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So I received my QMX Kit last week, started to build it on Monday, finished it on tuesday.
I powered it up with current limiting lab power supply, this way I realized there was a short between left rotary encoder and DC socket.
After insulating it with 2 layers of tape, it behaved like expected:
0A when connected to power supply, 160mA when switched on.
I installed firmware, connected it to a dummy load (and oscilloscope) and tested if there was power out.
Power on 30m, Power on 20m, Power on 80m then I?m not sure anymore if it was 60m or 40m where it would draw high current immediately after keying and would not recover from that state.
I can only imagine it was because of a bad solder joint on one of the LPF coils, even though very unlikely (as it happened within fractions of a second after key down)
I already removed 4 BS170?s but the problem remains:
As soon as I switch it on, it draws high current and display stays off.
My lab power supplys current limitation probably prevented it from smoking...
So: Where to look for the short? I?m not too familiar with the switching power supply.
Any tips ?
73 Manuel; DL2MAN
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Manuel,
Something on one of the power supply boards is likely to be getting quite hot due to the excessive current! If you could find out which board has a hot component it would help greatly to narrow the scope of inquiry.
JZ KJ4A?
On Fri, Jul 28, 2023, 10:30 AM Manuel; DL2MAN < DL2MAN@...> wrote: So I received my QMX Kit last week, started to build it on Monday, finished it on tuesday.
I powered it up with current limiting lab power supply, this way I realized there was a short between left rotary encoder and DC socket.
After insulating it with 2 layers of tape, it behaved like expected:
0A when connected to power supply, 160mA when switched on.
I installed firmware, connected it to a dummy load (and oscilloscope) and tested if there was power out.
Power on 30m, Power on 20m, Power on 80m then I?m not sure anymore if it was 60m or 40m where it would draw high current immediately after keying and would not recover from that state.
I can only imagine it was because of a bad solder joint on one of the LPF coils, even though very unlikely (as it happened within fractions of a second after key down)
I already removed 4 BS170?s but the problem remains:
As soon as I switch it on, it draws high current and display stays off.
My lab power supplys current limitation probably prevented it from smoking...
So: Where to look for the short? I?m not too familiar with the switching power supply.
Any tips ?
73 Manuel; DL2MAN
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Hi JZ,
Thanks, that was a good hint and I should have come up myself with that....
In deed: L101 gets really hot
But I assume, that?s just a symptom for one of the surrounding semiconductors to have failed....
73 Manuel; DL2MAN
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I measure between 36 and 40 Ohms between VCC and GND with that PCB present.
Without that PCB it?s in the 600 Ohm Range....
So something on that PCB is pulling down VCC
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OK, after lifting a few components, it seems to be Zener Diode D108.
Without that Diode, low resistance between VCC and GND is gone....
Now looking to get replacement......
73 Manuel; DL2MAN
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OK, Manuel! It seems you have made great progress. I hope nothing more on the VCC distribution has been damaged. Your resistance check after pulling the damaged zener is encouraging.
The receiver chain from band switch mux and Tayloe detector, op amplifiers, and ADC all draw from VCC, as does the gate driver for the BS170s. If after replacement of the Zener a problem remains, turn the IR camera onto those devices.
Good luck OM!
73 JZ KJ4A?
On Fri, Jul 28, 2023, 6:33 PM Manuel; DL2MAN < DL2MAN@...> wrote: Hi JZ,
Thanks, that was a good hint and I should have come up myself with that....
In deed: L101 gets really hot
But I assume, that?s just a symptom for one of the surrounding semiconductors to have failed....
73 Manuel; DL2MAN
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Am I likely going to fry my, yet to be assembled, QMX since I don't have a fancy power source to?regulate voltage and current draw?? I only have a 12 v power supply that I use for HF rigs.? I plan on starting assembly this coming week.
Rob, W8MRL
On Fri, Jul 28, 2023 at 6:33?PM Manuel; DL2MAN < DL2MAN@...> wrote: Hi JZ,
Thanks, that was a good hint and I should have come up myself with that....
In deed: L101 gets really hot
But I assume, that?s just a symptom for one of the surrounding semiconductors to have failed....
73 Manuel; DL2MAN
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Rob,
It is wise to bring up any newly built device with caution and with the use of a current limited supply. You would do well to buy/make/borrow one.
JZ
Am I likely going to fry my, yet to be assembled, QMX since I don't have a fancy power source to?regulate voltage and current draw?? I only have a 12 v power supply that I use for HF rigs.? I plan on starting assembly this coming week.
Rob, W8MRL
On Fri, Jul 28, 2023 at 6:33?PM Manuel; DL2MAN < DL2MAN@...> wrote: Hi JZ,
Thanks, that was a good hint and I should have come up myself with that....
In deed: L101 gets really hot
But I assume, that?s just a symptom for one of the surrounding semiconductors to have failed....
73 Manuel; DL2MAN
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First thing to check is what the voltage out of that supply actually is.? Most supplies for HF radios sit around 13.8 V and that would likely be no bueno.
I think other people have mentioned using a 9V cell to test with.? That would be safer, but I'm sure someone with more experience than me will be able to answer in more detail.
Brock
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On 28/07/2023 23:09, Rob Lindsay wrote: Am I likely going to fry my, yet to be assembled, QMX since I don't have a fancy power source to?regulate voltage and current draw? Rob, A 30 Amp 13.8 volt (guessing) supply is a really bad idea. A voltage and current regulated supply is good. Bring the voltage and current up slowly. Any fault can usually be observed without total destruction. There are modules available that could be fed from a big supply. 73 Alan G4ZFQ
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Thanks for the input guys!? ? I just placed an order for a 300 watt variable voltage , variable amperage power supply.??
73, Rob W8MRL?
On 28/07/2023 23:09, Rob Lindsay wrote:
> Am I likely going to fry my, yet to be assembled, QMX since I don't have
> a fancy power source to?regulate voltage and current draw?
Rob,
A 30 Amp 13.8 volt (guessing) supply is a really bad idea.
A voltage and current regulated supply is good. Bring the voltage and
current up slowly. Any fault can usually be observed without total
destruction.
There are modules available that could be fed from a big supply.
73 Alan G4ZFQ
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I found this on eBay: 5A DC to DC Step
Down Buck Converter Constant Voltage or Current, 5-32V
And this describes it:
the article seems
quite positive. It has two multi turn trim pots, one to adjust the
voltage, the other to adjust the max current.
Just over ?6 for two.? Also ordered one
of those current/voltage meters.
Not as good as a full fat lab power
supply but better than a tired 9v PP3 battery.
Chris, G5CTH
On 29/07/2023 10:59, Rob Lindsay wrote:
toggle quoted message
Show quoted text
Thanks for the input guys!? ? I just placed an
order for a 300 watt variable voltage , variable amperage power
supply.??
73,
Rob W8MRL?
On
28/07/2023 23:09, Rob Lindsay wrote:
> Am I likely going to fry my, yet to be assembled, QMX
since I don't have
> a fancy power source to?regulate voltage and current
draw?
Rob,
A 30 Amp 13.8 volt (guessing) supply is a really bad idea.
A voltage and current regulated supply is good. Bring the
voltage and
current up slowly. Any fault can usually be observed without
total
destruction.
There are modules available that could be fed from a big
supply.
73 Alan G4ZFQ
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If you don't have a current limited supply, another option is just putting something like a 1A quick blow fuse on the 12V feed. Not as quick as current limit circuit but may save components from being "cooked". I used to do this before I had a proper bench supply. I went through a few fuses :-).
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Alan, a simple current limiter can be made using an LM317 voltage regulator as a current limiter. This application is in their data sheet paragraph 9.3.3. Here's a link to the circuit with a calculator for limiting resistor. -Steve K1RF
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------ Original Message ------ From "Alan G4ZFQ" <alan4alan@...> To [email protected]Date 7/29/2023 3:04:57 AM Subject Re: [QRPLabs] QMX died in first test run On 28/07/2023 23:09, Rob Lindsay wrote:
Am I likely going to fry my, yet to be assembled, QMX since I don't have a fancy power source to regulate voltage and current draw? Rob,
A 30 Amp 13.8 volt (guessing) supply is a really bad idea.
A voltage and current regulated supply is good. Bring the voltage and current up slowly. Any fault can usually be observed without total destruction.
There are modules available that could be fed from a big supply.
73 Alan G4ZFQ
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Chris,
Check it for transients before you start using it. It all sounds good, but if you have a few mSec at 12 V, you're going to fry it anyway.?
--
73, Dan? NM3A
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On 29/07/2023 13:32, Daniel Walter via groups.io wrote: Check it for transients before you start using it. It all sounds good, but if you have a few mSec at 12 V, you're going to fry it anyway. Dan Yes, a long time ago I made up a voltage/switched current limited supply from parts I had and data sheets. The only problem was the high voltage pulse at switch-on. I still use it and still remember the project it destroyed. I guess one day I will leave it connected to something.. 73 Alan G4ZFQ
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It is always safe to add a delayed relay to activate dc power output after powering on supply.
73
Barb WB2CBA
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Useful info, thanks guys.? Would
turning it on, then plugging it into the QMX help?
Chris
toggle quoted message
Show quoted text
It is always safe to add a delayed relay to activate dc power
output after powering on supply.
73
Barb WB2CBA
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OK, after lifting a few components, it seems to be Zener Diode D108.
Without that Diode, low resistance between VCC and GND is gone....
Now looking to get replacement......
OK Guys, D108 replaced with 5,1V Zener. BS170?s replaced (not because they were defective but because I initially unsodered them). Fixed a few solder joints, and QMX is in Service. Had first 2 CW QSOs tonight.... 73 Manuel; DL2MAN
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Manuel; DL2MAN
Rob Lindsay
GM0HUU Steve
Barb WB2CBA
Mike Besemer - WM4B