Re: QMX HW Diagnostics: No TX?
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Hans, thanks! I will remember that.
JZ
Hi JZ
An important note about this... You are right that there's a setting to keep the PA modulator high during RX. However: when the diagnostics screen is open, the PA modulator voltage is always low on RX, regardless of the normal setting. Therefore if one sees a high PA voltage in the diagnostics screen when not keying the transmitter, which will be coloured red, it does always indicate an issue with the PA modulator.?
73 Hans G0UPL
Todd,
In FW rev 1_00_011 a feature was added to enable the TX voltage (in RX)? to be set well above zero. (3a: Mod high in RX).
?Leaving it at zero was creating undesired capacitive loading of the RX path and potential diode-induced IMD as well. Restoring some voltage at the drains of the BS170s solves that problem.
Check to see if you have that option enabled on your QMX.
If not, and if you still have voltage showing in RX, there may be a hardware problem with the modulator circuit.
JZ KJ4A?
On Mon, Jan 1, 2024, 3:11?PM Todd W2TEF < w2tef@...> wrote: Hmmm... my diodes look like they're correctly oriented. I can't locate any evidence of damage or shorts to any components, particularly around the toroids and inductors. I'm absolutely willing to take another swing at the toroids if they're suspect. But I feel like the diagnostic screen gave me a clear pointer toward a problem:
 
When transmitting, the voltage is at 10.1v (and output of 0 watts!). The operation manual states (p. 73, v.014):
Additionally, the PA voltage is measured,
after the RF envelope shaping (amplitude modulation). In transmit, this should be a little less than
the supply voltage measurement. In receive, it should be near to zero volts. The PA voltage is
coloured green or red depending on whether it is within a reasonable operating range or not."
But in receive, it's still at 10.1v. I see other images in the forum showing that value at, e.g., 0.6v at receive.
Where is this reading being taken? Perhaps I need to look "near" there in the circuit for a nicked wire or a solder whisker??
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