point are working properly. If the picture on
the TV is bad, you are injecting before the
problem. Continue isolating the defective
stages by moving your injection closer to the
output until the injection produces a good
picture.
The “Lum & Chroma” PLAYBACK SIGNAL is
used to troubleshoot defects in the chroma
stages. It provides both the luminance and
down-converted chroma signals for each VCR
format. The VC93 must be phase locked to
the VCR while injecting into the chroma cir-
cuits. Further details on this signal and on
troubleshootingcolorproblemsmaybefound
in Tech Tip #195, “Troubleshooting VCR
Chroma Circuits With The VC93 All Format
VCR Analyzer.”
Injecting the DRIVE SIGNAL
S
Use the DRIVE SIGNALS to inject into the
luminance stages after the FM detector. The
“Lum” Drive Signal is used between the FM
detector output the luminance input of the Y/
C mixer. Use the “Composite Video” Drive
Signal after Y/C mixer output.
To inject the DRIVE SIGNALS:
1. Inset-t a work tape into the VCR and
press play.
2. Set the VC93 as follows:
a. MODULATION to “Color Bars” or
“External”.
b. DRIVE SIGNAL to “Lum” or “Com-
posite Video”.
C
.
D
RIV
E
L
E
V
EL
to "0".
d. Set OUTPUT SIGNAL MONITOR/DVM
to “Drive Signal”.
3. Connect the DIRECT TEST LEAD to the
VC93 DRIVE OUTPUT jack.
4. Connect the DIRECT TEST LEAD to the
VCR:
a. Red lead to circuit test point.
b. Black lead to circuit ground.
5. Observe the picture on the playback
monitor.
6. Adjust the DRIVE LEVEL control for the
best picture.
This injection checks the ability of the video
circuits to process the signal and pass it on to
the video output jack or the RF modulator. If
the picture on the TV monitor is good, all the
circuits between the injection point and the
video output are good. If the picture on the TV
is bad, you are injecting before the problem.
Continue to isolate the defective stages by
moving your injection closer to the output
until the injection produces a good picture.
You are now injecting before the defective
stage.
Fig. 3: Use both red clip leads on the HEAD SUBSTITUTION TEST LEAD to inject in to the
head channels simultaneously (A). You only need to connect one of the red clip leads
when injecting after the A/B headswitcher (B).
