DaKandEKid
New Member
I had a printed circuit board made for a radio design based on the phillips TDA7088T. It's almost identical to schematic in the phillips datasheet with the exception i used a bb809 rather then a bb910. And am using 68nH surface mount inductors rather then a 70nH and a 78nH. I was hoping this wouldn't completely ruin the circuit.
For anyone who has built this circuit i've been monitoring the voltage on pin 16 which is supposed to vary from 0 to 1.8 volts when being tuned. Each time you press the 'UP' button:
1) a capacitor will begin to charge which ->
2) effects the capictance of the variacap ->
3) which changes the frequency .....
The voltage on this pin stays at 0V always...
I was wondering if anyone had any input on
Differences between bb910 & bb808
* Cd @ VR = 4.7pF (bb808) vs. 2.5pF (bb909)
* Tuning Range
- Ratio = 9 vs. 16
- V1 = 1 vs. 0.5
- V2 = 28 (same for both)
* Rs Max = .6 vs.1
* Matched Sets = 3 vs. 2.5
Which are the critical values that must be matched in varicaps?
Anyone that is familiar with this circuit how tolerant is the Search Tuning to slight variations (ie 68nH inductor rather then a 78nH & varicap differences).
I'm trying to figure out if I have a problem with the chip or another part or if i just need different components.
For anyone who has built this circuit i've been monitoring the voltage on pin 16 which is supposed to vary from 0 to 1.8 volts when being tuned. Each time you press the 'UP' button:
1) a capacitor will begin to charge which ->
2) effects the capictance of the variacap ->
3) which changes the frequency .....
The voltage on this pin stays at 0V always...
I was wondering if anyone had any input on
Differences between bb910 & bb808
* Cd @ VR = 4.7pF (bb808) vs. 2.5pF (bb909)
* Tuning Range
- Ratio = 9 vs. 16
- V1 = 1 vs. 0.5
- V2 = 28 (same for both)
* Rs Max = .6 vs.1
* Matched Sets = 3 vs. 2.5
Which are the critical values that must be matched in varicaps?
Anyone that is familiar with this circuit how tolerant is the Search Tuning to slight variations (ie 68nH inductor rather then a 78nH & varicap differences).
I'm trying to figure out if I have a problem with the chip or another part or if i just need different components.