Misc Zenith Turn Ons
by G-Man of Group 42
9-176-01 Big Board and Others
Since there are many, many different versions of these decoders,
try looking at all mods and decide which one looks closest to your
unit
On three port (3 jacks on back) model with the 40 pin LSI chip on the back
board, connecting pins 10 and 11 together will enable the video for testing.
On some units, there is a resistor hidden between the chip and the board
which first must be removed.
Audio Turn Ons
In some instances, just connecting pins 3 and 4 together on IC6302
will enable the audio.
Decoder Boards 9-192-02 and 9-192-03
Models STC-1020, STC-1060 and STC-1082
- Short pins 10 to 11 on IC 6675 (Logic Chip)
- Remove resistor R6687 (6.2K on bottom right of board)
- Most units have a diode at location R6678 instead of a 680 ohm
resistor. If there is a resistor at this location, remove it
and install a diode (cathode twards transistor on left.)
- Remove diodes CR6626, CR6627, and CR6628.
- Install a 1K resistor from cathode of diode in step 3 to Jumper W30.
- Remove PROM.
- Power on unit. Adjust Zero Carrier, limiter and horiz osc.
- May have to wait 15 min for video to stabilize.
Decoder Board 9-192-04
Models STC-1000, STC-1085, STC-4010
- Cut jumper W15.
- Connect jumpers W23 and W24 together.
- Connect a wire from jumper W25 (ground) to the collector lead of
transistor Q6675 or to jumper W6.
- Unplug PROM or cut jumper W3.
- Disconnect battery or cut jumper W11.
- On connector J10 short the two pins closest to connector J11.
- Power unit up, adjust zero carrier, agc and horiz osc. If video
is inverted, look at jumper block SM1. If jumper 2 in this block is
installed, remove it. If jumper 2 is not installed, install one.
Video still inverted do the same with jumper 6 of this block.
In jumper block SM1, J4 can be used to forcibly pass video and sound (this
jumper block is a row of 7 jumpers found just to the right fo the 40 pin IC.
SM1 is the name printed on the circuit board for these jumpers. Each jumper
is labled J1 through J7.)
Connecting J3 to J4 will pas bideo and sound if the unit is shut down. This
will not descramble a scrambled picture however. It is only used to thest
the 40 pin logic chip.
