Musical Fidelity e300 power amp trannys help :(

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#21
just desolder one good output and measure is it bipolar transistor ;

then we'll know more

also - look are these small BC (or MPSA) cooked transistors - actually zenner followers for stabilization ?

in that case - bigger resistors and bigger transistors ; any darlington .... BDX53 and BDX54 , for instance
 
#26
I am not in the habit of giving misleading information. I have repaired a number of these units, mixed 150 and 300. They are the same, exept in the amount of output devices.
As you can see, the pc board is charred from excessive heat dissipation. It would be in your best interest to replace the components in that area as well. There is some discrepancy between the schematic, and the actual value of the components. I seem to recall that there are two resistors with the value of 1K. Uprate these to 1-2W. Also replace the four small signal transistors in the area. Leave the legs as long as possible, it will help dissipate heat.

Regards
Roar
 
#29
bias

thanks to all the helpful people here ive sourced the parts and am very close to having rebuilt it all. stripped it down ,cleaned and replaced any thermally damaged parts and tested eveything.

one more question guys, will i need to reset the bias? is there a good method to do this ?
thanks again
 
#30
2sd669a 649a

well after repairing my amp i was measuring volt drop across the emitter resistors ,slipped with probe and have damaged the above i think they are 2sd669a and 2sd649a .
can anyone suggest an equivalent cant find these anywhere....

thanks again
 
#32
well actually i shorted out a link in the board to the end of a the resistor i was measuring across - serves me right for trying to adjust bias and hold two probes at same time - should have found some croc clips !
thanks again- what do u normally set the bias at in the repairs u have done?
 
#35
Generally, I share what circuit diagrams that I have. However, diagrams given to me in confidence, I do not share. I do most repair on MF in Norway on behalf of the importer, so I can not give you the diagram. I can, however, help you with advice.
I once gave up a ML diagram with the agreement that it were for his eyes only, and to guide him with the repair of his amp, only to find it on display on a rather well known danish site. I didn`t like that.

Regards
Roar
 
#36
thanks

totally understand, not a problem.

will try and find some of those toshiba devices you suggested on monday and see how i get on.

the amp seemed to working perfectly until i caused the short .

silly me.

thanks for your time and advice
 
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