Cobra CB Radio MODEL(s): All versions of the 29LTD, including models with weather, Soundtracker, and Nightwatch.
DESCRIPTION: We have switched to a different PLL chip (IC1). The older chip is the "2816", and the new chip now says "29LTD" on it.
ACTION: If IC1 is a 29LTD, then it must be replaced with another 29LTD. Do not try to
use a 2816. If IC1 is a 2816, then you can use the 29LTD provided you install the modifications detailed in the following pages.
ADJUSTMENTS: It is recommended to realign the PLL section after replacing IC1.
NOTES: Parts required:
- 680Q 1/8W resistor, Cobra p/n 002-001
- 100uH choke, Cobra p/n 041-001
- 120pF capacitor, Cobra p/n 020-005
- 180pF capacitor, Cobra p/n 020-006
- Sleeving for the resistor
Replacing a 2816 PLL chip with a 29LTD PLL chip:
1. Add the 180pF ceramic capacitor between pins 21-22 of IC1.
2. Cut the circuit trace between C93 and pin 22 of IC1.
3. Add the 100^H choke between C93 and pin 22 of IC1.
4. Add the 680Q resistor between pin 6 of IC2 and the collector of TR20. Use the sleeving on the resistor to prevent its leads from touching any circuit traces.
5. Change C86 from 330pF to 120pF.
6. Remove R85.
The diagram provide additional details.
September 13, 2001 Cobra TECHNICAL SERVICE