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I was prepping a QMX for loan to a friend in a nursing facility and foolishly used a wall wart labeled, 9 VDC @ 300 mA to power it as it only needed power for receive. I had opened the QMX to measure the voltage at the jack which read 15 V. Before I could pull the plug it died.
So what's the probable damaged part and how do I test it?
Thanks,
Reg
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Horse out of barn now but i am sure you will measure BEFORE next time!?
I have seen warts and usb adapters "go high" before and once ruined some consumer gizmo. I hink it has something to do with those aluminum can capacitors but not sure...
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73
Karl
KI4ZUQ
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On Tue, May 28, 2024 at 06:31 AM, Reginald Beardsley wrote:
So what's the probable damaged part and how do I test it?
With a bit of luck the power supplies.? Try checking them independently, there's some guidance in a file I put in the files area.? You need a current limited supply. And if you can get 3.3V into the main board you should be able to see if the main processor will work using PUTTY.
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Chris,
Thanks. Neither of the #1 boards shows 5 V on +12 after grounding power on. The voltage is 1-2 V max. Happily, I have two unbuilt QMX kits I can borrow replacements from.
Is Vcc = Vin? I've not seen it stated anywhere in the schematics.
Have Fun!,
Reg
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Hi Reg
I should make it clear, somewhere... - Vcc = 5V?
- Vdd = 3.3V
- Vin = the voltage right at the power connector input
- +12V = the voltage downstream of the reverse polarity protection and soft on/off power switch. Though identified as?+12V it could of course be other than that, depending on what your Vin is.
This Vcc/Vdd nomenclature appears to be most commonly associated with the 74-series logic in which on the 74xx and 74LSxx TTL (bipolar transistors) logic chips, Vcc was the supply voltage?(c = collector) and was always 5V. On the 74HCxx chips (MOSFETs), Vdd was the supply voltage (d = drain), and was not necessarily 3.3V; but the subsequent most common supply voltage on many digital IC's (MOSFET-based) is now 3.3V so this is what Vdd commonly means. It does all get a bit confusing and even controversial.?
On Wed, May 29, 2024 at 3:40?AM Reginald Beardsley via <pulaskite= [email protected]> wrote: Chris,
Thanks.? ? Neither of the #1? boards shows 5 V on +12? after grounding power on.? The voltage is 1-2 V max.? ?Happily, I have two unbuilt QMX kits I can borrow replacements from.
Is Vcc = Vin?? I've not seen it stated anywhere in the schematics.
Have Fun!,
Reg
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TI uses Vcc as a general designation for the supply voltage in the first edition of "The Integrated Circuits Catalog for Design Engineers" which for op amps is often a maximum rating of 18-22 V.
This appears in the catalog as "Supply Voltage Vcc" in the maximum and minimum ratings for parts. Don Lancaster always used +5 V for TTL logic part diagrams.
National (1976) used Vdd and Vss for supply and ground respectively. Motorola (1978) uses Vcc for the positive supply voltage. Signetics (1987) uses Vccs, Vccp, Vdd1, Vdd2, etc all in the same catalog.
I should add that there is no consistency from datasheet to datasheet in any of the catalogs V+ is as common as Vcc in the same catalog.
I think this is ample evidence that Vcc, Vdd, Vss are device specific and convey no information coming out of a PSU.
Based on that I assert that they mean nothing outside of the context of the device being used. A rail coming from a PSU tells you nothing about what it's driving. So properly the voltages should be stated. If the +12 tracks V-IN it should have (V_IN) in parentheses
Have Fun!
Reg.
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FYI: This device allows one to adjust the voltage (down only) and clean the power coming from various wall warts or computer power supplies. However, the output voltage will be at minimum 2V lower than the input voltage to the device.
see:
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73
de Roy - KI0ER
Littleton, Colorado USA
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This is why I prefer supply nomenclature on schematics be specific such as 3V3 and 5V rather than Vcc and Vdd which are too easily confused.
On Tue, May 28, 2024 at 11:29?PM Hans Summers via <hans.summers= [email protected]> wrote: Hi Reg
I should make it clear, somewhere... - Vcc = 5V
- Vdd = 3.3V
- Vin = the voltage right at the power connector input
- +12V = the voltage downstream of the reverse polarity protection and soft on/off power switch. Though identified as?+12V it could of course be other than that, depending on what your Vin is.
This Vcc/Vdd nomenclature appears to be most commonly associated with the 74-series logic in which on the 74xx and 74LSxx TTL (bipolar transistors) logic chips, Vcc was the supply voltage?(c = collector) and was always 5V. On the 74HCxx chips (MOSFETs), Vdd was the supply voltage (d = drain), and was not necessarily 3.3V; but the subsequent most common supply voltage on many digital IC's (MOSFET-based) is now 3.3V so this is what Vdd commonly means. It does all get a bit confusing and even controversial.?
On Wed, May 29, 2024 at 3:40?AM Reginald Beardsley via <pulaskite= [email protected]> wrote: Chris,
Thanks.? ? Neither of the #1? boards shows 5 V on +12? after grounding power on.? The voltage is 1-2 V max.? ?Happily, I have two unbuilt QMX kits I can borrow replacements from.
Is Vcc = Vin?? I've not seen it stated anywhere in the schematics.
Have Fun!,
Reg
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I've got plenty of buck convertors. I was trying to complete the project while getting ready to go to FDIM and do a talk. A perfect example of the folly of "multitasking". You make more mistakes :-(
Reg
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I've considered this a great deal. I think that an LM317 to protect the input would work well. It will slap 40 V down to 12 V so it should be able to protect the QMX from anything remotely plausible and they are small , cheap, and require few other parts.
Use a comparator to switch the LM317 in or out if Vin is <= 12 V and accept the voltage drop if Vin greater.
Have Fun!
Reg
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Hi Reg
An LM317 is a linear regulator and it will dissipate the extra voltage as HEAT. If you did apply 40V and it slapped it down to 12V that would be 28W of heat dissipation. There aren't any LM317 variants which can cope with that degree of abuse, even if you had a heatsink big enough (the thermal resistance of the case is too high). I realize 40V is an extreme scenario though...?
73 Hans G0UPL
http://qrp-labs.com
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I'm going to load test a bunch of random wall warts. It's very tempting to repurpose them, but they appear to only provide the rated voltage at close to the rated current (load). So they really need a buck convertor to limit the voltage to the stated level.
Have Fun!
Reg
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Whenever I repurpose wall warts, I do it by putting an LM713 supply on the output, or I cut open the case and solder the transformer into a homebrew supply.? LM7805 or LM7812 are good, and require fewer added components than an LM317. ??
73 Jim N6OTQ
On Thu, May 30, 2024 at 8:54?AM Reginald Beardsley via <pulaskite= [email protected]> wrote: I'm going to load test a bunch of random wall warts.? It's very tempting to repurpose them, but they appear to only provide the rated voltage at close to the rated current (load).? So they really need a buck convertor to limit the voltage to the stated level.
Have Fun!
Reg
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On Thu, May 30, 2024 at 12:07 PM, Jim Strohm wrote:
LM7805 or LM7812 are good, and require fewer added components than an LM317. ??
7809s are suitable for 9-built? QRP-Labs radios. 73, Don N2VGU
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I always use what I got.? The old NatSemi databook gave instructions on how to repurpose nearly any LM regulator?chip to any voltage.? I think it required a 3V drop, but don't quote me.? I'll try to find my copy of NatSemi (or was it TI?) and see if my scanner still works.
73 Jim N6OTQ
On Thu, May 30, 2024 at 11:23?AM Donald S Brant Jr via <dsbrantjr= [email protected]> wrote: On Thu, May 30, 2024 at 12:07 PM, Jim Strohm wrote:
LM7805 or LM7812 are good, and require fewer added components than an LM317. ??
7809s are suitable for 9-built? QRP-Labs radios.
73, Don N2VGU
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National and it's a 3 V drop.
I'd like to note I was NOT suggesting using it as a voltage regulator as it dissipates too much heat, but as a protective device to trigger shutdown.
What I'm seeking is the voltage equivalent of a fuse.
Have Fun!
Reg
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Reg? what you need? is the MC 3423? which is specifically designed to fire? an? SCR if it sees over voltage.? It's put downstream
of any regulator with? a fuse upstream of regulator.? The BT152? scr is known compatible.? There are? sensistive gate and non sens gate? ? SCRS so don't substitute.? ?THe? MC 3423? is? voltage set by? a? potentiometer across the line? it is? set to protect .? ?It is presumably
highly accepting of supply v? variations to? its own electronics as it does not? require? a separate? transformer winding?
and? PSU just for its own use.? ? It's likely? good to about? 40 V dc.? See chapter 7 of the Arrl? HB 2014 or? 2015? to see how it is
implemented if above? description is inadequate.? ? You will likely have to search old analogue parts places like futurelec.com to find same.? The MC part requires one decoupling? capacitor.? Clearly something that? has been tested in a professional design house? is likely to? drop in? and work without? issues.? ? THere is no output triggered? indication of course . I guess in? professional settings? there might be two fuses installed? in series? the? slightly larger one for the SCR? to pull to GND an blow and a smaller one for normal output protection.??
TEF
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Instead of turning an SCR on to crowbar the output and blow a fuse, why not open a MOSFET switch supplying the power to the downstream side?
Nothing to replace. Just remove excess voltage source.
*Nothing* is a "drop in" in a QMX. It's very cramped in there.
Have Fun!
Reg
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OK, I finally got around to addressing this. The SMPSes in both QMXs were destroyed. In addition, the main board on one was also damaged and does not boot. Thankfully, one appears to have survived with SMPS replacements from the unbuilt kits I had on hand.
I used two different wall warts. A 9 VDC and a 12 VDC. Both put out ~17 VDC open circuit. I "knew" this in a general sense, but in my haste didn't realize that 12 V was the damage limit.
From an engineering viewpoint I have to call this a serious design FAIL by Hans in what is otherwise the best design on the market. Connection of a common wall wart of specified or lower voltage, sufficient current and correct polarity should NOT destroy the radio.
I personally can't understand why the SMPSes in the QMX shouldn't withstand at least 24 V input. I'd prefer that any voltage and current above minimums and below 24 VDC would operate the radio. That said, it has a cost. A Zener, LED and MOSFET to cut off power if the input is over voltage is cheaper. It just precludes recycling wall warts to power the QMX. It does prevent damage.
And yes, Hans, I know you're swamped by the QMX+ ;-) So, I quite understand this might take a while to address. But destroying the radio by wall wart is not acceptable.
Have Fun!
Reg
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Id say its a wall wart fail. I never found a single unit of that type that has output voltage as writen on the label.
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Karl
Donald S Brant Jr
Timothy Fidler
Ivica - YU1QRP