Well... without the zeners, the voltages are very high as I mentioned before, and worst of all, they are always negative (-4.5v) and I can not modify this reading by adjusting VR502 or 501.
The only different readings I found where:
On TR509 base I have -3.7v
On TR505 collector I read +2.6v.
None of these values could be modified by turning the VRs.
Now I soldered the zeners and also replaced D511 and D514 by new diodes as you indicated.
The situation is the same again.
+0.3v NPN -0.5V PNP.
These values can be altered by turning the VRs, but the relative difference is the same (not simmetrical).
I am suspecting the readings I get on TR551:
B -1.1v ok
E -1.8v (should be -1.7v)
C 1.63v (should be 1.75v and I can adjust it but emitter gets too high at -1.93)
Can this be the source of the differences found on the bases ?
Regards
Ricardo
The only different readings I found where:
On TR509 base I have -3.7v
On TR505 collector I read +2.6v.
None of these values could be modified by turning the VRs.
Now I soldered the zeners and also replaced D511 and D514 by new diodes as you indicated.
The situation is the same again.
+0.3v NPN -0.5V PNP.
These values can be altered by turning the VRs, but the relative difference is the same (not simmetrical).
I am suspecting the readings I get on TR551:
B -1.1v ok
E -1.8v (should be -1.7v)
C 1.63v (should be 1.75v and I can adjust it but emitter gets too high at -1.93)
Can this be the source of the differences found on the bases ?
Regards
Ricardo
An externally hosted image should be here but it was not working when we last tested it.
Here you have some pics.... latter I will post the underside.
Regards
Ricardo
regarding TR551 is ok, those values are normal.
But +0.3v NPN -0.5V PNP - this situation isn't good. Can you check trimmers, try to adjust same as on working amplifier. Measuer resistance and them solder back.
check VR501 values, most of th times old trimmers and electrolytes are nr.1 troublemakers. It will be very good if you have new ones to replace, or other but in good condition.
VR502 trimmer will be good to desolder from good amp measure and make same in bad amp and, don't touch it until you get good voltage in base of out trannie..
Sorry, man I cannot se much from your picture, if you have higher resolution, please send it my email.
But +0.3v NPN -0.5V PNP - this situation isn't good. Can you check trimmers, try to adjust same as on working amplifier. Measuer resistance and them solder back.
check VR501 values, most of th times old trimmers and electrolytes are nr.1 troublemakers. It will be very good if you have new ones to replace, or other but in good condition.
VR502 trimmer will be good to desolder from good amp measure and make same in bad amp and, don't touch it until you get good voltage in base of out trannie..
Sorry, man I cannot se much from your picture, if you have higher resolution, please send it my email.
Just replaced 47k trimmer but the difference persists.
As the amp seemed stable, I installed only two output trannies and the amp is working.
I am hearing it trough a woffer speaker without enclosure and using a walkman in the input so I can not tell if the sound is good.
I do not seem to notice any distortion.
I have not been able to make the output trannies bases voltages simmetrical... (+0.47 NPN -0.67 PNP).
I read 70mv in the speaker terminals.
I have readings between 1 and 7mv on points TP (34) when music is playing.
Can I assume the unit will not distort and solder some more trannies ?
Thank you for time and help.
Regards
Ricardo
As the amp seemed stable, I installed only two output trannies and the amp is working.
I am hearing it trough a woffer speaker without enclosure and using a walkman in the input so I can not tell if the sound is good.
I do not seem to notice any distortion.
I have not been able to make the output trannies bases voltages simmetrical... (+0.47 NPN -0.67 PNP).
I read 70mv in the speaker terminals.
I have readings between 1 and 7mv on points TP (34) when music is playing.
Can I assume the unit will not distort and solder some more trannies ?
Thank you for time and help.
Regards
Ricardo
RCruz said:
Listen,
You have to make it symetrical voltages in out tranies otherwise will not work fine.
Regarding adjusting idle corrent and neutral point voltage, you have to do according to service manual, otherwise you didn't complete the task.
Ric, it can work maybe some weeks and will pop again, therefore you've to try and do more fixing, see any "bad" soldier or similar, or check the drivers, might be one which is releasing 0.67 might have current leaking. And if you are asking me how to check for that, you should have an device which check trannies called atlas. The cheapest way is just put another trannie there and see for difference, if not put it back.
bekim said:
Listen,
You have to make it symetrical voltages in out tranies otherwise will not work fine.
Regarding adjusting idle corrent and neutral point voltage, you have to do according to service manual, otherwise you didn't complete the task.
Ric, it can work maybe some weeks and will pop again, therefore you've to try and do more fixing, see any "bad" soldier or similar, or check the drivers, might be one which is releasing 0.67 might have current leaking. And if you are asking me how to check for that, you should have an device which check trannies called atlas. The cheapest way is just put another trannie there and see for difference, if not put it back.
Thank you again....
Last night I soldered more two trannies and after power on, all trannies blew instantly.
Back to the start again......
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