Uniden 300 distorted RX audio help needed
barett
I have an Uniden 300 homebase with a receive Audio problem. The audio
distorts. It sounds load enough but is very rough sounding around the edges.
Has anyone got any ideas on what could be causing this problem?
Many thanks
Peter
Did you get it that way or has it suddenly started sounding crap?
Several possibilities, including:
Knackered speaker.
Incorrectly tuned quad coil.
Wrong IF filter fitted.
Faulty audio IC.
If you have a spare (known good) speaker, then you can plug
it in to check if the internal one is faulty.
Other that that, fixing it will require appropriate test equipment
and electronic fualt finding knowledge. If you don't have these,
find someone who does.
Peter.
barett
"Peter" <pe...@peter.invalid> wrote in message
news:gurss5$h81$1...@news.ett.com.ua...
Hi Peter
Changed the speaker. That helped a little.
Retuned L4. That helped a lot.
Correct IF filter fitted.
Got no way of checking the audio IC.
Still not quit right, but 80% better than what it was.
Got any other things I can try?
Thanks
barett
"barett" <bar...@blueyounder.co.uk> wrote in message
news:_5VQl.55632$qP7....@newsfe04.ams2...
Forgot to mention. When I purchased the radio it was already like this.
Peter
>
> When I purchased the radio it was already like this.
>
Being more careful where you buy radios from?
:~)
But seriously...
I am not sure which board you have, I am looking at the 034
and 039 diagrams. L4 would appear to be first IF, the quad
coil is L19. Quad coil will be next to the FM IC, uPC1028.
Failing that, if you have a signal generator, you could try a full
retune on the receiver. On the 034 and 039, this would be L1 to
L6 plus L19.
Failing this, I would start to check whether the radio has had parts
changed or removed. Look for missinng parts or signs of soldering
by a third-party. Check values against the circuit diagram.
If you have a multimeter, you could check voltages through the receiver
against a voltage chart. If the signal levels appear high, or the distortion
is on strong signals, maybe check the AGC voltage.
I should have a voltage chart for the 034 or 039 board, and a full
service manual.
Peter.
barett
"Peter" <pe...@peter.invalid> wrote in message
Peter. The board I have, I think is a PA 039 AA.
L19. The way L19 alters the RX audio is exactly what L4 does to the RX
audio. I don't understand what is wrong to cause L4 to act like this. Or is
this normal for L4 to do that?
Someone has been in the radio before. Messed it up and sold it to me as
working 100%. It would cost me a small fortune to send it back. But I'm sure
it can be put right. Its just knowing what coils are doing what.
He said after I got back in contact that he's sorry for selling it like he
did but needed the money urgent. Now I'm stuck with it.
He said as far as he can remember he turned, L1,L2, L3, L4, L5, L6, L19 and
L14.
I don't have a signal generator. Is there another way?
Peter
>
> Peter. The board I have, I think is a PA 039 AA.
>
> L19. The way L19 alters the RX audio is exactly what L4 does to the RX
> audio. I don't understand what is wrong to cause L4 to act like this. Or is
> this normal for L4 to do that?
>
> Someone has been in the radio before. Messed it up and sold it to me as
> working 100%. It would cost me a small fortune to send it back. But I'm
> sure it can be put right. Its just knowing what coils are doing what.
>
> He said after I got back in contact that he's sorry for selling it like he
> did but needed the money urgent. Now I'm stuck with it.
>
> He said as far as he can remember he turned, L1,L2, L3, L4, L5, L6,
> L19 and L14.
>
> I don't have a signal generator. Is there another way?
Before going on, a disclaimer:
The correct way to do this is to carry out a complete tune with the correct
equipment, procedure and understanding of electronics. What follows will
include "cheap and dirty" tricks.
Incorrect tuning can cause the radio to interfere with other equipment. Mains
equipment has high voltage areas, which can be lethal.
I trust that you understand the risks and will take the necessary precautions.
You accept full responsibility for anything that happens as a result of going
inside the radio.
If in any doubt, you should find someone qualified to do the work.
The purpose of the signal generator is to give the radio a steady, continuous,
low level signal. with clear audio The signal needs to be low and, as you
tune, should be reduced as the gain of the receiver increases. This is
used with a SINAD meter and tune for best S/N reading.
With CB, you can often get away with using a home-made signal generator,
the signal meter and your ears. As long as the meter is reasonably good.
It is possible to make a signal generator from an old CB. Even some
old crabby AM CB can be converted for use as an FM generator. It
has been done and works well for simple tuning jobs.
Next option would be looking for someone local with the equipment. They
may tune the radio for you or even let you use the equipment yourself.
I would not really recommend it but, if there really is no other option, you
could get someone who is at a reasonable distance to key up on channel
20. They should have a low level of continual audio so that you can check
for distortion. They should *not* give you a very strong signal, as this
would increase the AGC level in your receiver. It may help if they have
a low power setting.
L1,L2, L3, L4, L5, L6 and L19 are the receiver tuning. You work your
way from L1 through to L6 and then L19. You want best gain with least
noise or distortion.
L1 and L2 are in the front end, so should be tuned for best signal throughout
the channels. If really stuck, tune these on channel 20 and check for equal
reception on top and bottom channels.
This is where the sig gen comes in. If you are using an incoming signal,
they may be putting out more at one end of the band or your antenna may
work better at one end. A signal generator gives the same input across the
band.
L3 to L6 are in the first and second IF. They are each tuned to a single
frequency, so you can leave it on channel 20. L19 is the quad coil, also
independent of channel.
Adjust VR1 with a maximum signal input (like someone outside your door)
for a reading just at the end of the scale (not pinning on the end stop).
L14 is in the transmit section. You really will need a power meter and
a dummy load to tune the transmitter. You can make a dummy load. It
is just a 50 Ohm, non-reactive resistor.
L14 is adjusted for best and equal power at the top and bottom channels. There
will be an increase in the middle - this is normal. Adjust VR3 for a TX meter
reading in the blank area between the red and green.
There are other adjustments which really need the correct test equipment. If
you need diagrams, component layouts or other details, let me know.
Regards,
Peter.