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cobra 148 unlock PLL
- Thread starter Robalo
- Start date
The "148" is the Hot water manifold for the Radiator - and the flange is where the Thermostat sits - the pipe to the left in the photo is for recirculation - heater core circulation bypass so the engine doesn't develop "Hot spots" due to lack of water movement.
Gosh, I hope your vehicles' ok...
To see a rebuilt motor - ... well, it's not because you won the lottery...
Gosh, I hope your vehicles' ok...
To see a rebuilt motor - ... well, it's not because you won the lottery...
No, just never really appreciating the concept of dragging ones butt into the shop and make them pay for the pizza when their insurance won't....
Got reamed a few times for being the guy that had to file "internal damage caused by Accident" claims and not getting proper attention...
You gotta have something to get you to work, they know that and will take advantage at every opportunity - both Insurance and the Shop - you're the one in the middle.
If I could ever get all those vehicles I've owned thru the years back - I'd still have my '75 Nova with the 262 V8 and the 2GC carburetor working better than the stuff they call performance these days...
Along with that my 1991 Tracker, My 87 Chevy Sprint and even the AMC Pacer (Slant 6-straight with it's own Carter 2BBL carb and all those Prestolite issues too...
I wasn't a power hungry beast, more of a practical person whom loved to drive stick.
Got reamed a few times for being the guy that had to file "internal damage caused by Accident" claims and not getting proper attention...
You gotta have something to get you to work, they know that and will take advantage at every opportunity - both Insurance and the Shop - you're the one in the middle.
If I could ever get all those vehicles I've owned thru the years back - I'd still have my '75 Nova with the 262 V8 and the 2GC carburetor working better than the stuff they call performance these days...
Along with that my 1991 Tracker, My 87 Chevy Sprint and even the AMC Pacer (Slant 6-straight with it's own Carter 2BBL carb and all those Prestolite issues too...
I wasn't a power hungry beast, more of a practical person whom loved to drive stick.
ic 4 pin 5 is 13.8v pin 6 8.33v press ptt tr35 goes ground beep but pin 8 does not tx and 6 still has 8.33v is d31 removed pin 8 tx wtf 
i am staring loosing my patience
i am staring loosing my patience
So, in your vid, the TX turns RED...
Saw SWR meter move the needle and showed power...
Your parts laying on that pad, BEFORE or AFTER? (I'm thinking after but...)
WOW only thing I could think of that could be the fault is that green Chiclet (Polystyrene?) cap - put that back in...
C501 on Ricks is listed as 473, but I've got 472 - 10X smaller value.
That is a frequency dependent....part...Pin 9 filter but still, may want to swap that part back in...
Saw SWR meter move the needle and showed power...
Your parts laying on that pad, BEFORE or AFTER? (I'm thinking after but...)
WOW only thing I could think of that could be the fault is that green Chiclet (Polystyrene?) cap - put that back in...
C501 on Ricks is listed as 473, but I've got 472 - 10X smaller value.
That is a frequency dependent....part...Pin 9 filter but still, may want to swap that part back in...
Handy andy Igoing to do this
Lets look further back, into the PLL itself - ok look at pins 1 and 2 as a set, and Pins 3 and 4 as a SEPARATE set. Also Pin 5 and where it is in a loop caught up in those pins. There is also a Pin 6 with a Diode designed to FORCE or Pull power from a line. Follow that line it's goes to a lot of places including the MB3756 Regulator...But come back because we have to see why this, nearly entire half of the chip, isn't oscillating too. Because R163 is a 22K - its'; for the use of Pull-up to keep marginal locks working unless there is a catastrophic failure of the system. Marginal locks? Yes, thermal is one, voltage dropouts from Rx/Tx switching issues - are another, otherwise a slow cap that takes too long to charge onto something pulling down Regulated voltages the PLL looks to - and causing it's own on-board regulator to shift drivers - yes a PLL needs an on-board regulator too so you know...
Notice where and how TP9 works and where it is, it's using the PLL free-running loop pins 1-2 and 3-4
These two pairs form a free running "gated" oscillator - one high speed, another low speed. Between the two - is where Pin 17 is "compared" and if it misses - it sets a count - and too many misses generate a output on Pin 5 - Pin 5 is your correction to the Varactors' ability to make L21, L19 and L21 work...
You mentioned L17 - I think you meant L21 or even L20 - L17 is where? on your board? (it's a coil so it would show a short) Maybe you can scope that one side at a time - and you'd have MHz (Read a LOT OF HERTZ) of frequency on one side but not so many MHz on the other (attenuated) - it's a low-frequency choke - like power supplies use...take a higher frequency ripple and smooth's it out - its is not perfect nor is it used in that fashion - just acts as a high impedance doorway - to keep high-frequency out (stays with the VCO side) and let low-frequency (the Clock Errors - your BEAT Frequency differences) pass into Pin 17 to cycle with the other half f the chip.
Now, if you are getting 33 MHz then it looks like you now have the UHIC chip running, you're just not getting the PLL gating event to compare to Pin 17 - so scope the 1-2 pin and 3-4 pin with a high-impedance probe looking for about 10MHz for starters to see if you can see "clocking" going on.
Why the 1-2 and 3-4 pins? Well, Pin 5 is needed so that the PLL thinks it's ok to compare Pin 17's frequency input and send any data out - thru Pin 5 - so it looks and uses 1-2 and 3-4 mess that cycles - to generate either a pulse or hold low - to correct the Varactor. So if 1-2 and 3-4 are not "oscillating" - Pin 5 won't work and so the PLL thinks something's wrong and sets Pin 6 to lock out everybody from using the signal present.
#37Handy Andy, Yesterday at 3:28 PM
Last edited: Today at 1:21 PM
Lets look further back, into the PLL itself - ok look at pins 1 and 2 as a set, and Pins 3 and 4 as a SEPARATE set. Also Pin 5 and where it is in a loop caught up in those pins. There is also a Pin 6 with a Diode designed to FORCE or Pull power from a line. Follow that line it's goes to a lot of places including the MB3756 Regulator...But come back because we have to see why this, nearly entire half of the chip, isn't oscillating too. Because R163 is a 22K - its'; for the use of Pull-up to keep marginal locks working unless there is a catastrophic failure of the system. Marginal locks? Yes, thermal is one, voltage dropouts from Rx/Tx switching issues - are another, otherwise a slow cap that takes too long to charge onto something pulling down Regulated voltages the PLL looks to - and causing it's own on-board regulator to shift drivers - yes a PLL needs an on-board regulator too so you know...
Notice where and how TP9 works and where it is, it's using the PLL free-running loop pins 1-2 and 3-4
These two pairs form a free running "gated" oscillator - one high speed, another low speed. Between the two - is where Pin 17 is "compared" and if it misses - it sets a count - and too many misses generate a output on Pin 5 - Pin 5 is your correction to the Varactors' ability to make L21, L19 and L21 work...
You mentioned L17 - I think you meant L21 or even L20 - L17 is where? on your board? (it's a coil so it would show a short) Maybe you can scope that one side at a time - and you'd have MHz (Read a LOT OF HERTZ) of frequency on one side but not so many MHz on the other (attenuated) - it's a low-frequency choke - like power supplies use...take a higher frequency ripple and smooth's it out - its is not perfect nor is it used in that fashion - just acts as a high impedance doorway - to keep high-frequency out (stays with the VCO side) and let low-frequency (the Clock Errors - your BEAT Frequency differences) pass into Pin 17 to cycle with the other half f the chip.
Now, if you are getting 33 MHz then it looks like you now have the UHIC chip running, you're just not getting the PLL gating event to compare to Pin 17 - so scope the 1-2 pin and 3-4 pin with a high-impedance probe looking for about 10MHz for starters to see if you can see "clocking" going on.
Why the 1-2 and 3-4 pins? Well, Pin 5 is needed so that the PLL thinks it's ok to compare Pin 17's frequency input and send any data out - thru Pin 5 - so it looks and uses 1-2 and 3-4 mess that cycles - to generate either a pulse or hold low - to correct the Varactor. So if 1-2 and 3-4 are not "oscillating" - Pin 5 won't work and so the PLL thinks something's wrong and sets Pin 6 to lock out everybody from using the signal present.
- What can throw you for a loop here (SIC) is the fact that the TP9 has both DC and a weak AC component to it on the same line at the same time. If C90 (R104 / C90) is bad or shorted, you'll have too low of power to even get the oscillator to start. so look for and check values on that TP9 line...
#37Handy Andy, Yesterday at 3:28 PM
Last edited: Today at 1:21 PM