mal1958au
Member
Hi,
As a bit of background about an Icom R7000 with a PLL fault that I am trying to fix.
I recently bought a R7000 to do up to sell. It was being sold as faulty and based on the description of the fault, it sounded a lot like the typical caps on the DC/DC converter and on the display.
When I got the radio, not only was the display intermittent there were random characters, and total silence from the speaker.
A check the voltages on the DC/DC converter confirmed that the capacitors needed replacing along with the ones on the display board.
With the the new capacitors, the display came up nice and clear except that were occasionally random characters like "o" and "I". A check on the logic board suggested that a couple of capacitors around the 5V power supply where a bit dry and need to be replaced. This was duly done and this has improved but is still not 100%, but can be fixed by turning the radio on/off a few times. I suspect that the electrolytic capacitor on the CPU Reset line needs to be replaced.
I find now that the display responds to the tuning knob, the different modes etc. Except, lots of key bounce when inputting the frequency via the front panel. I hope that this is just because the switches behind the keys need a clean. (The radio is particularly dirty).
Strangely the radio is still silent except for some slight hiss on the speaker.
Now the Issue with the PLL. This is where I need some clues.
It turns out that the receiver is muted by the PLL. Muting by the PLL occurs if a blank memory channel is selected, or if in fact the PLL has a fault and is unlocked.
I have confirmed that the PLL control chip (IC3 -M54929P) is indicating an out of lock condition.
The VCO control voltage Signal (PD) is at the maximum range (15V) and the signal presented to the prescaler (IC4 - M54466L) is mostly "noise".
I can simulate a more reasonable control voltage (5V) signal by disconnecting the 24V feed from the RF unit, but the "noise" signal presented to the prescaler really doesn't change.
I have checked most DC voltages marked on the cct diagram throughout the PLL board and they are all within a small margin of the voltages marked on the circuit diagram.
I don't have the test gear to do the RF levels, but have a 100Mhz CRO that can see some waveforms.
I think the VCO block is working OK, I think that the Prescaler and Controller are working OK. I am not sure about the output from IC5 (Buffered VCO Output) and the IC8 mixer.
Has anybody had experience trouble shooting the PLL in a R7000 ?
I am quite at a loss on this one.
Any clues or suggestions would be welcome.
Cheers,
Mal (from Oz)
VK3AZZ
As a bit of background about an Icom R7000 with a PLL fault that I am trying to fix.
I recently bought a R7000 to do up to sell. It was being sold as faulty and based on the description of the fault, it sounded a lot like the typical caps on the DC/DC converter and on the display.
When I got the radio, not only was the display intermittent there were random characters, and total silence from the speaker.
A check the voltages on the DC/DC converter confirmed that the capacitors needed replacing along with the ones on the display board.
With the the new capacitors, the display came up nice and clear except that were occasionally random characters like "o" and "I". A check on the logic board suggested that a couple of capacitors around the 5V power supply where a bit dry and need to be replaced. This was duly done and this has improved but is still not 100%, but can be fixed by turning the radio on/off a few times. I suspect that the electrolytic capacitor on the CPU Reset line needs to be replaced.
I find now that the display responds to the tuning knob, the different modes etc. Except, lots of key bounce when inputting the frequency via the front panel. I hope that this is just because the switches behind the keys need a clean. (The radio is particularly dirty).
Strangely the radio is still silent except for some slight hiss on the speaker.
Now the Issue with the PLL. This is where I need some clues.
It turns out that the receiver is muted by the PLL. Muting by the PLL occurs if a blank memory channel is selected, or if in fact the PLL has a fault and is unlocked.
I have confirmed that the PLL control chip (IC3 -M54929P) is indicating an out of lock condition.
The VCO control voltage Signal (PD) is at the maximum range (15V) and the signal presented to the prescaler (IC4 - M54466L) is mostly "noise".
I can simulate a more reasonable control voltage (5V) signal by disconnecting the 24V feed from the RF unit, but the "noise" signal presented to the prescaler really doesn't change.
I have checked most DC voltages marked on the cct diagram throughout the PLL board and they are all within a small margin of the voltages marked on the circuit diagram.
I don't have the test gear to do the RF levels, but have a 100Mhz CRO that can see some waveforms.
I think the VCO block is working OK, I think that the Prescaler and Controller are working OK. I am not sure about the output from IC5 (Buffered VCO Output) and the IC8 mixer.
Has anybody had experience trouble shooting the PLL in a R7000 ?
I am quite at a loss on this one.
Any clues or suggestions would be welcome.
Cheers,
Mal (from Oz)
VK3AZZ
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