Philips CD304 MK II - RF Pre-Amplifier Checks

-10
b. Dynamic
Insert disc, select service loop A and check if the signal on
point > equals to 7 Vpp.
— Select service loop B.
Now RCO = high and RCO = low.
So switch Y, is in position 1.
Switch Y, switches at f = 650 Hz.
Point €> is low; SO point 6} is in phase point 6d.
Now Fig. U should be present on point $> with duty
cycle jittering round 50%.
Annex V: CHECKING RF PRE-AMPLIFIER
(measure points on pre-amp: PCB)
a. Check DC-voltages on transistors 6103, 6104, 6105,
6109, 6110, 6111.
b. For checking sensitivity, frequency and delay charac-
teristic, proceed as follows:
— Take flex PCBs of sockets 10 and 11.
— Take plugs 18, 17, 12, 13, 14 and 15 out of
sockets.
Attention: do not take of plug 16 (= supply!).
— Unscrew PCB to enable injection at the copper side
of the PCB.
Checking sensitivity
— Inject Vi, = 140 MVey, 50 KHz on points 102, 101
via R = 100 kM and C = 39 pF (see Fig. A).
— Vout has to be 245 mV + 2 GB.
Note:
Ensure that injection cord and test cord are identical.
H.E
PRE. AMP
Fig. A
CS 5 228 GB
Checking frequency and delay characteristic
— Adjust V;,, in such a way that Vou = 245 mV = 0 cB at
50 kHz.
— Between the injected and the measured sine-wave
signal the delay should be 450 ns + 50 ns at 300 kHz.
This can be measured on the dua! beams oscilloscope
with V;, on beam A and V,,y, on beam B according to
Figure B.
— Check frequency and delay characteristic for fre-
quencies given below:
—_— ————
Frequency Vout Delay Delay,
(kHz) (dB) (n sec.) compared
with delay
at
300 kHz
+ —50 +20
200 +1 +1 0 +20
300 + 1,5 +1 450 +50 0
500 + 35241 +20 +20
700 + 5542 +30 +20
+8 +30 +20
+8
+4
vil
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iat |
33 393A12 Fig. B 33 394A12