Nono - R4/R6 on the SLB get hot. Because I can see R18 smoking ... I turn off quickly - so I don't know whether any resistors on the AN 4R board are getting hot.
Andy
It's a matter of current draw from the SLBs, JT.
As I have 21v DC rails, a 6.7 ohm resistor array on each rail draws 3.2a - which is equivalent to the bias current drawn by an AN 4R board. (Your 8R boards are only biased at 1.7a, right?)
Andy
Under normal Class A operation up to 5A, R4/R6 are supposed to get hot, up to 150C (which is within spec) but can burn your fingers if you touch it. 5A over 0.1ohm is 2.5W.
But R18 should not be smoking. How warm does the pass-BJT get when all of this is happening? Cold or warm? If cold, it means all the current is passive g through the smaller resistors. If warm or hot, possibly there is oscillation.
Another test is to simply add a 2ohm power resistor in series between the SLB and amp to increase the apparent impedance load presented by the amp. So the other thing that could be a problem is that the amp is not working and is acting as a dead short. Have you verified the amp is working and not drawing excessive current beyond rated capacity?
Please measure current across R4 or R6 on SLB to see what the current load is when this is happening. Is it more than 3.2A? Specifically is it more than 5A?
Yes, that's what I thought, X. So I was surprised that they only got a bit warm when I had the 6.7 ohm dummy-load resistors on the SLB's DC rails.
But then - at only 3.2a current draw - that's only 1w through each 0.1 ohm resistor!
Given R18 was smoking, I haven't waited long enough to touch the BJTs, X.
I'm not quite sure how I can do this verification?
Mmmm, sorry - given R4 and R6 sit right against the pcb - as do the caps either side of these resistors - I can't quite see where I can put my meter probes to take these measurements?
Andy
Yes, about 1.72A if I remember correctly. So if you are drawing 3.2 per rail, you should be good with the SLB... R4-5 get hot, but are only warm when connected the your dummy load, so we know that the AN is drawing way more than 3.2A per rail.
So, you know it's the AN board which is the issue for one reason or another. I follow, but that's about all. I don't know enough to help.
A little advice please.
I just wired up my new PSU with 20v toroidy transformer and SLB.
Turned on fine, measured +/- 29v. Hooked up to amp board and got ~28.
I hooked up speakers, and played music, which sounded fine, just started. When I looked back at the amp, it was smoking, and I had burnt R13.
Also, the LEDs did not light, I suppose I could have put them in backwards...
Suggestions?
I just wired up my new PSU with 20v toroidy transformer and SLB.
Turned on fine, measured +/- 29v. Hooked up to amp board and got ~28.
I hooked up speakers, and played music, which sounded fine, just started. When I looked back at the amp, it was smoking, and I had burnt R13.
Also, the LEDs did not light, I suppose I could have put them in backwards...
Suggestions?
Check Q10 if you have it wrong the resistor takes the load and poof. Also, look at all the solders in the area, the board is very hard to flow in places.
Kind of strange though, how long did it run before the R13 smoked? Disconnect the MX2 replace R13 and check BCE values. If okay, drop a load on the power supply only and see if R13 starts to get hot fast. When I had an issue there, I just pulsed the power under load and it got hot very fast. Mine turned out to be a solder issue I re flowed everything from R9 and all was well.
I also had one have an issue with the flying leads and a mis-wire, it will do the same thing, smoke R13.
Kind of strange though, how long did it run before the R13 smoked? Disconnect the MX2 replace R13 and check BCE values. If okay, drop a load on the power supply only and see if R13 starts to get hot fast. When I had an issue there, I just pulsed the power under load and it got hot very fast. Mine turned out to be a solder issue I re flowed everything from R9 and all was well.
I also had one have an issue with the flying leads and a mis-wire, it will do the same thing, smoke R13.
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TT has good suggestions. It may be that you have a bad solder joint and cap Mx was not working (nothing passing through large BJTs). Your voltage appears to have no dropout (should be about 3v drop) so looks like BJTs not working so all current flows through tiny R13.
Forget the V Bones, that isn't the issue... You have skillz, let us know what it was when you figure it out.
One suggestion... Eliminate one variable at a time; Look at the supply only, load it... R13 smoke? No, then it's the MX2 board, which I doubt. My guess is flying lead issue, or solder flow issue.
Post it when you know, to help those that come after.
One suggestion... Eliminate one variable at a time; Look at the supply only, load it... R13 smoke? No, then it's the MX2 board, which I doubt. My guess is flying lead issue, or solder flow issue.
Post it when you know, to help those that come after.
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It’s not the M2x board, that has worked great for months.
My plan, for tomorrow, is to use the other SLB board (monoblocks) and solder the flying leads to the board directly. If I can get that to work right, I’ll work on getting the R13 out, and check to see if I have another one in my resistor stash.
My plan, for tomorrow, is to use the other SLB board (monoblocks) and solder the flying leads to the board directly. If I can get that to work right, I’ll work on getting the R13 out, and check to see if I have another one in my resistor stash.
Switched out one SLB board for the other, cut off the Molex, and soldered the fly leads directly to the transistor holes.
Smooth start up, no smoke. Unloaded output was right at 29v, both +/-.
Hooked up the amp board, and got 26v both +/-. Music sounds good.
In my mind, I clearly have not implemented the molex based fly leads, causing the failure.
Now on to trying to repair the first SLB board.
Thanks for the help guys!
Smooth start up, no smoke. Unloaded output was right at 29v, both +/-.
Hooked up the amp board, and got 26v both +/-. Music sounds good.
In my mind, I clearly have not implemented the molex based fly leads, causing the failure.
Now on to trying to repair the first SLB board.
Thanks for the help guys!
Well done!
Very easy to do - the Molex connectors have caused problems with my build.
My view is that a much more robust solution would've used enough real-estate to have spades - marked with a '1', '2' & '3'.Andy
Ordered 10x R13. When they get here, I will get out the de-solder iron, and try to get it out, and open up the holes enough to put the new one in. Next weekend before I have time most like. I will keep in mind mounting it to the undercarriage as a possibility.
Wife's birthday next Saturday, I can't spend the day messing around with my de-solder iron.
Fortunately, both the M2x amps are singing now, just one has a new PSU.
Wife's birthday next Saturday, I can't spend the day messing around with my de-solder iron.
Fortunately, both the M2x amps are singing now, just one has a new PSU.
Good news your up and running Bones13!
To remove R13, wedge a very small flat screwdriver between the resistor body and pcb board. (Be careful not to scratch off the solder mask) Get a molten ball of solder on your tip and heat the one leg of the resistor from the bottom side, when the solder melts gently pry upward with the screwdriver until the leg is free from the hole. Now grab the free end with needle nose pliers and heat the other side from the top, it should pull right out.
To remove and clean out the old solder from the holes you need one of these handy suckers: https://www.amazon.com/Solder-Sucke...cphy=9004589&hvtargid=pla-1009492819148&psc=1
Now your good to go with your new resistor
To remove R13, wedge a very small flat screwdriver between the resistor body and pcb board. (Be careful not to scratch off the solder mask) Get a molten ball of solder on your tip and heat the one leg of the resistor from the bottom side, when the solder melts gently pry upward with the screwdriver until the leg is free from the hole. Now grab the free end with needle nose pliers and heat the other side from the top, it should pull right out.
To remove and clean out the old solder from the holes you need one of these handy suckers: https://www.amazon.com/Solder-Sucke...cphy=9004589&hvtargid=pla-1009492819148&psc=1
Now your good to go with your new resistor
I have a de-solder gun, with a pump in it. But with this tiny leads, removing the resistor might be better controlled with the regular solder iron. Then pick up the solder with the gun.
I use hemostats to grip items, easier to control when I’m using the hot iron in the other hand. Worth pulling out the PCB holder too.
I’m open to any advice �� though, I’m a good surgeon, but fair to poor electronic technician when the project does not turn on.
I use hemostats to grip items, easier to control when I’m using the hot iron in the other hand. Worth pulling out the PCB holder too.
I’m open to any advice �� though, I’m a good surgeon, but fair to poor electronic technician when the project does not turn on.
When desoldering, DO NOT pull the component until AFTER the solder melts. Otherwise you risk removing (medical term: evulse-ing) the copper pad on the component side of the board. When you pull before all solder is fully melted, you yank away: cold solder and cold copper on the non-heated side of the board. This is not what you are hoping for, young padewan.
Ask me how I know this.
Ask me how I know this.
Yes, I have lifted traces, and pads, before. (And repaired some of my errors) Patience seems to be a virtue in the component replacement arena. I have gotten better with the suction pump de-solder gun. I was really terrible with the iron, and the solder wick. It does appear that I only need to replace the R13, so it should not be too onerous.
