Synch Regenerator Information

--(GATED) SYNC REGENERATOR--

The following are the most frequently asked questions about the universal descrambler/synch regenerator. A 20 Mhz scope and frequency counter are a must for trouble shooting.

1. R7 There has been some confusion as to the correct connections around R7 and the polarity switch S3. If one closely examines the PC board, R7 can either return to +5V or to ground. R-E Fig3 and Fig4 (P40,41) seem in conflict. If R7 is returned to ground then +5V is supplied through S3. If R7 is returned to +5V, then ground should be supplied through S3. Actually R7 was intended to either return to ground or +5V to allow various interfacing methods for experiments in automatic polarity switching.

2. Pin 9 IC5 This pin will normally read +0.2 to +0.3 volts; not -0.2 volts as in R-E P43 Column 1. Q2 produces a narrow(2msec) positive going pulse during burst intervals to IC5 pin 9 and therefore a VOM or DVM will read only a very small positive voltage.

3. Pins 5 & 10 IC1 are -5V and +5V respectively.

4. The correct frequency signal at pin 23 IC9 is 503.496 khz (503.5 khz nominal) not 1.08 Mhz as shown in R-E. The output from IC6 (divided by 455) should be 7867.13 hz. If this is not the case, check D1-D6.

5. One must have a 4V to 5V P-P square wave at P23 (503.5 khz) before the decoder will operate.

6. IC9 The voltage at pins 13, 11, and 5 may vary considerably or even read zero, depending on the meter used to measure them. Verify 503 khz clock is present on Pin 23 IC9.

7. IC8 divides by 64, not 128. Pin 12 shown is actually pin 2.

8. IC10 may run somewhat hot. Do not apply more than 15 vac to J3 without providing a heatsink on IC10. This heatsink is not provided with the kit.

9. Ringing on picture - Check IC1 and verify that C2, C3, C4, and C5 are in the circuit and OK. Try a .01 bypass between IC1 pin 14 and ground (connect across R4)

10. -0.45 volts is supplied to IC3 Pin 2, not IC2 Pin 2 as in Column 1 page 43.

11. Locking of picture in some cases can be improved by changing R20 and R21 (1K each) to 470 ohm. However, before doing this check C17, L1, Q1, R22, R23, and C18.

12. Incorrect hue can be shifted to improve color by adding capacitance (try 33 pf) across C32. If this makes things worse, then try changing C30 from 56 pf to 33 pf without the 33 pf across C32.

13. Color stability is a function of accurate lockup. The burst key pulse (IC9 Pin 11) is somewhat narrow. Try resetting lock with S1. If no help, make sure that the video signal is clean. Some experimenters have reported that IC6 can produce "glitches" or momentary intermittent miscounting. A change of value of R36 (try 1K ohm) and also of C36 (try values from 820 pf to .0015 uf) has helped in these cases.

14. Smear may be caused by incorrect frequency response somewhere in the video system. This is generally an interface problem. Try the following:

Remove IC2 and IC3.
Jumper IC2 pin 2 to pin 15 and IC3 pin 3 to pin 15.
Now using a good off the air NTSC signal (not scrambled), connect video into J1 and examine video out of J2. If OK, the problem is not in the descrambler video circuit.
restore normal connections and check IC2 and IC3. If OK, the problem is in the video source. A typical case with a non-scrambled signal, the picture is OK, but with a scrambled signal, there is smear, blotchy color, shadowing,or poor contrast.

Remember that your VCR, TV tuner or video source may not operate properly with a scrambled video signal. The horizontal and/or vertical pulse are missing or distorted. Your equipment may contain circuitry that depends on these pulses for some phase of operation (AGC, DC restoration, etc.) and therefore may further distort a scrambled signal. The reconstituted signal may therefore show these distortions. Therein were no such problems in the prototype circuits, so there shouldn't be any problems inherent in the descrambler. The following points should be considered:

The video source should ideally be right off the video detector of the TV tuner or receiver with no extra amplifiers or other circuitry. Sag, excess tilt, or other waveform distortions can occur due to low frequency response or phase shift in the coupling capacitors.
The fact that "every else works OK without the descrambler in the system" is meaningless due to the aforementioned considerations.

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