab-supply with current limiter. Using rail-fuses can also be a good idea.