Uniden Washington (8719) question

[Hawkeye351]

Got a beautiful Uniden Washington (8719 PLL) on the desk today.

Issue(s):
USB and LSB doesn't have the same tone on receive or transmit. Trebly sounding.
Expo kit acting up.


Evaluation:
D20 has a 5.6uh choke tied on to the banded end and goes to empty hole where banded end of D20 was lifted.

Trimmer caps on expo was dirty.

Clarifier mod looks complete.
Expo install looks complete.
AM and LSB oscillators will adjust fine to their factory spots, but USB will not go lower than 80 on the last digits (should be 75 or 65).

All limiters intact.
Bias slightly off.

Anyone have any insight into the 5.6uh choke tied off to D20 and what it's purpose is?

 

[Hawkeye351]

Nevermind, I found out it's to increase slide on the unlocked clarifier.

 

[nomadradio]

Putting the choke in series with the varactor diode only works correctly on the radios with three coils, one to trim the PLL for each mode. Cobra 148,2000, President Madison etc. This radio has a trimmer cap for USB and a coil each for AM and LSB. Doesn't seem to treat that choke the same way.

This oscillator circuit is different, and would get squirrelly with the clarifier all the way one way. Our cure was to cut the trace on one side of the 11.1125 crystal and bridge the gap with the choke. The free end of the varactor goes back where the factory had put it. Seems to be more stable.

73

 

[Hawkeye351]

I removed that choke from D20 and put the diode back in it's place. I have the choke laying on my desk. Should I do what you stated above on where to place the choke?

Also, why can't I get the USB trimmer cap for the PLL synthesizer oscillator no lower than 34.9880? Should be 34.9875 right?

Also, USB receive and transmit sound awfully tinny sounding (too trebley, no bass). LSB and AM are fine, even dead on frequency.

Thank you Nomad for popping in.

 

[Hawkeye351]

Fixed!!!

D20 had a 5.6uh choke tied to it.
I removed the choke and placed D20 back to stock.

D35 had a jumper across it. I removed the jumper to go back stock.

D37 had a jumper across it. I removed the jumper to go back stock.

CT1 was the wrong value. Left it in place but tied a 10pf disc cap across its leads.

I left the standard unlock procedure the way it is.
R187 removed
D36 removed
Clarifier wires tied to ground and +8v.

USB aligned perfectly with clarifier dead center.

LSB and AM aligned perfectly with clarifier dead center.

USB and LSB tone now sounds almost identical.

Everything is dead on frequency perfectly now, sounds awesome on all modes in receive and transmit.

 

[nomadradio]

Rock on! Gotta love it when a plan comes together!

73

 

[Hawkeye351]

Just noticed a couple things I'm curious of with this radio.

1. The S-Meter swings backwards on received signals.
2. Transmit has a poot (fart) sound when keying up. All limiters are intact and no power mods applied, but still have a fart sound when keying up.

Everything else on this radio is great.

 

[nomadradio]

You're stuck with the S-meter behavior unless you come up with a mod for the radio's AGC circuit.

The keyup poot is caused by a transistor that's meant to silence the receive audio any time the PLL loses its grip, er "lock" on the channel frequency. Only seems to do this after the AM modulation gets turned up. Go figure. Removing it is the only cure I know.

The schematic shows this transistor as TR45, a 2SA733. Just one problem, there is no screen print legend on the board to identify it. Had a picture of it on ImageShack, but they seem to have lost it.

I'll see if that pic is still on the system at work next time I'm there.

73

 

[Hawkeye351]

Is this the write you are talking about?

Post in thread 'uniden Washington Key Up Noise' https://www.worldwidedx.com/threads/uniden-washington-key-up-noise.247551/post-688996

 

[loosecannon]

Hawkeye,

be sure to check my post in that thread you linked to.

the added bonus of the channel selector not silencing the receive while turning the knob is very useful, and i have a feeling you'll start doing this mod to all the 8719 radios you work on.
LC