>> So I started on the Receiver Signal Tracing in my manual. Everything
>> was more or less correct until I got to the crystal filter:
>>
>> 4. Post-Mixer Amp Output. Expected 2.2Vrms. Got 3.02Vrms
>>
>> 5. -5dB Pad Output. Expected 1.40Vrms. Got 3.04Vrms
>>
>> 6. Crystal Filter Output. Expected 0.35Vrms. Actual 0.094Vrms.
>>
>> I stopped there, because this seems very wrong.
DolfinDon suggested:
> If you are losing the signal out of the crystal filter check each crystal
> pin to ground with an ohm meter. You should get a high reading not a short.
> Sometimes if too much solder is used the solder will flow up under the
> crystal shorting it to the ground plain on the top of the board under the
> crystal. If one of them is shorted you will need to remove that crystal and
> remove the excess solder.
Nope, it's not a shorted crystal; all pins measure 'infinite'
resistance to ground.
I measured each pin with the RF probe. Here's what I get, which
doesn't make a lot of sense to me (this is viewed from the bottom
of the board):
3.16v (in)
X7 1.1 3.16
X8 1.0 1.1
X9 0.58 1.0
X10 0.78 0.58
X11 0.48 0.78
These are "rough" measurements - neither the radio nor the signal
generator had been warmed up when I took them just before going to
work, but the relative values are about right.
There's no drop at the -5dB pad because I have removed a KNB2 and
jumpered 1-6 on the connector; the pad itself is 'gone'.
Should there really be such a big drop across any of the crystals? And
why would the voltage go back up?
(And should I be concerned that the crystals are marked 4.9136-S instead
of 4915-20?)
I notice, now that I look at them again, that the output measurement
is not very far from the 0.35V that's expected. There's a diode (D34)
between the last crystal pin and the jumper W3, perhaps that's the problem?
73,
chris
_______________________________________________
Elecraft mailing list
Post to: Elecraft@mailman.qth.net
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
