From: Charlos Potma (Charlos.Potma@rivm.nl)
Yesterday I finished building and aligning the OHR Classic.
Stuffing the boards went ok, although (see earlier message) I
think the soldering surfaces on the oscillator and receiver
boards are a bit small due to a solder mask alignment error.
However, after connecting a (windom) antenna to the classic
I was hearing nothing but a roaring sound. It seemed completely
overloaded. After inserting a 20dB attenuator in the antenna
circuit it was better but the receiver still sounded rather 'rough'.
After making some measurements I discovered the AGC was not
working. Voltage on pin 5 of U200 (MC1350) was a constant 4.8
Volts. Futher measurements showed that U207 (NE5534) was not
producing any output. Pin 2 of this IC was at 0 Volts and it stayed
that way even after removing U207 ! After a lot of headscratching
I decided to remove the U207 IC socket. As the documentation
promised this was rather painfull: I had to cut the socket in half
and had to remove each half by heating the pins and wriggling it
out of the board. Once the socket was removed I saw that pin 2
was shorted to the component screen side of the board by a tiny
amount of solder that was sucked up into the hole. Indeed the spacing
between solder surface and screen is a bit small here...
Anyway, after correcting this fault and putting a new socket in
I found the AGC still not functioning, although voltage on pin 5
of U200 was now going up a little with signal strength.
QUESTION: could someone with a classic (maybe Daniel before he
sells his one off :-) ) measure the voltage on pin 5 of U200 with
and without a signal present ? What is the normal voltage swing to
expect here with a MC1350 ?
SECOND QUESTION:I think I will need to be able to switch off the
preamp, especially on 40m. (*). Has anyone done this ? Has anyone
recommendations to do this ?
Once I can solve these problems I think I will have a great little
rig. I like the QSK as well as the ability to adjust the output.
(*) The only receiver I have that 'behaves well' on 40 is my
old Drake R4C.
73, PA3CKR, Charlos Potma
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