Phobosx
Phringe
I have an old Toshiba SA-775 here I was hoping to fix. The unit would not come out of protection, but no fuses were blown. Initially, I found that Q 601 & Q603 were shorted. I remove them and then the system played through the good channel.
I ordered some MJE21194 & MJE21193 to replace them. I was unsure about one of the emitter resistors so I replaced both of those on the bad channel with the right .22 Ohm resistor. I checked the driver transistors and 2SA839 seemed to be questionable (Measured low), so I replaced the 2SA839 and 2SC1669 with MJE15033 and MJE15032. R601 (Labeled as R605, see story below) was open as well so I replaced that with a 10 Ohm 2 Watt resistor.
After I replaced the bad parts and there is still no click. I removed the 1193 and 1194 and now the channel that used to work doesn't. I removed ALL the outputs and still no click. I was wondering if someone could give me a direction to look. I have checked the upstream transistors from the drivers and none show shorted (Q505, Q507, Q509, Q513 and Q508, Q510, Q512, Q514). I checked the transistors on the protection board (All small signal ones) and they do not appear to have any shorts either. No fuses blown, and none of the parts get hot when the system is running. R822 ands R821 do get warm when the system has been on for a bit but not hot. Here are the voltage readings for the Output and Driver transistors. The tuner appears to work as do the lamps so the power supply board appears to be fine. I checked the yellow VCC power input on the protection/amp board and its 42 v (42.4 actually) as shown in the schematic.
You will see in my measurements below that the rail voltage is 47 and -47. The schematic says 54 and -54, but even when the one channel worked, before I starts changing parts, this was only 47 and -47. I downloaded the schematic / service manual from HiFi Engine and I am not sure how reliable this schematic is. For example, it shows R 601 is the resistor I replaced but it's labeled as R605 on the board. R601 has holes and a label on the board, but the leads go to a point of no connection. But R603 is in it's place and the opening for R607 (the compliment to R605) is empty. It's like this board was used in a couple different model of receiver and has open spots for other parts. I am guessing it was populated as required based on the model.
I took the output transistors out to check them and no shorts on those so, it does not appear that I blew them out. They seem to read properly on my meter in the Diode Check mode. I did the same with the drivers and they check out too. They don't show any shorts while in the circuit either when using the Diode Check function of my meter.
Outputs: ----------------
Q601: E 33.7 v
B 34.34 v
C 47.32 v
Q603: E 33.6 v
B 34.34 v
C -47.35 v
Q602: E 16.4 v
B 16.86 v
C 47.36 v
Q604: E 16.37 v
B 16.88 v
C -47.32 v
Drivers ---------------------
Q515: E 34.6 v
B 34.8 v
C 47 v
Q517: E 33 v
B 33.6 v
C -47.2
Q516: E 16.3 v
B 16.9 v
C 47 v
Q518: E 15.9 v
B 16.1 v
C -47 v
I ordered some MJE21194 & MJE21193 to replace them. I was unsure about one of the emitter resistors so I replaced both of those on the bad channel with the right .22 Ohm resistor. I checked the driver transistors and 2SA839 seemed to be questionable (Measured low), so I replaced the 2SA839 and 2SC1669 with MJE15033 and MJE15032. R601 (Labeled as R605, see story below) was open as well so I replaced that with a 10 Ohm 2 Watt resistor.
After I replaced the bad parts and there is still no click. I removed the 1193 and 1194 and now the channel that used to work doesn't. I removed ALL the outputs and still no click. I was wondering if someone could give me a direction to look. I have checked the upstream transistors from the drivers and none show shorted (Q505, Q507, Q509, Q513 and Q508, Q510, Q512, Q514). I checked the transistors on the protection board (All small signal ones) and they do not appear to have any shorts either. No fuses blown, and none of the parts get hot when the system is running. R822 ands R821 do get warm when the system has been on for a bit but not hot. Here are the voltage readings for the Output and Driver transistors. The tuner appears to work as do the lamps so the power supply board appears to be fine. I checked the yellow VCC power input on the protection/amp board and its 42 v (42.4 actually) as shown in the schematic.
You will see in my measurements below that the rail voltage is 47 and -47. The schematic says 54 and -54, but even when the one channel worked, before I starts changing parts, this was only 47 and -47. I downloaded the schematic / service manual from HiFi Engine and I am not sure how reliable this schematic is. For example, it shows R 601 is the resistor I replaced but it's labeled as R605 on the board. R601 has holes and a label on the board, but the leads go to a point of no connection. But R603 is in it's place and the opening for R607 (the compliment to R605) is empty. It's like this board was used in a couple different model of receiver and has open spots for other parts. I am guessing it was populated as required based on the model.
I took the output transistors out to check them and no shorts on those so, it does not appear that I blew them out. They seem to read properly on my meter in the Diode Check mode. I did the same with the drivers and they check out too. They don't show any shorts while in the circuit either when using the Diode Check function of my meter.
Outputs: ----------------
Q601: E 33.7 v
B 34.34 v
C 47.32 v
Q603: E 33.6 v
B 34.34 v
C -47.35 v
Q602: E 16.4 v
B 16.86 v
C 47.36 v
Q604: E 16.37 v
B 16.88 v
C -47.32 v
Drivers ---------------------
Q515: E 34.6 v
B 34.8 v
C 47 v
Q517: E 33 v
B 33.6 v
C -47.2
Q516: E 16.3 v
B 16.9 v
C 47 v
Q518: E 15.9 v
B 16.1 v
C -47 v
