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Cobra 25 Ltd classic
- Thread starter kaos513
- Start date
It wouldn't - but if you want my help - I think if you look at a Cobra 25 using the KEPC PLL chip - you'll see what I mean. The "yellow" circle - That's R150 - someone's been in it, they clipped a resistor out so you want help or do you want to figure this one out on your own?
9106 chips used a 47K buffer...you don't have that in there - and hope it didn't blow it up from excessive VDD that exceeded the 5 V DC regulation - which will kill that PLL chip soon enough - it TX's now, you just don't have the RX...
So did you check for that 455kHz shift yet?
9106 chips used a 47K buffer...you don't have that in there - and hope it didn't blow it up from excessive VDD that exceeded the 5 V DC regulation - which will kill that PLL chip soon enough - it TX's now, you just don't have the RX...
So did you check for that 455kHz shift yet?
Ok, so you know, the 9106 and the 9109 use T/R pins at location Pin 8 - but their "On" states are reversed.
9106 - Pin 8 is High in Transmit
9109 - Pin 8 is Low in Transmit
So your IF is already "shifted" - so you see your Frequency counter - your channel plan is the same, but the LOOP IF is 455kHz off - needs to be lower to match the TX frequency correctly without having to mess with that CF2 variable cap, VC1. To Slide it down to where you need it. It's not it's fault, the PLL needs the "logic" of it (Pin 8 T/R Shift) reversed.
Can be something as simple as Pin 3 TX on the Mic wire, or the RX/TX light to do this. You need a method to revert the PLL from 1 state for it's shift, to a 0 state for it's shift.
9106 - Pin 8 is High in Transmit
9109 - Pin 8 is Low in Transmit
So your IF is already "shifted" - so you see your Frequency counter - your channel plan is the same, but the LOOP IF is 455kHz off - needs to be lower to match the TX frequency correctly without having to mess with that CF2 variable cap, VC1. To Slide it down to where you need it. It's not it's fault, the PLL needs the "logic" of it (Pin 8 T/R Shift) reversed.
Can be something as simple as Pin 3 TX on the Mic wire, or the RX/TX light to do this. You need a method to revert the PLL from 1 state for it's shift, to a 0 state for it's shift.
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Well, don't throw out the Baby with the Bathwater...
It's not that bad, you already know that the BCD encoding for these PLL's are all nearly the same from the 5126 onto the 9106, 9109 as well as 2816, 2814 - the only thing that is different for the SSB radios is they use 5kHz versus the 10kHz spacing.
So really, your 9106 versus 9109 - they simply changed (minor revision excluded) is how the T/R pin shifts and when.
You have a radio that used a KEPC knockoff of the 9109 chip, you are swpping in a 9106 - it's the wrong one for the job, UNLESS you provide for the switching effort...
Follow me? You can use 9106 in there, just the 9109 has a different LOGIC switch value - opposite of what 9106 uses...
Here's an example...
9109 - uses GROUND on Pin 4 on the Mic -(speaker and RX return)
This is what they'd call LOGIC LOW
Pin 4 engaged at the MIC,
Speaker and RX return works to GROUND
So PLL Pin 8 is GROUNDED.
When you switch to PA - CB/PA switch FLOATS PLL Pin 8
so the 455kHz doesn't occur - you have no RX
This is the 9106 switch scheme...
When TX is on, Pin 8 is LIVE
So all you need to figure out is which side of the TX switch you want the chip to work.
When Pin 3 floats, it's HIGH.
Then Pin 3 goes LOW - to GROUND
other places go HIGH in TX
(at the MIC connector)
When you need Pin 8 high, as in TX, remember then too - the 455kHz shift - is dropped.
So that means the RX shift is on Logic LOW of Pin 8.
You'll need a "pull down" (~10K to 22K) resistor to ENSURE the logic level is set LOW when the HIGH - or TX - is not on.
You'll need the BUFFER resistor (4.7K) to keep the TX Logic HIGH from damaging the chip.
With the above in mind, take a moment then to engage Pin 8 now that you have a correctly placed Varicap to help your 10.240 "trim" to meet TX - your RX should return - once you figure out if it needs (5V) High or (GND) Low to make the RX frequency "Line up" the RX strip and you get your receive back.
It's not that bad, you already know that the BCD encoding for these PLL's are all nearly the same from the 5126 onto the 9106, 9109 as well as 2816, 2814 - the only thing that is different for the SSB radios is they use 5kHz versus the 10kHz spacing.
So really, your 9106 versus 9109 - they simply changed (minor revision excluded) is how the T/R pin shifts and when.
You have a radio that used a KEPC knockoff of the 9109 chip, you are swpping in a 9106 - it's the wrong one for the job, UNLESS you provide for the switching effort...
Follow me? You can use 9106 in there, just the 9109 has a different LOGIC switch value - opposite of what 9106 uses...
Here's an example...
9109 - uses GROUND on Pin 4 on the Mic -(speaker and RX return)
This is what they'd call LOGIC LOW
Pin 4 engaged at the MIC,
Speaker and RX return works to GROUND
So PLL Pin 8 is GROUNDED.
When you switch to PA - CB/PA switch FLOATS PLL Pin 8
so the 455kHz doesn't occur - you have no RX
When TX is on, Pin 8 is LIVE
So all you need to figure out is which side of the TX switch you want the chip to work.
When Pin 3 floats, it's HIGH.
Then Pin 3 goes LOW - to GROUND
other places go HIGH in TX
(at the MIC connector)
When you need Pin 8 high, as in TX, remember then too - the 455kHz shift - is dropped.
So that means the RX shift is on Logic LOW of Pin 8.
You'll need a "pull down" (~10K to 22K) resistor to ENSURE the logic level is set LOW when the HIGH - or TX - is not on.
You'll need the BUFFER resistor (4.7K) to keep the TX Logic HIGH from damaging the chip.
With the above in mind, take a moment then to engage Pin 8 now that you have a correctly placed Varicap to help your 10.240 "trim" to meet TX - your RX should return - once you figure out if it needs (5V) High or (GND) Low to make the RX frequency "Line up" the RX strip and you get your receive back.
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Huh?
RIP, er, no, possibly wrong PLL 9106 vs 9109 <<<-Your board is a 417 from UNIDEN...
So what did you do... to try reversing and toggle the T/R pin?
Got a Cobra 25ST schematic? PLL in the 25LTD is similar to the 9109
You can also try a SM5126 PLL - since you have the socket
You will have to retune L15 to make it ring in RX L16 L17 and L18 to peak TX stuff...
Remember your 455kHz shift...now it should be opposite- if you tried to change the T/R pin.
RIP, er, no, possibly wrong PLL 9106 vs 9109 <<<-Your board is a 417 from UNIDEN...
So what did you do... to try reversing and toggle the T/R pin?
Got a Cobra 25ST schematic? PLL in the 25LTD is similar to the 9109
You can also try a SM5126 PLL - since you have the socket
You will have to retune L15 to make it ring in RX L16 L17 and L18 to peak TX stuff...
Remember your 455kHz shift...now it should be opposite- if you tried to change the T/R pin.
You have a Frequency counter - I'm curious to know what channel 19 frequencies are at TP3 when in RX then TX.
Why?
Again, the 455kHz shift, see which way it goes...
Why?
Again, the 455kHz shift, see which way it goes...