Wow! Thank you all for the responses. I'm thinking I'm going to give the TN0606 a try, and use some thermal grease. Thanks for that hint.
I'm about to expose my real lack of knowledge by asking what might be a dumb question. An SWR bridge provides a 50 ohm impedance to the radio while SWR is read? I that hos that works?
Thanks,
Wayne
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Re: QMX - smoke - another C107/Q108 failure
On 29/08/2023 18:54, Jonathan Burchmore
wrote:
On Tue, Aug 29, 2023 at 09:58 AM, Kees T wrote:
You measured the right point. It just shows that the
78M33 3.3V VDD output is getting slapped around a little by
several 2.2uF Tantalums on the board vs having a couple of 47uF
Tantalums at the processor. Surprising that all those 2.2uF
Tantalums on the board are apparently able to hold the 3.3V
level for the full 250ms until the SMPS comes ON.
I don't think LIN_REG_EN is turning "off" at 80ms--I think what
we're seeing is the handoff from the initial supply voltage
(through PWR_ON?) to the 3.3v signal from the processor PD7 once
it has booted up sufficiently. ?I seem to recall Hans discussing
this in his FDIM presentation.
It seems to be in a half way state at that time, The linear
supply FET Q102 is on and so is Q110 which provides a load for the
SMPS. But Q111 is also on so the power can come from the linear or
the SMPS - or go into the SMPS and the 47R load.
Then when the SMPS pulls VDD above the 3V which the linear can
supply the SMPS takes over and LIN_REG_EN is pulled low.
Three state logic, on, half on and off.?
Chris, G5CTH
Jonathan KN6LFB
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Re: QMX working FB then shorted out. Ideas?
I suppose it depends on how they failed... I have (had) mine in
sockets, so they're relatively easy to remove for troubleshooting.
Good Luck!
73, Paul -- AI7JR
On 8/28/23 17:03, Cliff wrote:
toggle quoted message
Show quoted text
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.
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
|
This group may be able to help.
They were where I got the idea of using
the hamlib file from an older version.
It fixed it for me but you do need to
be a bit computer literate to be able to juggle files from
different versions. They think this is OK, maybe you can
demonstrate why it isn't :)
Chris, G5CTH
On 29/08/2023 18:50, Karl via groups.io wrote:
toggle quoted message
Show quoted text
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
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Re: QMX - smoke - another C107/Q108 failure
On Tue, Aug 29, 2023 at 09:58 AM, Kees T wrote:
You measured the right point. It just shows that the 78M33 3.3V VDD output is getting slapped around a little by several 2.2uF Tantalums on the board vs having a couple of 47uF Tantalums at the processor. Surprising that all those 2.2uF Tantalums on the board are apparently able to hold the 3.3V level for the full 250ms until the SMPS comes ON.
I don't think LIN_REG_EN is turning "off" at 80ms--I think what we're seeing is the handoff from the initial supply voltage (through PWR_ON?) to the 3.3v signal from the processor PD7 once it has booted up sufficiently. ?I seem to recall Hans discussing this in his FDIM presentation. Jonathan KN6LFB
|
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
|
I used the ?QMX yesterday in what I call hybrid mode QMX TX, Web sdr for Rx works a treat if remaining on one frequency. ?Checked everything as far as I could but can't find any errors, even removed 401. Still completely deaf on all bands.
Paul DJ0CU G4ADF
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Re: QMX - smoke - another C107/Q108 failure
On Tue, Aug 29, 2023 at 09:45 AM, Kees T wrote:
That tells me that if you power ON again about 1-2 seconds after powering OFF, the 5V VCC rail is still at about 1.7V. Question is does the subsequent Power ON try to drive VCC above 5V ?
No, it did not appear to do so. ?If you look at my original scope traces you can see that VCC starts right around 1V because I had been turning the QMX on and off as I adjusted the scope trying to get a good view of things and it had not completely bled down. Jonathan KN6LFB
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Re: QMX working FB then shorted out. Ideas?
Found the part ok. $0.23 and shipping $7. <sigh>
Have to try to guess what other parts I many need to justify the shipping.
toggle quoted message
Show quoted text
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.
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.
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Re: QMX: Kit build trouble, a short between A & B for Step 17 of Section 2.9
According to the assembly manual it says "Finally, there should be NO connection between A and B. Hold one probe on any A point and the other probe on a B point. That should read infinite resistance (no continuity)." But my DMM measured 370 kilo Ohms between the ground (B) and the Q505/6. It is tricky to measure the resistance/continuity on such a tiny board.?
?
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Re: QMX working FB then shorted out. Ideas?
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.
toggle quoted message
Show quoted text
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.
|
Re: QMX - smoke - another C107/Q108 failure
On Tue, Aug 29, 2023 at 09:28 AM, Kees T wrote:
That LIN_REG_EN signal does not look right at all....it quits after about t=80ms.
It's possible I measured the wrong thing? ?I measured it from what I thought was pin 3 of the 3v3 SMPS board. ?The middle pin on the top. Jonathan KN6LFB
|
Hi Wayne,
To answer question 3… there is a better transistor for replacing the BS170’s - TN0606. The data sheet can be found here:
Note that the source and drain pins are reversed from the BS170 so you’d flip the TN0606 upside down (flat side against the washer). Others have made this substitution with excellent results. Again, it’s a good idea to place a very thin layer of thermal grease on both sides of the transistors to maximize heat transfer to the board.
Hope this helps!
Tony - AC9QY
Hey, all. First--I have been having a great time with my QDX. I've made numerous FT8 and JS8 contacts. I've even worked with other FSK modes with this little transmitter. I built mine for 9VDC input and I am seeing 5W on 80, 40, and 30 meters. I sometimes see between 5.3 and 5.6 on 40M. I am getting 3.8W on 20 meters.
So, Right when I was working an FT8 QSO, I heard what sounded like a crack sound from inside the QDX enclosure. Then, the smell. I knew then something went terribly wrong. I found the cracked BS170 as soon as I pulled the board out of the enclosure. I'm in the process of buying new BS170s. I know it is a TO-92 style, but I am seeing other variants of the transistor: D26Z, D74Z, etc. I have three questions:
1) Is there a specific BS170 I should get or will any of them work provided it's a TO-92?
2) Is there anything else I should do to prevent another BS170 fail?
3) Has anyone found an alternative to the BS170 that has less potential for failure?
Thanks,
Wayne KB4DSF
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Re: QMX - smoke - another C107/Q108 failure
It looks like about 38 seconds or so, if I'm measuring this right.
Jonathan KN6LFB
|
Re: QMX - smoke - another C107/Q108 failure
On Tue, Aug 29, 2023 at 08:29 AM, Kees T wrote:
1) What is happening to 3.3V between t=80ms and t=200ms after Power ON ? Need more detail on the actual voltage seen.?Maybe Jonathan can expand that area on the scope so you see more 3.3V. detail ?
Here's a tighter view: And zoomed in on the linear regulator portion. ?Vertical scale in both is 500mV/division with a -1.5V offset. Here's a similar trace with channel two showing LIN_REG_EN. ?Note the difference in scale and offset between the two channels. ?I didn't include VCC here because I don't have enough hands to hold the probes and not short anything out, sorry.
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Re: QMX substitute for Q103
I don't see why it should not work with the AOD21357. Specs are very similar to the AOD403 and both are well over dimensioned for this purpose. I would try it if I were in your shoes.
Experience is what you get if you don't get what you wanted! [unknown source]
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Re: #QMX holy smoke released again, C107 and D108 destroyed
#qmx
IF IT FITS and you want to use a premium cap, I would use the Kyocera?TPSE477K010R0050 for $2.58 at Digikey, qty 1.? It is 470uF 10% tolerance 50 milliohm ESR,? Not cheap, but this series is surge current tested 100%.? 2917 package (7343 metric), height = 0.169" (4.30mm)
- Steve K1RF
------ Original Message ------
From "Daniel Walter via groups.io" < nm3a@...> Date 8/26/2023 6:48:22 PM
Subject Re: [QRPLabs] #QMX holy smoke released again, C107 and D108 destroyed
Kees,
?I believe 470uF 10 V tantalums are also available in 7343, but are 1mm higher.?
--
73, Dan? NM3A
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Or put an absorptive bridge between the QxX and switch it in for tuning, then out to operate. Also don't let the tuner auto tune when it detects a change in SWR.?
--
73, Dan? NM3A
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Re: QMX - smoke - another C107/Q108 failure
The 1N4148 diode in series with the linear 3.3V output is a necessary evil to prevent backward current flow once the 3.3V SMPS rail comes up. However, it destabilizes the linear 3.3V rail as noted by the variation in voltage as the processor is executing its boot code. It is advisable to have a substantial capacitance on the processor’s power pins to minimize voltage. This should be at least 47uF - 100uF to ensure that the processor doesn’t experience an instantaneous dip below its minimum spec voltage which could cause the boot process to hang or go off into never-never land.
What happens on one unit is not representative of 1000’s of units so I hope the processor voltage during bootup is being tested on every unit prior to shipment.
Hi Jonathan, Kees
These plots supplied by Jonathan look completely normal to me.
The 3.3V rail experiences some disturbances during the boot-up process and this is completely normal; it is powered by the 78M33 linear regulator during that time via a 1N4148 diode. The diode voltage drop will naturally?show some variation depending on current draw, and current draw will be variable as the unit boots up various things.? On Mon, Aug 28, 2023 at 6:27?PM Jonathan Burchmore < burch@...> wrote: Kees,
Here you go.? Measured on my working 9v QMX.
On:
Turn off with encoder press:
Hard turn off (in this case turning off the bench power supply, not actually pulling the plug):
Hope this helps,
Jonathan KN6LFB
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Paul - AI7JR
Karl