Re: QMX - smoke - another C107/Q108 failure
Hello Hans and Jonathan,
The plots require some questions to be answered in my mind.?
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 ?
3) Both the 5V VCC and 3.3V VDD have a 470uF capacitor across the voltage outputs for voltage level stability, When the 78M33 Linear Regulator is being used it has ONLY a 2.2uF capacitor across the voltage output. Is that sufficient for voltage stability until the 3.3V SMPS is enabled ? .....or should it be larger to handle the initial power fluctuations during startup.
4) After 250ms and the 3.3V SMPS is turned ON, is the 78M33 Linear Regulator really turned OFF ??
Hans, I agree completely with not using the LTM8078 for the reasons you gave.
73 Kees K5BCQ
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CAT port returns ` ` ` on QCXmini
Just curious if anyone has seen this and might know what's going on.? Using Putty on the CAT port of a QCX-Mini, the QCX returns a (`) with each character typed.? ?For example, if I type FA; and then ENTER, it returns a ` with each character typed.? I have Putty set to 38400 8,N,1.? I can't remember what flow control was set to but it appears from the manual that it doesn't matter.? The USB to RS232 cable that I'm using outputs 6 volts (unloaded) which I assumed is close enough to TTL level so as not to harm the unit. (did I assume correctly?)? I reversed the tip and ring just to make sure I had it connected correctly and no characters are returned.? I also connected tip and ring together for a loop-back test and characters that I type are returned on the screen on Putty.??
This followed a catastrophic accident just as I finished construction where I dropped a metallic object onto the top of the unit on the pins that connect the LCD to the Micro-Processor.? I replaced the Micro-processor with a new one from QRP Labs.? The LCD only shows only blank (black) characters after the accident.? I have a replacement display on order.? According to the manual, the LCD shares 2 of those pins with the CAT port.
I have verified that VFO tuning works by following the signal on a spectrum analyzer as I tune the frequency by wrapping a wire around the unit to use as an antenna for the spectrum analyzer.??
Thanks, Jerry AC5JM
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Re: QDX rev 5 Troubleshooting
First, it is considered good form always to post your name and call at the end of a post.? Then, others can direct their posts to the correct person.? Also, when posting in response, direct the post to the person you are responding to.
To the original poster:
The QDX has gone through 5 revisions of the circuit board.? The differences can impact the usefulness of the help from the forum.? Please post the board revision and the model to help us give you the best information.
To answer your question on how the LPF selection works, there is a detailed description in the construction manual on page 73 for the Rev 5 board.? Others will be around the same page with the same heading.? You can get the correct manual from the QRP-Labs QDX web page:
Basing the selection diodes forward in a simplified description connects the two leads like a switch.? Reverse bias opens the switch.? The caveat is that the RF peak voltage must not exceed the reverse bias voltage, or the diode will conduct.? ? For receive, that is in the millivolts, and the 5-volt supply is enough.? When transmitting, the voltage can get over 45 volts peak to peak or 23 volts peak.? That means the reverse voltage on the diode must be above 24 volts for safety.? There is no 24-volt DC supply in the QDX, so Hans developed a voltage doubler circuit for transmitting.? That doubler is D8 and D9 with capacitor C27.? This happens only when transmitting and does require a good RF output.? If there is no RF, The doubler does not work, and D7 provides the input voltage supplied to the QDX until the doubler kicks in.
The supply to forward bias the LPF diodes is different for different boards.? The original board (Rev 1) used the input voltage through a MOSFET switch and then a resistor to bias the selected diodes forward.? The same circuit was used up to Rev 4 when Hans came up with using the processor to act as the controller for a switching buck regulator to reduce the power dissipation required by the series resistors.? There are other aspects of the new design that benefited the QDX operation.? This is an example of why it is important to list the board revision when asking for help.
To address how to verify that the LPF selection is working, first, confirm in receive mode that only two of the diodes (the two that select the band) have the band (cathode) close to zero volts.? The other four should be at 5 volts.? That would verify that the selection process is working.? At that point, you should be able to receive and decode digital signals with the QDX.
To test in transmit, first verify that there is DC over 15 volts (this would depend on the voltage supplied) on C27.? As in the receive selection test, verify that only two diodes are at zero volts DC and the others are close to the voltage measured on C27.
There is a diagnosing help page on the QRP-Labs web pages:
I? hope that the above helps.? Good luck in finding the issue.
73
Evan
AC9TU
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Wayne,
Thanks for the reply!?
Read over other posts here about use of auto-tuners and the Q-Line. In some cases they'll show a momentary high VSWR to your rig. The PA in QCX-QDX-QMX doesn't like too high a VSWR and could stress one or more BS-170s leading to a failure.
The "Tayloe/LED/SWR-bridge" at least will give you a fighting chance.
Welcome to the club!
--Al
WD4AH
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Picture of a 4sqrp tuner...
--
73
Karl
KI4ZUQ
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Re: QMX working FB then shorted out. Ideas?
Steven,
Thanks so much for the response. I'll get to it and respond when I know more. I've a lot to learn here.
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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: QDX rev 5 Troubleshooting
Thanks again John and Nick,
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Managed to get some more PD time.
I disconnected the cat on D3 and D6 to see if that told me anything but I don’t think it it did, results below, look like the only delta is D3 and D6 stay at 5v on TX, but I guess that’s because LPF3 is not disconnected.
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D3 & D6 Cat disconnected
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On RX
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On TX
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Diode cat
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80m
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40m
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20m
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Diode cat
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80m
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40m
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20m
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D1
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0
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5v DC
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5v DC
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D1
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5v AC
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5v DC
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5v DC
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D2
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5v DC
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0
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5v DC
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D2
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5v DC
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5v AC
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5v DC
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D3
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0
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0
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5v DC
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D3
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5v AC
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5v DC
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5v DC
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D4
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0
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5v DC
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5v DC
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D4
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5v DC
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5v DC
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5v DC
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D5
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5v DC
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0
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5v DC
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D5
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5v DC
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5v AC
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5v DC
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D6
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0
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0
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5v DC
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D6
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5v DC
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5v DC
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5v DC
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?
Still the big delta on TX remains. TBH I don’t really understanbd how the circute works, bit, sure but the whole soup to nuts is stilkl beyond me so I’m taking your advice and interpreting it as best I can. I’ve started looking at T1 to see what that tells me:
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T1
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40m
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20m
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RX
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TX
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RX
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TX
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2 tap coil (one is ground)
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0
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6v AC
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0
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2v AC
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3 tap coil top (Q8/10)
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5v DC
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3.6v DC +1.7mV AC
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5v DC
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4v DC +0.6V AC
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3 tap coil mid (L14)
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5v DC
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5v DC
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5v DC
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5v DC
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3 tap coil bottom (Q9/11)
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5v DC
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3.6v DC +1.7mV AC
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5v DC
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4v DC +0.6V AC
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Now I’m really confused!!
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A QDX which w1NC did over for me.? Thanks.? I will be back later this afternoon.
HIF
On August 29, 2023, at 2:49 AM, Ronan Cantwell <ronancantwell@...> wrote: On Mon, Aug 28, 2023 at 01:06 PM, Leland Lannoye, W9HIF wrote:
I have a weird problem. No waterfall. The rig goes through normal fire up. Don't know if there is output or not. I use my tablet, ft8cn and an end fed log wire and am on 7.074 mHz.
Leland!? I noticed you corrected Billy (N5SE) on his grammar/spelling. You might want to run your own posts through the same quality control.? ? Just jesting..... To which rig are you referring?
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Hey, Al, but I will admit, it's not one specific for QRP. It's my shack's auto tuner. That might not be the best choice.
Wayne
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Hey, Roger. I've not noticed any SWR fluctuations, but you bring up a good point. I might have to watch that more closely when I repair the radio.
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Wayne,
Are you using any kind of antenna tuner?
I think using a manual tuner with a switchable SWR indicator is a good way to prevent future BS170 failures.
Good luck with the repairs!
--Al
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Hi Wayne.
And was the failure also on 40? That sounds like there is something intermittent maybe, on your 40m antenna. So the SWR will also be fluctuating...not good!
Roger
8P6RX
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On 29/08/2023 07:55, Wayne Greene wrote: I sometimes see between 5.3 and 5.6 on 40M.
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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: VFO signal generator frequency limits
And Richard, to your question:
If you dial a frequency bellow 3.3 kHz or over 570 MHz you get an "E" symbol on the LCD.
73 Bojan S53DZ
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Re: VFO signal generator frequency limits
Hi,
my experience with the QRP Labs VFO/SigGen is different. The chip is M5351A.
It works well from 3.3 kHz to 310 MHz.
Since it gives out a square wave signal we can not easily see the power level.
The level at 50 MHz was around +15 dBm, at 310 MHz the level was still over +10 dBm.
The power was measured without output LPFs, so inherent all harmonics. At 50 Ohm load.
Since the output is RF with a DC bias I used a decoupling C followed by a 20 dB 50 Ohm attenuator. All SMA.
At lower frequencies the frequency was measured directly at the TTL (DC) counter input.?
73 Bojan S53DZ
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I bought one of the ATU10 tuners. I was a little underwhelmed at first, but later firmware releases made it an excellent portable tuner. Darn close to the Elecraft tuner, IMHO.
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Re: QMX - smoke - another C107/Q108 failure
It's a great part, other than the fact that it cost $12.80 for a tray of 1000, (About $20 per part in smaller quantities), is a single sourced part with no replacements if it becomes unavailable, and it's a ball grid array package, making it totally impossible for a purchaser of the QMX to ever replace it.??
-Steve K1RF
------ Original Message ------
Date 8/29/2023 12:08:18 AM
Subject Re: [QRPLabs] QMX - smoke - another C107/Q108 failure
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.
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Re: Blue screen of death U3s
As an update I think I've found the issue.?
Replaced the screen, no change, replaced the ocxo with a bog standard si5351 synth board, still not working but I have garbage on the screen, so progress but still not working. Listened for 20MHz crystal, all good, listened for the 27MHz crystal, nothing.?
So I think that the problem was a damaged ocxo board followed by a non functioning crystal in the replacement synth board. 2 separate problems at different times but in the same repair. I'll pull the crystal later and order a replacement.?
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.
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20% is a typical tolerance and if you have an inductance meter it’s better to go back to the theory calculated inductance values and check them as you wind?
(That said it’s common to see ‘off values’ result ?in practice for output (LPF) filters as they are tweaked to provide matching as well as filtering )
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Re: QMX - smoke - another C107/Q108 failure
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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Karl
Leland Lannoye, W9HIF
K9NUD-Steve
M0RON
Bruce Akhurst