Sony ta n 8550 service manual

Page 2

TAN-8550

SERVICING NOTES

I. Apply the rated ac line voltage to the set directly. Do not increase the voltage gradually by using a variable
transformer or other such instrument: this will cause a V-FET failure.

(a

V-FET Replacement

TAN-8550 uses six V

25118...3 pcs) in each channel of its power ZSKGO R725, R775 R73". R781

amplifier. Both zsxso and 2SJl8 are divided 23" R731 R782

into six ranks according to their ng0 (gate- 53 33 kSl l.8k§l '
source voltage) and Vp (cut-off voltage). The 54 33 kn 1,5k9

bias resistors of the V-FET-differ from a rank

to a rank, and it is'ne'cessary to use the same 55 33 k9 1-2 k9 '
rank of V-FETs in the same channel. 56 30 k9 1.0 kg

If you cannot obtain the same rank of V-FET 57 30 k9 1.0kfl

as the one used in the repairing set, replace all

six V-FETs. At the same time, replace the bias 58 30 id! 820 Q

resistors according to the table given at right.

(2SK60/25J18}
rank (5.? 58)

3.A{ter the replacement of V-FET, carry out the following check to avoid further oecurance of V-FET failure.
1) Turn off the power of TAN-8550.

V It d ss
1) Remove the heat sink duct, Rank of 3:59;? o :3? 2:38.330
3) Disconnect the brown and the violet lead USBd in the 59 R787 (RCH)
wires from the pins on the CLASS B 53 18.8~23.8V
POWER AMP BOARD, See the figure 54 23,8~ 28.8V
at bottom rtght.
' 55 28.8 ~ 33.8 V
4) Turn on the power and check the voltage
across R737 (L-Cl-l)/R787 (R-CH). 1f the 56 3348 ~ 38i8V
reading does not agree with the value 57 38.8 ~43.8V
given in the table at right, try adjusting 58 43lg~43_g V
RT701 (L-CH)/RT751 (RvCH).
5) If adjusting RT70l/Rl75l still does not
give correct reading. check Q713Q7l6
(LrCH)/Q7b3~Q766 (R-CH). Failure of
these transistors Will cause V-FET failure.
VTVM
6) After the check, turn off the power of the I
set and put back the two lead wires
mentioned in step 3, L
0715IL CHI fl % IRRT77'917} E}
i r 0777~o719 IL-CH) R737 J ,., '
0765 (H CH " r; o757~o769 (Atom i (R787) V\ l
«O
" R737 IL-CH) x 0775 53577566, 1 \d
1 m7 (R-CH) W (0765) L
"_ Class B Power Amp
To 0720~0722 (L-CHI y WWW" "de
0716 (L~CHI Tn Q770~O772 liq-CH} J
0766' (Ft-CHI c