I have a Motorola R2001A service monitor that is having a synthesizer problem. It generates a signal and the spectrum analyzer works but everything is on the wrong frequency. It seems to move in even numbered increments bit not is odd numbers? I have a schematic of the RF systhesizer but have no idea where to start looking. Anyone in the brain trust have a hint?
Thanks,
Jack
K6YC
Help with R2001A repairs
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Re: Help with R2001A repairs
Hi Jack,dechief wrote:I have a Motorola R2001A service monitor that is having a synthesizer problem. It generates a signal and the spectrum analyzer works but everything is on the wrong frequency. It seems to move in even numbered increments bit not is odd numbers? I have a schematic of the RF synthesizer but have no idea where to start looking. Anyone in the brain trust have a hint?
Thanks,
Jack
K6YC
How far off frequency is your analyzer? Does the freq error increase as you increase from low band to high band to UHF to 800? Are there places where you lose the synthesizer lock completely and then get it back at other frequencies? Is the error dependent upon one specific digit of the frequency (such as 100 KHz digit or 10 KHz digit)?
Dave
Re: Help with R2001A repairs
I just checked it and it is not linear, using various hand held radios here are some of the results: If I transmit on 927.2 MHz the Spectrum analyzer says it is on 925.3 MHz a -1.9 MHz error. If I transmit on 445.0 Mhz the analyzer shows 448.2 MHz or a -3.2 MHz error. When I input 145.0 MHz the analyzer shows 125.5 MHz which is -19.5 MHz. and if I input 50.0 MHz the analyzer shows 30.5 Mhz which is also -19.5 MHz. The synthesizer appears to be locked at all times on the frequencies I tested.
On the generate side, when I set the R2001A to 900.0 MHz it generates a signal on 880.5 MHZ. When I set it to 700 MHz it generates a signal on 719.5 MHz. When set to 500 MHz it generates a signal on 519.5 MHz. Set to 300 MHz it generates a signal at 309.7 MHz. Set to 100 MHz the output is 119.6 MHz. It looks like a pattern with a + or - 19.5 error?
The 10 MHz oscillator is right on according to my GPS locked standard oscillator, and the service monitor acts the same with external reference as it does on the internal oscillator.
One thing I did notice was the frequency does not change when entering some numbers. When I set the R2001a to 100.0000 MHz the frequency does not change when I set it to 100.1000 but it does increment at 100.200 but stays the same at 100.3000? None of the numbers below 0.X does anything but it does change on the display on the screen. When incrementing up, .0 and .1 are the same, .2 and .3 are the same, .4 and .5 are the same and none of the less significant numbers change the output frequency.
Now my head hurts!
Jack
K6YC
On the generate side, when I set the R2001A to 900.0 MHz it generates a signal on 880.5 MHZ. When I set it to 700 MHz it generates a signal on 719.5 MHz. When set to 500 MHz it generates a signal on 519.5 MHz. Set to 300 MHz it generates a signal at 309.7 MHz. Set to 100 MHz the output is 119.6 MHz. It looks like a pattern with a + or - 19.5 error?
The 10 MHz oscillator is right on according to my GPS locked standard oscillator, and the service monitor acts the same with external reference as it does on the internal oscillator.
One thing I did notice was the frequency does not change when entering some numbers. When I set the R2001a to 100.0000 MHz the frequency does not change when I set it to 100.1000 but it does increment at 100.200 but stays the same at 100.3000? None of the numbers below 0.X does anything but it does change on the display on the screen. When incrementing up, .0 and .1 are the same, .2 and .3 are the same, .4 and .5 are the same and none of the less significant numbers change the output frequency.
Now my head hurts!
Jack
K6YC
Re: Help with R2001A repairs
Since you don't get an out of lock indication, I don't suspect the synthesizer as your problem. With the analyzer symptoms you describe, I would concentrate on the Processor I/O module (A7). The synthesizer is the fat module in the middle of the card cage. To the right of it is the audio synthesizer and the next one is the processor I/O. There are a couple of PIA chips on this board (I'm mentioning these for easy identification only). Unfortunately, I don't have a service manual but this is where I think your problem is.
Dave