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QMX plus - just did it in

 

... by supplying 30 Volts by mistake. :-(? .? ? It generated an ugly smell.? The QMX plus is now completely dead.? When opening the case I saw that a component next to the DC connector was cracked and deformed. I also smelt real bad and? is labeled "LG".? Whatl else might be damaged - or is it FUBB? In which case? I might have to order another kit.... (?)
73, Holger, Dk4LX
 

a component next to the DC connector was cracked and deformed.
Hello Holger,
I guess it's the over voltage protection element SMBJ13A. Your power supply delivered not only a high voltage but also a higher current I think.
?
Whatl else might be damaged?
Who knows, hard to say. You may remove the broken element, use a supply voltage of 7.5 V and a current limit to 0.25 A and try to switch on the QMX. Check the current
  1. after connected the voltage,
  2. when volume encoder is pressed and
  3. after releasing the volume encoder.
Which values do you see?
?
73 Ludwig
?
?
 

Holger --

You put 30V into a device rated for 12V or 9V?? What kind of miracle are you expecting?

Hope springs eternal, I guess.

-- 73 -- rec -- ad5dz --

On Sat, May 3, 2025 at 3:38?PM <DH8WN@...> wrote:
a component next to the DC connector was cracked and deformed.
Hello Holger,
I guess it's the over voltage protection element SMBJ13A. Your power supply delivered not only a high voltage but also a higher current I think.
?
Whatl else might be damaged?
Who knows, hard to say. You may remove the broken element, use a supply voltage of 7.5 V and a current limit to 0.25 A and try to switch on the QMX. Check the current
  1. after connected the voltage,
  2. when volume encoder is pressed and
  3. after releasing the volume encoder.
Which values do you see?
?
73 Ludwig
?
?
 

The voltage protection device died trying to save it?
?
Replacing it with a new part will tell how it did?
?
There is a long list of ¡®check before¡¯ items in electronics and?
Voltage?
Polarity
Necessary other items (eg antenna)?
Multimeter probe position and range
Attenuation / power levels?
PSU mode /current limit /settings?
?
etc?
?
I never leave the Lab PSU unconnected at higher than 3V
with 0.5A limit at end of a particular use
?
I never leave the multimeter set up for current
(Or 1 button wake up is a risky feature)?

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