Re: No output QCX 40 output drains show 1.6 watts in receive


Charles W. Powell
 

Start tracing your audio chain. You can use a screwdriver to “inject” hum into the op amp if you are careful not to short pins.   I have had several QCX units I have repaired that had a fault near IC8.  It’s worth checking.  You can figure out where you lose signal this way and separate an audio fault from something upstream.   You said you don’t HEAR the alignment tone, but did you get a meter peak when you adjusted C1?

73,

Charles

On Dec 10, 2019, at 6:58 PM, George Korper <georgekorper@...> wrote:

I understand with the voltage on the gate of the output transistor, it is consistent  with the output on the drain.
but is the IC3 bad? My electronics education is not deep enough to come up with it ( hi hi) Everything was working fine so at least I can rule out
bad soldering, but replacing the output transistors was stupid. I NOW HAVE LEARNED WHY YOU INSIST ON VOLTAGE MEASUREMENT FIRST. Thanks for being a good Elmer. 


On Tue, Dec 10, 2019 at 10:37 PM George Korper via Groups.Io <georgekorper=gmail.com@groups.io> wrote:
Alan,  I checked pin 3 again and it is still showing 5 volts. which I see shouldn't be 5 but zero.
The transmit voltages are not changed but the same as receive.


On Tue, Dec 10, 2019 at 5:30 PM George Korper via Groups.Io <georgekorper=gmail.com@groups.io> wrote:
I sent you receive voltages. Thanks for the link, I forgot to reread the trouble shooting section.
There was no change in voltages in transmit, so
I can see the 12 Volts is not on the pins in transmit.
In transmit nothing on the IC3 changes.


On Tue, Dec 10, 2019 at 4:59 PM George Korper via Groups.Io <georgekorper=gmail.com@groups.io> wrote:
IC3 Voltages LCD unplugged:
some values rounded off.
1) 5
2) 5
3) 5
4) .02
5) .01
6) 5
7) 0
8) 5
9) 0
10) 0
 11) 0
12) 5
13) 5
14) 5

On Tue, Dec 10, 2019 at 4:31 PM Alan G4ZFQ <alan4alan@...> wrote:
> I went ahead and replaced Q6. No change.

George,

Replacing things blindly may not work. It is not unusual for several
components to blow in the PA, replacing one component may blow it again.
Voltage readings are important. Also check voltages after you remove a
suspect but before you renew it.

> I will try to get voltages on IC3, but I didn't see the voltages listed
> in the list, are they somewhere else?

http://www.qrp-labs.com/qcx/qcxtrouble.html#transmit
> May I remove the LCD do get to to IC3 and still take the voltages?
Yes

> The QCX was running fine.......

Quite a story:-) Settle down do it slowly. Measure voltages, remove
anything suspect, measure voltages.. Report here.

73 Alan G4ZFQ










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