Connex CX-3300HP low VCO

[Hawkeye351]

Hi all,
Got a Connex CX-3300HP on the desk.

Issues:
Low transmit
Receive delay/fade in

Replaced 1 MOSFET, transmit works great now.

Receive has a delay after unkeying. The receive takes about 1.5 seconds to fade back in. Nearby strong stations sound tight/distorted. VCO buffers aligned great, but Voltage on TP2 will not go any higher than 2.25v before everything drops out. I need that voltage to be 3.20v at TP2.
PLL oscillators lined up great,
Carrier oscillators lined up great,
Buffers lined up great,
RF stage lined up great
Just the VCO voltage on TP2 will not go higher than 2.25v, I need it 3.20v.

Any ideas?

 

[Hawkeye351]

Forgot to mention,
The 10.240mhz crystal is showing as 10.2398mhz. Not off by much at all.

Could C90 cause this?

 

[nomadradio]

TP2 will not go higher than 2.25v,

What's the power supply voltage on the PLL chip? This is one fault that can affect tuning voltage.

73

 

[Hawkeye351]

Voltages checked in receive only, channel 20, ANL/NB off. Radio DC supply is 13.8v.

PLL - Ranger RCI-145106P

1 - 8.43
2 - 4.14
3 - 4.13
4 - 4.16
5 - 4.01
6 - 8.38
7 - 5.44
8 - 3.51
9 - 0.00

10 - 8.62
11 - 8.62
12 - 8.62
13 - 8.62
14 - 8.62
15 - 0.00
16 - 8.67
17 - 8.62
18 - 0.00

Pins 4, 5, and 6 according to the galaxy dx 33hp IC voltage info should have no connection. Pin 7 is high and pin 8 is low.

Would the radio still transmit great on frequency if the PLL was bad?

This radio has all WINCAP brand caps.

 

[nomadradio]

Umm, low signal-input voltage on pin 2 can make this chip get twitchy. Anything above 1/2 or one Volt peak-to-peak AC tends to keep it stable enough. Less that than could cause trouble.

73

 

[Hawkeye351]

Does the voltage for the VCO IF can come from the PLL? Specifically pin 7?

Reason for asking is, when looking over the schematic of the galaxy 33hp, I noticed pin 7 of the PLL feeds TP2 (R116), then it goes toward the VCO, along with 2 tantalum caps in between.

If the VCO gets it's voltage from pin 7 of the PLL through that r116 resistor, then why is it pin 7 directly shows 5.44v (plenty for the VCO) but the test side of that r116 resistor shows less than 2 volts (which it seems feeds the VCO).

Only thing after pin 7, is that r116 resistor. On the pin 7 side of that resistor I get 5.44v but on the other side of that r116 resistor I get less than 2v, and won't adjust any higher using the VCO adjustment. Would those 2 tantalum caps, or anything else between r116 (TP2) to the VCO adjustment make the voltage drop on that r116 resistor, preventing voltage from getting to the VCO adjustment?

I also noticed C90 is tying pin 1 and pin 18 of the PLL together, I have no issue there so that one must be fine, but I did notice C95 is in line with the VCO adjustment.

None of the IF cans top out flush. All the IF cans in this radio peak out around halfway or 3/4 down. Thanks nomad for teaching me about those cans a few months ago.

Everything works great on this radio, except the receive fades back in after unkeying radio, takes about 1.5 seconds for receive to fade back in. Changing channels doesn't do that though, only after unkeying does it do that. And I'm thinking it's because I can't get the VCO to adjust no higher than 2v, when it should be 3.2v. Where the radio works best at is at 1.62v on the VCO adjustment, half of what it supposed to be. At 2v I lose everything, but at 1.62v everything works fine, just low receive and distorted receive on locals. The meter does work great on transmit, but barely moves, even on strong stations (distorted/tight sounding).

Strange that everything drops out when you increase the voltage from VCO adjustment from 1.62v to 2v, when it supposed to be 3.2v. If everything drops out at 2v, then obviously it will still drop out at the 3.2v which is needed. Why would it work best at 1.62v, instead of the required 3.2v (if I could get it that high)?

Guess I'll check those 2 tantalum caps, C95, tr25, c32 and c42.

Issue still remains:
Strong nearby stations distorted/tight sounding.
Receive fades back in after unkeying, around a 1.5 second delay before receive fades back in.
Meter barely moves on receive.

 

[Hawkeye351]

While checking/replacing those few caps, I noticed R116 isn't a 5.6k ohm as the schematic calls for. It's actually a 27k ohm. It's colors are Red/violet/orange.

After replacing those few caps, there was no difference, the issue remains.