Signal Lost: Out of the 4 boards so far, two Channel As and one Channel B are affected by the low ohm problem. One Channel B works. You mentioned that you had the cards but hadn't yet built. Suggest you try the test described above before plunging on the transformers and such.
I have the transformers already. I just tested both my boards with 221 ohm at R11 and 150 ohms at R9 and R12. Both boards read 371 at pin 2 of Q5. Those were the only parts mounted and i measured from R14 to Q5 pin 2. 150 ohms was the reading at pin 3 of Q7.
However there are many other pathways involved with those resistors and I believe that you are looking at the wrong parts. Seems too much of a coincidence that the other resistor in that loop is R10 @ 100 ohms. Exactly the amount of resistance that is "missing". Plus the resistors on the base of the mosfets are 100 ohms. On the non-working boards something is not conducting when it should or conducting when it should not.
What resistance value do you get from R10 to pin 2 of Q5? What is that value on the working board.
So I am back to my advice of test everything. Start with continuity, check resistors, check the mosfets check the diodes. It is there. Wish I could be more help with Q6 and Q7 but I don't have any knowledge about those devices.
However there are many other pathways involved with those resistors and I believe that you are looking at the wrong parts. Seems too much of a coincidence that the other resistor in that loop is R10 @ 100 ohms. Exactly the amount of resistance that is "missing". Plus the resistors on the base of the mosfets are 100 ohms. On the non-working boards something is not conducting when it should or conducting when it should not.
What resistance value do you get from R10 to pin 2 of Q5? What is that value on the working board.
So I am back to my advice of test everything. Start with continuity, check resistors, check the mosfets check the diodes. It is there. Wish I could be more help with Q6 and Q7 but I don't have any knowledge about those devices.
As I was typing the above I got an idea. So I installed the resistors like above added two 0.47 ohms at R13 and R14 and a 150 Ohms at R8. Then I shorted pins 2and3 of Q6 and Q7. Measured from R14 to Q5 pin two and guess what. 221 ohms.
Signal Lost: Bet your board doesn't work. And if you take the shorts off does the R change?
Now your idea of R10 to Pin 2 is excellent. Here's what I got on the 3 non-working boards: 220R BUT 220 from either side of the 100R R10. How can this be?
Then checked the working board and it was 323 from the direct side to Pin 2 and 423 from the 100R side. So that makes sense. But the other 3 do not.
Great idea, SL! And got your suggestions about continuity and all and have been using them as noted above. Will remember them in the future (so no need to remind me yet again...LOL).
Now your idea of R10 to Pin 2 is excellent. Here's what I got on the 3 non-working boards: 220R BUT 220 from either side of the 100R R10. How can this be?
Then checked the working board and it was 323 from the direct side to Pin 2 and 423 from the 100R side. So that makes sense. But the other 3 do not.
Great idea, SL! And got your suggestions about continuity and all and have been using them as noted above. Will remember them in the future (so no need to remind me yet again...LOL).
because I had it. Nothing was soldered and I do not have the rest of the parts. But It would work.
I think it is called the Thevevin equivalent value. Represents what voltage would "see" as resistance looking in that direction of the circuit.
Now can you check to see if the mosfets are shorted or open. That would create a similar pathway as shorted Q6 and Q7.
I think it is called the Thevevin equivalent value. Represents what voltage would "see" as resistance looking in that direction of the circuit.
Now can you check to see if the mosfets are shorted or open. That would create a similar pathway as shorted Q6 and Q7.
A simple plan would be to swap Q6 and Q 7 from a non working board to the working board and test it. That would rule them out or indicate them as the problem.
I used 150 ohms because the 221 ohm resistor was in the same bag with them. They were left over fro building the H2. They key is that shorting Q6 and Q7 removed all but the 221 ohm resistor from the measurement at Q5 pin 2. This indicates that it is a component problem not a board problem.
Is that plan really the best? Unsoldering/desoldering overheating the parts...you may end up frying more parts in the process and make no progress.
Better leave the working board alone, buy a couple bucks worth of parts and do it right.
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I agree. Could be wrong component somewhere, wrong direction of component, damaged component, or soldering issue.
You've never once specifically mentioned (that I can find) measuring the precise points I mention on the board. Additionally, you haven't mentioned measuring them with Q5, Q6, and Q7 removed. You've measured lots of other things, and in general, I can't tell where you're measuring ON THE BOARD. I've asked what you meant by "in and out" - no answer. There is more than one circuit equivalent spot to measure many things on the board. Either way, you seem determined down the path of getting replacement boards vs. figuring out what exactly the problem is on the boards you have. It is important to verify and measure precisely on the boards if you are trying to trace out a board (or other) issue. That is why I've gone to the trouble of describing exactly where the measurement should be taken and the path of the traces. In the measurement I've asked you for at least twice, there is literally one (or there is supposed to be only one) trace of <1" between the parts. If you're not getting the proper measurement ...
... either you have not taken the measurement the way I've described, you have misbehaving measurement equipment, you have incorrect measurement technique, you have a faulty part, or you have found at least one clear issue (a short) with your boards and a starting point for determining what/where it may be.
tl;dr If you think it's a board manufacturing issue - I was trying to give you a path to definitively confirm or rule out that hypothesis.
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Once again... stop worrying about the schematic. Your circuit is not behaving like the schematic would indicate, and one of your hypotheses is that the boards are defective. So what good is the schematic except to frustrate you? You need to verify the traces on the boards. It's two resistors in series. You can use any values you want. If they're not measuring properly through the exact trace path I described (R11... tiny trace...R12) then there is an issue. Voila... you can start to unravel the sweater from there. Again, that holds true only if Q7 is removed (or functioning as intended) and there is no short between the pads for pin 1 and pin 2 of Q7.
If you have 4 boards that measure 221R where you should have 321R between the two spots on the board I've carefully described AND if both resistors measure 221R and 100R AND if Q7 is removed with no shorts between pads 1 and 2. Then it should take less than a few mins after to determine what one issue is. There may be more.
I'd lay odds that you haven't measured where I've asked with the parts removed on 4 boards. If you have, and the measurements are as reported, congratulations, you are thiiiiiiiiis close.
Clearly I am not describing my methodology well enough for you to simply execute and respond with the measurement requested vs. continuing to refer me to "above". For that, my apologies for wasting your time.
I really hope you get this worked out. You've spent what must be countless hours. We're rooting for you. I will leave you in the capable hands of the group.
It shows that voltage is flowing from your meter in two directions around the circuit. That is what my test showed also and the fundamental premise of electronics that you are missing is that voltage will take the path of least resistance. The 0.47 resistors at R13 and R14 are like shorts to your meter and they are connected to the mosfets which should not be like shorts. In my test Q6 and Q7 were shorts and it duplicated your results with the non-working boards. If Q6 and Q7 are not shorts then shorts must exist elsewhere in the circuit.
If you are unable to safely remove Q6 and Q7 from a working board can you isolate them by pulling a leg of the parts going into and out of it without damaging anything? now you would have the resistor/mosfet loop isolated and can measure it. Plus you can measure the working Q6 and Q7.
Claas writes:
"I agree. Could be wrong component somewhere, wrong direction of component, damaged component, or soldering issue."
Have stressed repeatedly that there are no problems with the parts, that they have been checked repeatedly, and that all continuity checks with the schematic have been made. You are wrong. The problem is with the boards.
"I agree. Could be wrong component somewhere, wrong direction of component, damaged component, or soldering issue."
Have stressed repeatedly that there are no problems with the parts, that they have been checked repeatedly, and that all continuity checks with the schematic have been made. You are wrong. The problem is with the boards.
IAIMH writes:
"Either way, you seem determined down the path of getting replacement boards vs. figuring out what exactly the problem is on the boards you have."
Inappropriate. You do not know my intentions and your conclusion is incorrect. Have gone to great lengths to check, recheck, and fix the boards I have. This comment does not move us forward. Have determined to my satisfaction that the boards have problems, have reported this to DIY and restate it here.
"Either way, you seem determined down the path of getting replacement boards vs. figuring out what exactly the problem is on the boards you have."
Inappropriate. You do not know my intentions and your conclusion is incorrect. Have gone to great lengths to check, recheck, and fix the boards I have. This comment does not move us forward. Have determined to my satisfaction that the boards have problems, have reported this to DIY and restate it here.
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IAIMH: The test you prescribe, from R11 to R12 has been done on a board with Q5, Q6, and Q7 removed and it is the same problem R -- 221. Again, as I mentionned repeatedly above, this cannot be based upon the schematic. And if it can be, then please tell me how.
Can you provide us with a schematic of the boards you have that shows where the problem is? This is very important because the MX2 is a popular amp and many boards are already in the hand of builders who like me have other projects to finish before starting the MX2. Only by showing this error can others be confident with the boards they have.
If it is not within your capacity to provide this schematic please refrain from stating that there is a problem with the boards.
If it is not within your capacity to provide this schematic please refrain from stating that there is a problem with the boards.
SL states:
"Can you provide us with a schematic of the boards you have that shows where the problem is?"
What does this mean? Am using the same schematic we are all -- on page 1 above. If I knew where the problem was, I would have told everyone. Have stressed to all that one board provides the correct path from R14 to Pin 2, 4N35 and three do not. They were all built accurately and have no soldering issues. Noone has been able to explain why this is ocurring. Thus, I am left with a board problem as has been discussed.
"Can you provide us with a schematic of the boards you have that shows where the problem is?"
What does this mean? Am using the same schematic we are all -- on page 1 above. If I knew where the problem was, I would have told everyone. Have stressed to all that one board provides the correct path from R14 to Pin 2, 4N35 and three do not. They were all built accurately and have no soldering issues. Noone has been able to explain why this is ocurring. Thus, I am left with a board problem as has been discussed.
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If you can not draw a schematic of the connections (traces) on your boards and how they differ from the published schematic then you can not say that there is a problem with the boards you have. The schematic would be created by starting a point on the board and using a continuity test verify that a solder pad has connection with the solder pads shown in the original schematic. Then continue around the board verifying all traces on the board. This is a very simple process. If you do not posses the technical skill to complete this schematic then you are not able to state that there is a problem with the board.
It's quite possible to create your own re-layout of the M2x_ChA and M2x_ChB PCBs. The excellent layout program KiCad is open source and completely free (link) and that's just one choice among many.
Create the footprints, place the components, route the nets, run thru DRC/ERC, export to Gerber, and upload the files to a PCB fab's website. It'll be a lot of fun, both learning and doing. Afterwards, you can consider laying out one or more M2x input stage daughter cards, either copying one of the existing circuit designs, or adding some modifications* & improvements of your own. Even more fun.
*for example: borrow the IPS7 idea of accepting either a dual-opamp chip or a single-opamp chip, and implement it on Tucson. Victory!
Create the footprints, place the components, route the nets, run thru DRC/ERC, export to Gerber, and upload the files to a PCB fab's website. It'll be a lot of fun, both learning and doing. Afterwards, you can consider laying out one or more M2x input stage daughter cards, either copying one of the existing circuit designs, or adding some modifications* & improvements of your own. Even more fun.
*for example: borrow the IPS7 idea of accepting either a dual-opamp chip or a single-opamp chip, and implement it on Tucson. Victory!