Sony ta 4650 service manual

Page 2

hi - ii
Service Bulletin No.62

90m CORPORATION or AMERICA Medan $342225 452226 8650
Technical mbh'carions Department _ _

0747 v." Dun smut, Lou Island City. Now York 11101

Subwct V-FET Replacement

Date: August 15, 1977

Refer also to Hi-Fi Service Bulletins No. 41, 49, and 51.

Perform the following procedure if V-FET failure is suspected.
To avoid damage to a replacement V-FET, do not replace without
first making this check.

1, Turn off the power and remove the suspect V-FET.

2. Check resistance readings of this V-FET using a VOM set to the

X19 range. See illustration below.
0 VOM set to X19 range.
<3 S to D _______ Approx. 1~20
S to G _______ Same as a diode
D G S D to G _______ Same as a diode

23.118. ZSKGO

If readings appear normal, the V-FET is probably okay, and
other circuit components should be Checked.

3. If readings are not normal, turn on the power with the V-FET
still out of the circuit. Set the VOM to the 50 VDC range
(or as close as possible) and connect the leads to the ViFET
conductor patterns on the board as follows:

V-FET Source gate
28.118 VOM (+) VOM (-)
ZSKGO VOM (-) VOM (+)

4. Set the dc bias adjust resistor (see below) on the Power Amp
Board for maximum reading.

TA-4650, -5650 - RTvSOl (RT-351)
TA-8650, TAN-8550 - ET-70l (RT-751)
TAN-5550 - RT-501 (RT7601)

5. Turn off the power and install the replacement V-FET. Reapply
power and reset the dc bias according to the service manual for
the respective model.