01-16-2015, 09:55 PM
I finally got back to the main amplifier board.
I removed and tested all the power transistors.
All 4 are giving me a reading btwn. E&C only one way. Example: Positive lead on E neg. on C. the other way around I get no reading I guess I cooked them. All the other tests read like a good transistor should. The old ones test good except for one.
I decided to use two of the old good ones and rebuild one side of the amp.
I replaced C 9,10,-100P C15,16- 47P C17,18,- 0.022, C19,20, 100P.
Tested the transistors and Q6 2sa497 was bad. Replaced it and Retested all the resistors. Replaced R30 ,150 ohm.
Hooked up the amp on the rebuilt side, its the (out 2) side of amp. with jumper wires. connected as follows:
E2,E4, out2, in2, and B+ and a ground jumper wire from the mounting bracket to chassis. All wires on power board hooked up.
Speaker plugged into A socket on back of receiver.
It powered up fine and at 115v it was drawing only .1 amp. Which I believe is good.
Problem is I only get a steady medium hum out of speaker that does not change with Vcontrol. I plan to order another power transistor and finish side 1 of the amp.
The lightes all work and changing dial scale you can see the signal strenght meter respond to where radio stations are.
Not sure what I can check with one side of amp. only hooked up.
Any guidance appreciated. Whew!
I removed and tested all the power transistors.
All 4 are giving me a reading btwn. E&C only one way. Example: Positive lead on E neg. on C. the other way around I get no reading I guess I cooked them. All the other tests read like a good transistor should. The old ones test good except for one.
I decided to use two of the old good ones and rebuild one side of the amp.
I replaced C 9,10,-100P C15,16- 47P C17,18,- 0.022, C19,20, 100P.
Tested the transistors and Q6 2sa497 was bad. Replaced it and Retested all the resistors. Replaced R30 ,150 ohm.
Hooked up the amp on the rebuilt side, its the (out 2) side of amp. with jumper wires. connected as follows:
E2,E4, out2, in2, and B+ and a ground jumper wire from the mounting bracket to chassis. All wires on power board hooked up.
Speaker plugged into A socket on back of receiver.
It powered up fine and at 115v it was drawing only .1 amp. Which I believe is good.
Problem is I only get a steady medium hum out of speaker that does not change with Vcontrol. I plan to order another power transistor and finish side 1 of the amp.
The lightes all work and changing dial scale you can see the signal strenght meter respond to where radio stations are.
Not sure what I can check with one side of amp. only hooked up.
Any guidance appreciated. Whew!