开云体育

ctrl + shift + ? for shortcuts
© 2025 开云体育
  1. QRPLabs
  2. Topics

QMX+ rev. 1 Crowbarred PA #amperage #magicsmoke #problem #bullshit #q507

 

On Mon, Jan 13, 2025 at 03:55 PM, Damon wrote:
The new PA’s were placed and I powered up again with 12v and current limited to 250mA.?
On the display, I have a blinking “6” low voltage alarm.?
Damon, blinking "6" only in TX mode or also in RX mode before try to TX or after try to TX? For TX mode 250 mA is much to low and the power supply will hit the limit. When the power supply is going below 6 V the QMX is disabling the PA, the current is below 250 mA again and the voltage comes up to the value from before. (Such a fast down and up of the supply voltage is dangerous for the QMX.)
12V rail at 6.68Vdc
How much external voltage?
6.68 V in which mode (TX, RX)?
Good VFO clock output from CLK0 & CLK1 into IC503.?
I guess you mean IC403.
Good and expected values shown from IC’s 501-503.
Like described in QMX QMX_plus PA problems, broken BS170? With or without BS170?
PA’s dropping 980mV as measured at T501.
Dropping in which way?
980 mV DC or AC rms or AC pp or what?
Measured at which point of T501.
What is your oscilloscope showing at the drains of the BS170 (AC and DC, RX mode and TX mode)?
?
73 Ludwig
 

Damon,
?
You previously said:
?
" After replacement of all, I left off the PA’s and the radio powered up fine. All RX alignments were completed satisfactorily and performance is impressive.?
? The new PA’s were placed and I powered up again with 12v and current limited to 250mA.? ?On the display, I have a blinking “6” low voltage alarm. Today’s results probing with my oscope:? 12V rail at 6.68Vdc"
?
So the receiver works fine without the BS170's installed,
but once you install the BS170's your? power supply goes into current limit, dropping to 6.68 Vdc?
?
The final will be getting 12v from the power supply during receive (I forget why, but there's a good reason for this).
However, the gates of all BS170's should be at 0 volts when receiving, and so the BS170's are not conducting.
I don't understand how installing the BS170's would cause the rig to pull so much power.
Verify that the gates are 0 Volts (you can do this without installing the BS170's just check the gate pads).
?
There could easily be a short in T501 that could suck the power supply down like that.?
But I don't see how removing the BS170's would make such a short go away unless the gates are not at 0 Volts.
?
When you say "it drops about 4.3 Vdc", does that mean your power supply
is now at 12v - 4.3Vdc = 7.7 Vdc??
Previous measurements was 6.68 Vdc, but that difference could just be due to a change in part temperatures.
?
You say "No signals present on IC403 other than Vcc, Vdd."
If the receiver is operating correctly, then CLK0 and CLK1 must be present at pins 2 and 19 of IC403.
They will be within a few KHz of the receive frequency on the dial, and are 90 degrees out of phase.
?
Jerry, KE7ER
?
?
?
?
On Mon, Jan 13, 2025 at 08:00 AM, Damon wrote:

I have my power supply set for 12.00Vdc and current limited to 250mA. The radio is being tested in RX only and with PA’s installed at this point. When the radio is powered on, it drops about 4.3Vdc as indicated on the supply display and my DMM/o scope. This is measured on all points of the 12V rail within the radio.
?
Good VFO CLK0&1 signals on IC204. No signals present on IC403 other than Vcc, Vdd.
I have not yet tried to take any measurements in TX mode yet. As for T501, I was not clear… In RX, I read 900mV from T501 into the PA’s, 0V at the gates.

?
 

Your fault finding approach is not really going to work. ?
You seem to be using the scope for supposedly precise DC readings and not providing the correct power supplies to get meaningful results anyway
?
Personally, from where you are, I’d remove all your BS170s and do full voltage and resistance checks to /from the Drain connections.
?
Also look hard at the waveforms on the gates?
?
?
?
?

1 - 3 of 3