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Re: BS170 Fail
Hi Wayne.
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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 On 29/08/2023 07:55, Wayne Greene wrote:
I sometimes see between 5.3 and 5.6 on 40M. |
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BS170 Fail
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
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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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 ------
From "Stephan Ahonen KE0WVA" <stephan.ahonen@...>
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.? 73 Hans G0UPL On Mon, Aug 28, 2023 at 6:27?PM Jonathan Burchmore <burch@...> wrote: Kees, |
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Re: QMX - smoke - another C107/Q108 failure
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 |
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Successful QMX build - and some bug reports
#qmx
开云体育Dear all, ? many posts discuss issues with the QMX build (shorts and holy smoke) and as reader one may get the impression this is normal. Well, I just want to share a successful build story. It was my second kit after a QCX-mini earlier this year, so I would not consider myself a very experienced builder. ?? Overall I had no build issues, got good RF sweeps and between 3.5 to 4 W power output on all bands “as is” – no toroid fiddling (12V build). I see around 150mA current draw when switched on and receiving (backlight on). Several FT8 contacts done on 40-30-20. Below the reports on 30m this morning (~30 minutes operation using a pre-tuned random wire): ? ? ? @Hans: Some bugs I observed so far: ? In Digi mode (FT8):
? In CW Mode (actually what I want to use the QMX for): Audio issues:
? CW Settings:
? Otherwise I’m eagerly waiting for:
? Thanks Hans for this nice kit! Matt ? |
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When previously using iron-powder toroids I've always had close correlation between measured inductance values and those obtained from the published tables and on-line calculators. So when doing some development of a [40m/30m] LPF for my QMX I was surprised to measure inductance differences between 10% and 20%.? For example the calculator at toroids.com shows 440nH for an 11-turn coil on a T30-6 core with 25mm pig-tails. But with the T30-6 supplied with my kit I'm measuring 529nH with pig-tails of just 10mm. It's the biggest discrepancy I have ever seen. It's not a problem for a one-off design checked on the bench. But if this is typical then there may be consequences for production repeatability of LPFs, especially any that use a "notch" to pull down the response at second harmonics. Has anyone else measured similar discrepancies?
(I'm a 30+ year professional user of VNAs and am freshly calibrated at the measurement reference plane with SMA short, open & load. And I am counting the turns by the number of passes throught the toroid centre.) |
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Re: A weird problem
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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QDX Rev 4 Only Shows 80M Band After Working Near T2
After doing some rework on T2 my QDX it only shows 80M in the band config, the other bands do not appear at all. Normally there would be 80,60,40,30,20 with a whole set of options for each but I only see 80M.
I happened to reflash to an older 1_05 firmware and the bands all show up when running that version but disappear again on 1_10. I have done a factory reset with no change. The diodes all go to 0.6-0.7v for the corresponding bands when I test them on 1_05. I'm guessing I did something to an SMT component around T2. The parts are very cheap but I'd like to know what one(s) might be involved and I don't want to attempt to repair something if the fault is elsewhere. I've read through the documentation and I didn't find any mention of band detection/enable aside from the jumper wire if it was a high band model (mine is not) Does anyone know what components or connections would make a Rev 4 QDX only show 80M on 1_10 but be ignored on 1_05? |
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Re: QMX: Kit build trouble, a short between A & B for Step 17 of Section 2.9
370 kOhm as in kilo-ohm? That's the opposite of a short. Installed in the circuit, there is about 10k of resistance between the primary and secondary windings of T501 because the primary is connected to ground through R508/9 and R525/6, and the secondary is connected to ground directly. This is the peril of trying to measure any component in circuit, because you're not just measuring the component, you're measuring the circuit around it too.
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Re: QMX working FB then shorted out. Ideas?
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. |
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Re: QMX working FB then shorted out. Ideas?
开云体育Well, pulled the finals and still draws 700mA when the left encoder is pushed. It stays there until I kill the power to it. No display backlight.Other things to check? I hate to pull the driver chip with out good evidence of a problem. Is there a way to check things further? 73, Cliff, AE5ZA
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Re: 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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K9NUD-Steve
M0RON
Bruce Akhurst