Leach problems

peter5

Member
2001-06-04 5:09 am
I'm still working on my two-channel Leach Amp because I've been running into several unfortunate problems. I'm hoping somebody can help me with the latest problem because I'm completely stuck. When I connect my speakers to the binding posts all of my output transistors are shorted between emitter and collector. My ohmeter reads about 2 mega-ohms. Is this supposed to happen? When I disconnect the speakers the transistors aren't shorted anymore. I've checked all of the resistors and transistors on the board and they are all fine. Any help would be much appreciated.

Thank you for your time.
Peter
 

peter5

Member
2001-06-04 5:09 am
I have the amp turned off and the speakers connected. I tested the resistance between the emitter and the collector. None of the transistor collectors are shorted to the heatsink. When the ground is disconnected from the negative terminal the transistor leads aren't shorted anymore.
 

blmn

Member
2001-02-01 2:43 am
.
Peter

It was not entirely clear for me, but,I guess you must check the idle current of the output devices (and the components wich take care of it), as well if they are oscillating. It seems to be instability.

When the amp is powered on without load, what happens?

blmn
 
Ist: make sure that no shorts are between the Col of each output transistor and ground. with your speaker disconect. if all is well then connect a 100 watt AC lamp in series with the AC mains. the lamp should glow bright as the Ps caps charge up then go Dim. set bias to min pos full CC in this amp. If the lamp dose not dim remove power and futher investigate.