Yorkville 100watt Mixer/Amp - Replaced Transistors

[Jason G]

Also, i have 2 brand new MJH11021 and MJH11022 trans. I tested the new ones and compared with the current ones (in circuit) I got some dissimilar readings which i assume is due to the current ones being in circuit. Readings over 1.5xxx or in some cases start at 1.5 then go down to 1. not sure if that could mean anything or if its a fair test.

thanks!

 

[Jason G]

Tests of QA5 and QA6 while done in PCB (hooked up)


QA5 Diode Test



B (black lead) to E (red lead) -> 0.777
B (black lead) to C (red lead) -> 0.770



C to E -> 1

E (black) to C (red -> 1.59



QA6 Diode Test



B (black lead) to E (red lead) -> 0.767
B (black lead) to C (red lead) -> 0.757



C to E -> 1

E (black) to C (red) -> 1

 

[kellys_eye]

The TO92 packaged devices are notorious (in my experience) for not having the pinouts you expect - often the base wire is at one side, collector in the middle etc.

Best solution would be to purchase anew BC550 and test its pin out before fitting it.

If the 'replaced' BC550 has been inserted incorrectly it is likely toast now and re-fitting it is pointless.