Nothing.? The Linear continues to produce 3.3V relative to it's 'GND' pin. if the supply produced by the SMPS is more then it provides nothing.? All this is confused by D102 andD103 which prevent the linear getting a voltage on its output which it can't cope with.

Chris, G5CTH

On 29/08/2023 19:40, Jonathan Burchmore wrote:

What is the mechanism that reduces the voltage on LIN_REG_IN during that half-way state from the supply voltage to 3.3V? ?It seems to me that the supply voltage passes through Q103 & Q105 (on the 5V board), then R101 on the 3v3 board and is directly connected from there to PD7 on the processor.

Jonathan KN6LFB

What is the mechanism that reduces the voltage on LIN_REG_IN during that half-way state from the supply voltage to 3.3V? ?It seems to me that the supply voltage passes through Q103 & Q105 (on the 5V board), then R101 on the 3v3 board and is directly connected from there to PD7 on the processor.

Jonathan KN6LFB

I have on of those QRPGuys SWR indicators. I've just not built it, yet. I wonder if I should us that or find and absorptive bridge. I'm planning to use a resonant linked dipole with the QDX when out in the field.

Hello Stephan

?

I think that given all of the people experiencing blown components due to power supply issues (including myself), there is a case to be made for a redesign of the power supply. Something like an can replace 38 parts in the current design with 8, with significantly better performance in every way. The frequency of the part can be externally synchronized, but you can also simply configure it for 2.2 MHz, where every harmonic is a minimum of 400 kHz from any of the amateur bands covered by the QMX.

Yes but...?

1. What about the eye-watering price? There are two versions in stock at Digikey, LTM8078IY and LTM8078EY. The price at 520-quantity?(1 tray) is $11.52 and $10.47 resp. Plus taxes of course... for comparison, since I have the two SMPS boards on the QRP Labs shop at $10? I'm sure you can imagine that the parts costs are way way less than one of these LTM8078; consider that the $10 price also includes the 6-layer PCB, the two female header connectors, SMD assembly factory costs, shipping, taxes, other costs etc.?

2. One of the main reasons for using a discrete component buck converter when the QDX Rev 3 PCB was designed, having the discrete component buck converter for the PIN diode forward bias generation, was that the global semiconductor crisis was in full swing, and adding an unusual part to the BOM seemed distinctly unattractive compared to a handful of discrete parts which are much easier to find. The QMX design inherited the buck converter from QDX. Whilst the global semiconductor crisis has receded somewhat we are still nowhere near back to the old days where you never ever thought about availability because you never had to. Looking at the available stock in Digikey (1050 of the EY and 3410 of the IY) isn't terribly encouraging in that regard.?

3. Being a BGA package, replacement would truly be beyond the reach of most of us here...

4. We are getting through building a larger and larger number of QMX now that the whole team are building them here. Originally, while we still had a long list of QDX, QCX-mini and QCX+ on the waiting list, only one (the most experienced and accurate) team member was building them, in order to build up experience of potential hazards. Of all the QMX I have yet seen, other than the Q103/Q104 Drain short (manufacturing problem) I have yet to see a failure that is not attributable to shorts, damaged components or other construction errors.?

73 Hans G0UPL

Thanks Paul. I realize that they may be blown, but from my recollection they didn't continue shorted. Low power out was the usual symptom IIRC. This is a complete short immediately on power on.

73,

Cliff, AE5ZA

On Aug 28, 2023, at 18:25, Paul - AI7JR <paul.hanchett@...> wrote:

Most likely culprits are going to be the BS170's, and possibly IC503, from other reports.

Paul -- AI7JR

On 8/28/23 15:32, Cliff wrote:

Well, guys, I'm up a creek it seems here. I'm an old guy, raised on Tubes, and don't really understand Mosfets and the schematics for the QMX are hard for me to follow.

Some suggestions to trace the issue here would be much appreciated.

I built this QMX about 3 1/2 months ago. It's been working FB with firmware 006 ever since. This morning I was using it and transmitted accidentally with no antenna attached. It's happened before with no consequences, but this time something shorted out big time. The power supply went into current limiting at 1 amp with the voltage dropped to 6 volts. Powered off with a BIG SIGH!

Opened it up and just a little smell of hot electronics, but not the usual burnt smell. Inspecting all the boards and nothing obviously burned.

Lowered the voltage to 7 volts and current limiting to 600 mA. Pushed the encoder to power up and nothing happens. Raised the power back to 12V and with one hand on the power off switch pushed the encoder. Current started climbing rapidly so power off quickly.

Tried to figure out the schematics and I get lost with all the plug numbers not being consistent between pages and some times I see multiple connector diagrams like JP101 and JP102 that seem identical as well as new to me symbols, etc. and Not really knowing how things work in the sequence I finally started this email.

Obviously something in the power up sequence has shorted, but how to trace it I'm totally at a loss.

Some help/ideas will be greatly appreciated.

Thanks!!!

73,
Cliff, AE5ZA

Was successful today with WS (See picture) but not without hassle I believe caused by Windows OS and not the radio. About the time I think I have the turn on/connect/ enter sequence down pat something seems different!

Trying to establish CAT over the usb cable is prone to interference from what you have had CAT before. It's like there are "leftovers" that interfere with the present task. When shifting to fldigi from WSJT-X the same radio is generally a breeze like with my mcHF clone. But going there with the QMX after the mcHF.. forget about it! The CAT is incomplete with the QMX since here, anyway, frequency is not automatic. Neither is band switching with the computer.
--
73
Karl
KI4ZUQ

On Aug 29, 2023, at 11:43, Cliff <ae5zaham@...> wrote:

Well, Steven I owe you on this one. You called it right to the component. The short was on the 5V rail and the component was D108. That is sure a tiny little diode. Going to be fun to put a new one in.

Now the fun of trying to find a part number for that diode. The parts list only gives the specs, not a part number.

73,

Cliff, AE5ZA

On Aug 29, 2023, at 01:24, Stephan Ahonen KE0WVA <stephan.ahonen@...> wrote:

A thermal camera is hands down the best way to identify a shorted component. Turn on the power and look for the thing that glows. You can get one that attaches to your phone for about $2-300.

A multimeter in continuity mode is the second best way.

First order of business is to test for continuity from ground to each of the three voltage rails. The 2x4 and 2x3 headers that the power supply boards attach to are good places to do this.

To map the drawing of JP101-4 to the physical layout on the board, look at the board from the bottom side, i.e. the side with the microprocessor on it, with all of the through-hole components facing away from you. Turn the board until the antenna connector is pointing up, and the DC input jack is pointing down. The solder pads for the headers are now in the same orientation as they are in the schematic. But don't trust me on this, use your multimeter to verify ground (the body of the antenna connector is a convenient place to test this from) and Vin (use the center of the DC input jack) at minimum. This should be enough to make you confident.

If you are seeing a short from ground to either VCC (the +5 volt rail) or VDD (the +3.3 volt rail), try removing the associated power supply board and see if the short is still there. If the short went away when you removed the power supply board, the likely culprit is a failure of D108/9, or one of the tantalum capacitors C106/7. If the short persists with the power supplies removed, you have had a failure of one of the many ICs on your main board, and it's time to decide how you value your time, money, and energy. Be aware that even if you find and replace the failed component, the same event could have damaged other components without totally destroying them, and you could boot up your radio to find that still more work needs to be done. I had this realization after I managed to make my QMX boot again by removing IC403, and weighed the cost of buying and shipping a replacement IC in single digit quantity, and ended up just buying another QMX. Maybe I'll use the old one as a source of spare parts for the new one if I manage to fry that one too.

If the short you're finding is +12V to ground, again try to see whether the short is in the power supply board or in the main board. Luckily, not too many components are actually hooked up to +12V, at least in a way that makes them liable to short to ground.

Based on your symptoms: The board stays powered after releasing the encoder, which means the CPU is awake and putting voltage on the PWR_HOLD line, which means that the 3.3V rail is good. But no display, and the display runs on the 5V rail. So I would say the issue is somewhere on the 5V rail.

On Aug 29, 2023, at 01:24, Stephan Ahonen KE0WVA <stephan.ahonen@...> wrote:

A thermal camera is hands down the best way to identify a shorted component. Turn on the power and look for the thing that glows. You can get one that attaches to your phone for about $2-300.

A multimeter in continuity mode is the second best way.

First order of business is to test for continuity from ground to each of the three voltage rails. The 2x4 and 2x3 headers that the power supply boards attach to are good places to do this.

To map the drawing of JP101-4 to the physical layout on the board, look at the board from the bottom side, i.e. the side with the microprocessor on it, with all of the through-hole components facing away from you. Turn the board until the antenna connector is pointing up, and the DC input jack is pointing down. The solder pads for the headers are now in the same orientation as they are in the schematic. But don't trust me on this, use your multimeter to verify ground (the body of the antenna connector is a convenient place to test this from) and Vin (use the center of the DC input jack) at minimum. This should be enough to make you confident.

If you are seeing a short from ground to either VCC (the +5 volt rail) or VDD (the +3.3 volt rail), try removing the associated power supply board and see if the short is still there. If the short went away when you removed the power supply board, the likely culprit is a failure of D108/9, or one of the tantalum capacitors C106/7. If the short persists with the power supplies removed, you have had a failure of one of the many ICs on your main board, and it's time to decide how you value your time, money, and energy. Be aware that even if you find and replace the failed component, the same event could have damaged other components without totally destroying them, and you could boot up your radio to find that still more work needs to be done. I had this realization after I managed to make my QMX boot again by removing IC403, and weighed the cost of buying and shipping a replacement IC in single digit quantity, and ended up just buying another QMX. Maybe I'll use the old one as a source of spare parts for the new one if I manage to fry that one too.

If the short you're finding is +12V to ground, again try to see whether the short is in the power supply board or in the main board. Luckily, not too many components are actually hooked up to +12V, at least in a way that makes them liable to short to ground.

Based on your symptoms: The board stays powered after releasing the encoder, which means the CPU is awake and putting voltage on the PWR_HOLD line, which means that the 3.3V rail is good. But no display, and the display runs on the 5V rail. So I would say the issue is somewhere on the 5V rail.