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mission impossible? QRP labs QMX power supply boards

 

In an earlier post I described how, after endless trouble shooting I fried my on-board supplies...Thinking back i am wondering if I plugged in the 13.8v as opposed to the 12v line I reduced with diodes...in any event, I fried the CBT chip and, as I later discovered, the zener diode on one of the little daughter boards. Thinking I may have found an easy fix, I replaced the zener with a thru hole type...no joy, I am just seeing the nominal 12v.? off of the boards
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So, I am wondering about the feasibility of fixing the boards? I have already ordered a couple more kits but who knows when they will get shipped as Hans is waiting on some parts himself...I can get mouser delivered in about a week up here in Canada's Yukon. Aside from the obvious shotgun approach, any suggestions as to where to attack this? That little zener was the only one to show any physical damage on the daughter board.?
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I realize fully that even fixing these boards may not cure the rig and that in fact other components may have gone out as well--even without the magic smoke.
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Appreciate any thoughts the collective might have.?
 

I have successfully replaced diodes on those little boards, and in the wiki here there is a description of how to do stand-alone testing on them.?
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But it is easier to buy the inexpensive replacement tested power supply boards from qrp-labs, and you won't have to wait in the queue for the full kits.
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Stan
 

I have a spare pair of boards but I am in AU.
Cheers
David
 

I made a board with a couple of linear regulators to replace the boards.? It uses more power but is much more robust.
Those are TO-220 packages with most of the tab clipped off.
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Chris, G5CTH
 

Very interesting.
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Any chance for more details?
Circuit diagram?
Parts list?
Basic Performance specs?
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I would love to cobble up one or two just to learn and eval myself.
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GREG
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Here's the schematic, not terribly complex:
It's built on strip board, most of the resistors are SMD types on the other side. The regulators are generic types and the capacitors are what their data sheet suggested.
Two things: R1 is required ensure that PWR_ON is pulled up when it's being used as a normal button and R6 pulls the ADC_5V line a little high as otherwise the PWM the MCU generates is too high.? Something similar may be needed across R4.
It's got no power on/off.? The regulators get a bit warm but nothing excessive, I tend to keep the voltage down unless I've got a good reason to increase it, no more than 12V of course.
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Chris, G5CTH
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Outstanding. Thank you very much. Should/could be handy for a lot of reasons and future projects.?

I'm going to rummage through my spares and hit Mouser later today for data sheets and pieces parts.?

GREG KI4NVX?




On Sun, Dec 22, 2024 at 8:28 AM, Chris
<chris.rowland@...> wrote:
Here's the schematic, not terribly complex:
It's built on strip board, most of the resistors are SMD types on the other side. The regulators are generic types and the capacitors are what their data sheet suggested.
Two things: R1 is required ensure that PWR_ON is pulled up when it's being used as a normal button and R6 pulls the ADC_5V line a little high as otherwise the PWM the MCU generates is too high.? Something similar may be needed across R4.
It's got no power on/off.? The regulators get a bit warm but nothing excessive, I tend to keep the voltage down unless I've got a good reason to increase it, no more than 12V of course.
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Chris, G5CTH
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Note:
  • You need a 220K parallel to the top 22K resistor for Vdd supply also. Otherwise if it works, it's just working by chance (component tolerances). You need that to convince the firmware that it's SMPSs are OK and continue with the rest of the power up sequence.
  • You lost reverse polarity protection?
  • You lost the soft power on/off. You can still use long left button press to save the QMX operating state (frequency, volume etc) and shut down, it just won't really switch off the power.?
  • I can't see a future problem now but I suppose it can't be guaranteed that future firmware versions would be compatible with it.?
  • Doesn't apply to QMX+ after Rev 1 because QMX+ has the SMPS integrated on board.?
73 Hans G0UPL


On Sun, Dec 22, 2024, 16:28 Chris via <chris.rowland=[email protected]> wrote:
Here's the schematic, not terribly complex:
It's built on strip board, most of the resistors are SMD types on the other side. The regulators are generic types and the capacitors are what their data sheet suggested.
Two things: R1 is required ensure that PWR_ON is pulled up when it's being used as a normal button and R6 pulls the ADC_5V line a little high as otherwise the PWM the MCU generates is too high.? Something similar may be needed across R4.
It's got no power on/off.? The regulators get a bit warm but nothing excessive, I tend to keep the voltage down unless I've got a good reason to increase it, no more than 12V of course.
?
Chris, G5CTH
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I produced my linear PSU board because I wanted a reliable and robust supply to provide the required voltages and survive mistakes such as a probe slipping.? I am prepared to live with higher current demand.
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On Sun, Dec 22, 2024 at 07:33 AM, Hans Summers wrote:
Note:
  • You need a 220K parallel to the top 22K resistor for Vdd supply also. Otherwise if it works, it's just working by chance (component tolerances). You need that to convince the firmware that it's SMPSs are OK and continue with the rest of the power up sequence.
Yes, I know, and said this in my notes.? Mine is just about OK.
?
  • You lost reverse polarity protection?
Yes, I considered adding a diode in series or crowbar diode protection but decided I would be careful.? I routinely use polarised plugs for supplies so only need to get it right once.? People are fee to add a diode, a 1N4001 would do the trick.

  • You lost the soft power on/off. You can still use long left button press to save the QMX operating state (frequency, volume etc) and shut down, it just won't really switch off the power.?
Yes, I know about the long button press and I can plug and unplug the power supply.
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  • I can't see a future problem now but I suppose it can't be guaranteed that future firmware versions would be compatible with it.
That's up to you, I don't think that you will change the firmware just to break this.
?
  • Doesn't apply to QMX+ after Rev 1 because QMX+ has the SMPS integrated on board.?
I think you made a mistake doing that.? You have a power regulator circuit that's been a constant source of trouble, that attempts to protect voltage critical components using a crowbar Zener diode which regularly fails, destroying itself, and sometimes other components in the power supply. You rely on the zener failing short circuit and the voltage drop shutting the MCU down.? I think that relying on a failure mode to protect voltage critical components is folly.? Are the PCM1804 failures down to momentay voltage spikes?
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When this was all on a cheap, easily replaceable board this was sort of OK, users could buy replacement boards and no more construction expertise was need that to build the kit in the first place.? Now when the power controllers fail the user has the option of replacing the entire main board or replacing SMD components - if the board survived.
?
The original use of this circuit was fine, to produce the TX bias, because it doesn't connect to any voltage critical components.? That's actually a current regulator isn't it?
?
And the justification for this - that the PWM frequency could be adjusted to avoid birdies - has never been implemented.? The PWM frequency is fixed and people are reporting birdies.
?
I must admit that I'm considering getting a QMX+ in spite of the board mounted power controllers.? If they fail I can work round it - put linears on the prototype board - but would really have preferred that the power controllers were still on a separate board.
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Chris, G5CTH
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This thread has turned into a rather active discussion...I appreciate everyone's input--including the man himself.
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All of that notwithstanding, given I am at the mercy of deliveries from the other side of the planet, is it feasible to simply connect 2 separate supplies of 3 and 5 volts? Its really more for the purpose of continuing the trouble shooting than a long term solution--I am simply not sure if there is some sort of interplay between the little boards that would not make this possible. If it is, seemingly i could apply the separate 3 and 5 volt inputs and carry on 'fixing' my radio???
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I now have 3 orders in the cue at QRP LABS with the addition of the pwr supply boards.?
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Again, i appreciate everyone's input and assistance.
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scott vy1co?
 

Scott wrote:? "is it feasible to simply connect 2 separate supplies of 3 and 5 volts?"
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You can, though not quite so simply.? The processor waits till the power supplies are up before continuing on with getting the radio to work.? It senses if the power supplies are up through the signals ADC_3V3 and ADC_5V, so you also have to implement R110,111,112,113.
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In addition, Hans suggests you add 100k resistors in parallel with the 22k resistors at R112 and R113:
/g/QRPLabs/message/133787
That drops the value of those 22k resistors to around 18k, I'd think anything between 18k and 20k would do.? This is needed because if the processor senses the voltage to be a little bit low it continues to wait, but if the voltage is a little bit high it continues on with the next step.?
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Know that the protection Zeners are on the missing power supply boards, so triple check that your 3.3 and 5v regulators are set for the correct voltage before connecting them to the radio.? Power down the supplies, connect them to the radio, then power up.
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Jerry, KE7ER
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Hi Chris
  • I can't see a future problem now but I suppose it can't be guaranteed that future firmware versions would be compatible with it.
That's up to you, I don't think that you will change the firmware just to break this.

Certainly not intentionally. I can't foresee any scenario where it could be broken. Or where, if I had some reason for some kind of extra failsafe, I could have a parameter to switch it off.?

I think you made a mistake doing that.? You have a power regulator circuit that's been a constant source of trouble,

That depends on what the source of trouble is. If the circuit itself is at fault, design faults causing the constant source of trouble, then indeed making it part of the QMX+ board would have been a mistake.?

On the other hand if the power regulator circuit has been a constant source of trouble because soldering on the connectors accurately and physically aligning, without errors, shorts, bad connections etc.: then incorporating the supplies on the main board was exactly what was required to solve it.?

If the power regulator circuit has been a constant source of trouble because of component defects in manufacturing then again, incorporating them on the main board, which allows us to do full testing before shipping anything, was also exactly the right thing to do.?

I'm not sure what evidence there is to suggest there are design faults that cause trouble, rather than construction faults? How many problems do we hear reported for QMX+ Rev 2 boards SMPS circuits compared to those of QMX+ Rev 1 boards and QMX?

that attempts to protect voltage critical components using a crowbar Zener diode which regularly fails, destroying itself, and sometimes other components in the power supply. You rely on the zener failing short circuit and the voltage drop shutting the MCU down.? I think that relying on a failure mode to protect voltage critical components is folly.?

There are multiple fail-safes and the zener is only intended as a last resort.?

Are the PCM1804 failures down to momentay voltage spikes?

There's nothing to indicate or suggest this.

The original use of this circuit was fine, to produce the TX bias, because it doesn't connect to any voltage critical components.? That's actually a current regulator isn't it?

Sort of... It still regulates voltage but it chooses the voltage according to a model of what voltage is required to drive the target current.?

?And the justification for this - that the PWM frequency could be adjusted to avoid birdies - has never been implemented.? The PWM frequency is fixed and people are reporting birdies.

Yes, that needs to be done too... My list is indeed long these days.??

73 Hans G0UPL
 

Looks like my last post has material that's already covered in this thread.
Hans is now recommending 220k instead of 100k in parallel with the 22k at R112 and R113, for a resultant value of 20k.
And Hans is correct, you lose the rather nice power-on/power-off scheme.
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I agree with Chris that the power supplies should be revisited, though understand that the board won't be changed anytime soon as Hans has bigger fish to fry.? That's fine with me, it works well enough for most of us.? I'm convinced that the long term goal should be for the QMX to use commercially available IC's in the SMPS's.
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I was able to implement linear regulators by plugging a new daughterboard into JP105 of the QMX+.
In addition, I had to make a few mods to the main board, the mods I did could be reduced to:
Remove Q106 and Q107 (to disable the 3.3v and 5v PWM drive) and short across Q111 (so ADC_3V3
sees the new 3.3v regulator).? And of course, add 220k resistors across R112 and R113.
I also disabled the 78M33 regulator, though that is probably not necessary.
We could avoid all of those mods and just short from Q101's gate (LIN_REG_EN) to Q101's source (Ground) if the firmware were slightly adjusted:
In that post I state: "Shorting Q101's gate to source is still necessary, of course."
By which I meant to short those pins if the firmware is updated to accomodate my hack, that being the only hardware mod required.
But with currently available firmware you should not short Q101's gate to source, as that grounds the STM32F IO pin driving LIN_REG_EN.
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This post also pertains to this issue:
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Jerry, KE7ER
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On Sun, Dec 22, 2024 at 11:42 AM, Chris wrote:

I produced my linear PSU board because I wanted a reliable and robust supply to provide the required voltages and survive mistakes such as a probe slipping.? I am prepared to live with higher current demand.
?
On Sun, Dec 22, 2024 at 07:33 AM, Hans Summers wrote:
Note:
  • You need a 220K parallel to the top 22K resistor for Vdd supply also. Otherwise if it works, it's just working by chance (component tolerances). You need that to convince the firmware that it's SMPSs are OK and continue with the rest of the power up sequence.
Yes, I know, and said this in my notes.? Mine is just about OK.
?
  • You lost reverse polarity protection?
Yes, I considered adding a diode in series or crowbar diode protection but decided I would be careful.? I routinely use polarised plugs for supplies so only need to get it right once.? People are fee to add a diode, a 1N4001 would do the trick.

  • You lost the soft power on/off. You can still use long left button press to save the QMX operating state (frequency, volume etc) and shut down, it just won't really switch off the power.?
Yes, I know about the long button press and I can plug and unplug the power supply.
?
  • I can't see a future problem now but I suppose it can't be guaranteed that future firmware versions would be compatible with it.
That's up to you, I don't think that you will change the firmware just to break this.
?
  • Doesn't apply to QMX+ after Rev 1 because QMX+ has the SMPS integrated on board.?
I think you made a mistake doing that.? You have a power regulator circuit that's been a constant source of trouble, that attempts to protect voltage critical components using a crowbar Zener diode which regularly fails, destroying itself, and sometimes other components in the power supply. You rely on the zener failing short circuit and the voltage drop shutting the MCU down.? I think that relying on a failure mode to protect voltage critical components is folly.? Are the PCM1804 failures down to momentay voltage spikes?
?
When this was all on a cheap, easily replaceable board this was sort of OK, users could buy replacement boards and no more construction expertise was need that to build the kit in the first place.? Now when the power controllers fail the user has the option of replacing the entire main board or replacing SMD components - if the board survived.
?
The original use of this circuit was fine, to produce the TX bias, because it doesn't connect to any voltage critical components.? That's actually a current regulator isn't it?
?
And the justification for this - that the PWM frequency could be adjusted to avoid birdies - has never been implemented.? The PWM frequency is fixed and people are reporting birdies.
?
I must admit that I'm considering getting a QMX+ in spite of the board mounted power controllers.? If they fail I can work round it - put linears on the prototype board - but would really have preferred that the power controllers were still on a separate board.
?
Chris, G5CTH
 

Hi Jerry

Hans is now recommending 220k instead of 100k in parallel with the 22k at R112 and R113, for a resultant value of 20k.
And Hans is correct, you lose the rather nice power-on/power-off scheme.

I don't recommend the mod at all; but I'm saying if you insist on doing it, then you need some kind of ADC voltage somewhat higher than half the rail voltage so that the processor thinks it's SMPS control loops are all working OK and it can proceed past waiting for the supplies to come up. 100K, 220K, it isn't terribly critical.?

73 Hans G0UPL
 

Hans,
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Understood.? I would not recommend modding the QMX for most builders either.? Significant hacks are way more likely to trash a QMX than the few incidents of SMPS failures.
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Chris wrote:? "Are the PCM1804 failures down to momentay voltage spikes?"
Hans replied:? "There's nothing to indicate or suggest this."
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There are lots of PCM1804 failures though, would be nice to get to the bottom of that. My impression from following this forum is that PCM1804 failures are mostly on the QMX, not on the QDX which has linear regulators.? I could be wrong in that.? If true that at least indicates something, though is by no means definitive.
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Many have trouble with momentary shorts of the power supplies given the minimal clearances. Would be interesting to evaluate how one of those standalone 5v SMPS boards recovers from a momentary VCC short, will need a processor working the ADC_5V and PWM_5V signals.? I'd expect to see a spike.
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If we do decide to change the QMX+ power supplies, an easy retrofit is to solder a daughterboard down to header pins on JP105, plus the firmware mod to inspect for a short from LIN_REG_EN to ground at initial power up.? Daughterboard could have linear regulators or switcher IC's.? If the daughterboard is tested before shipping and the mod is kept as simple as a board install and a solder glob across two Sot23 pins (I'm good at that), should be an easy enough upgrade for most kit builders.
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Jerry, KE7ER
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On Sun, Dec 22, 2024 at 01:15 PM, Hans Summers wrote:

Hi Jerry
?
?
Hans is now recommending 220k instead of 100k in parallel with the 22k at R112 and R113, for a resultant value of 20k.
And Hans is correct, you lose the rather nice power-on/power-off scheme.
?
I don't recommend the mod at all; but I'm saying if you insist on doing it, then you need some kind of ADC voltage somewhat higher than half the rail voltage so that the processor thinks it's SMPS control loops are all working OK and it can proceed past waiting for the supplies to come up. 100K, 220K, it isn't terribly critical.?
?
73 Hans G0UPL
 

Hello Jerry
?
Chris wrote:? "Are the PCM1804 failures down to momentay voltage spikes?"
Hans replied:? "There's nothing to indicate or suggest this."
?
There are lots of PCM1804 failures though, would be nice to get to the bottom of that. My impression from following this forum is that PCM1804 failures are mostly on the QMX, not on the QDX which has linear regulators.? I could be wrong in that.? If true that at least indicates something, though is by no means definitive.

It's wrong. I also thought like you, however I was not informed by my team until recently, that QDX had been failing their pre-shipment testing. It seems that our testing of QDX and QMX+ Rev 2 picks up issues with PCM1804 but testing with QMX does not (needs improvement). So it appears that the PCM1804 problem is not caused by the SMPS on QMX, because it affects QDX also (which has linear supplies). This indicates PCM1804 is a separate unrelated issue.?

73 Hans G0UPL
 

Hans,
?
Thanks for the response.
These PCM1804 failures are puzzling.
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Jerry, KE7ER

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