this galaxy 33 will not adjust to the right frequency the volts are off at tp2 ive changed the caps ,pll, and checked the diodes . and checked all 3 crystals. to get it on channel 1 the volts will be 8.65 volts at tp2 but the channnel selector will show another channel but it is still on the frequency set at channel one
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galaxy dx 33 hp2 problems
- Thread starter curtis charles
- Start date
PLL problems fall into two basic categories.
First, there is a missing input to the PLL that it needs to function.
If the 10.24 MHz feeding into pin 3 of the MC145106 PLL chip is weak or missing, that causes this sort of symptom.
Likewise if the downmixed VCO frequency feeding into pin 2 is weak or missing, that will prevent the circuit from locking in to the correct frequency.
The binary inputs on pins 9 through 17 have to be right. The two CD4008 chips that feed into those pins will fail from time to time. I have no idea what causes this.
The other common fault is for the PLL to have all the proper inputs, but for the VCO to fail, and not track the tuning voltage coming from the PLL. That model has been in production for over 25 years, so the components in that circuit have been revised more than once along the way. In the late 1990s we saw a lot of bad 10.24 MHz crystals. Hasn't been so common a problem the last 20 years or so. And radios built in the last 20 years will have a surface-mount varactor diode controlling the VCO circuit. It's on the pc board's solder side, and will fail for no obvious reason. Never saw this problem when they used a varactor diode with wire leads on it.
In almost 50 years of dealing with PLL circuits I have never learned to troubleshoot one without an oscilloscope. Always had one on hand when needed.
Somebody smarter than me maybe knows how to do this with only a meter, but I don't.
73
First, there is a missing input to the PLL that it needs to function.
If the 10.24 MHz feeding into pin 3 of the MC145106 PLL chip is weak or missing, that causes this sort of symptom.
Likewise if the downmixed VCO frequency feeding into pin 2 is weak or missing, that will prevent the circuit from locking in to the correct frequency.
The binary inputs on pins 9 through 17 have to be right. The two CD4008 chips that feed into those pins will fail from time to time. I have no idea what causes this.
The other common fault is for the PLL to have all the proper inputs, but for the VCO to fail, and not track the tuning voltage coming from the PLL. That model has been in production for over 25 years, so the components in that circuit have been revised more than once along the way. In the late 1990s we saw a lot of bad 10.24 MHz crystals. Hasn't been so common a problem the last 20 years or so. And radios built in the last 20 years will have a surface-mount varactor diode controlling the VCO circuit. It's on the pc board's solder side, and will fail for no obvious reason. Never saw this problem when they used a varactor diode with wire leads on it.
In almost 50 years of dealing with PLL circuits I have never learned to troubleshoot one without an oscilloscope. Always had one on hand when needed.
Somebody smarter than me maybe knows how to do this with only a meter, but I don't.
73
ive tried everything changed 4008 ICs all transistors, pll chip, checked diodes for the binary and all caps.
Pin 9 is being fed from one of the two 4008 chips. If that voltage is wrong, this is where it comes from.
Question is why?
I'm used to watching the VCO tuning voltage on the 'scope while changing bands. You might want to see if the voltage at pin 9 changes when the band switch is changed. If it's high on all the bands, that would suggest a soldering problem of some sort, if the 4008 chips are brand new. And if you salvaged them from another radio, maybe they're good. Maybe not.
73
Question is why?
I'm used to watching the VCO tuning voltage on the 'scope while changing bands. You might want to see if the voltage at pin 9 changes when the band switch is changed. If it's high on all the bands, that would suggest a soldering problem of some sort, if the 4008 chips are brand new. And if you salvaged them from another radio, maybe they're good. Maybe not.
73