On Fri, Apr 4, 2025 at 11:11 AM, Matti OH6BEX wrote:
The QMX+ rev 3 does not start. With power button pressed, it takes 0.8 A current which slowly decreases to 0.5A.
0.8 A is to much.
Vcc and Vdd are around 0.1 V.
To start the controller you need Vdd at around 3 V. This voltage could be produced by IC101 but I guess there is a fault in the chain before. Pleas read
QMX QMX_plus Startup to find this chain.
Testing diodes with a DMM: D108 shows 0.17V and 0.2V, D109 shows 0.11V and 0.12V.
meaning that both diodes are damaged. But as the diodes are in-circuit, these values are probably meaningless.
A broken D109 is affecting Vdd.
Resistances:
...
These values are not so bad and affected by the broken diodes.
I also received some spare SMPS'es and installed those to the older QMX+ rev 1 which I broke by accidentally inserting faulty SPSM'es from another faulty QMX.
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Receiver works ok.
Diagnostics page is all OK except TX Voltage which is RED showing 10.4 volts (DC input is 12.2V).
I guess you destroyed the PA and because of high current Q507 was following the PA in dead. Please don't transmit with a broken Q507 and read
QMX QMX_plus PA problems, broken BS170 .
Apparently something in the TX chain is destroyed.
I have no oscilloscope. Is there something that I could check with an ordinary DMM?
Go to Terminal - Diagnostics (the controller will set a signal to switch off the PA voltage) and check voltage at D, G and S of Q507. If all values are nearly the same and high the Q507 should be broken. For more debugging check the Wiki page above.
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73 Ludwig
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