04-12-2016, 03:12 PM
Thanks for your support Mark. I'm puzzled now, the amp seems to be working ok??
Yesterday I got in a right mess trying to trace out the circuit around Q3. I had an stupid attack and got confused by mixing up R22 and R25 and tried to trace connections that wern't there. Spent hours chasing my tail.
This morning after reading your posts last night I thought I'd try to nail down the readings for Q3. I rechecked the pinout for the BD235 ( no wonder I get confused what with some types being EBC others ECB and others BCE) and took readings which are good LH = E -1.8v C 1.8v B - 1.2v bad RH E -1.5v C 1.9v B - 1.3v . I then got a screw driver and turned R22 (VR1) fully CCW/CW on the iffy CH a few times to see what voltage range was present on Q3's base, I got 1.7v to 2.2v. I then set it to 1.2v, same as the LH CH, rechecked readings and got the same as the LH CH.
I the swapped the pre-amp cards to see if the fault follwed the cards to see if I could narrow the fault down. Started the amp expecting one to shut down/overheat, was still waiting 30 mins later. So I put a a signal in cranked both up to 160w both remained ok,. Puzzling. I rechecked both were at 300mV, all seems well.
I wonder if rotating the pot has jiggled something loose if see what I mean. I'll re test tommorow.
Cant understand why Q3's voltages don't match those you mentioned yesterday. I'll take some good pics tommorow and post more data. Being Sunday bit pushed for time.
Cheers, A.
Yesterday I got in a right mess trying to trace out the circuit around Q3. I had an stupid attack and got confused by mixing up R22 and R25 and tried to trace connections that wern't there. Spent hours chasing my tail.
This morning after reading your posts last night I thought I'd try to nail down the readings for Q3. I rechecked the pinout for the BD235 ( no wonder I get confused what with some types being EBC others ECB and others BCE) and took readings which are good LH = E -1.8v C 1.8v B - 1.2v bad RH E -1.5v C 1.9v B - 1.3v . I then got a screw driver and turned R22 (VR1) fully CCW/CW on the iffy CH a few times to see what voltage range was present on Q3's base, I got 1.7v to 2.2v. I then set it to 1.2v, same as the LH CH, rechecked readings and got the same as the LH CH.
I the swapped the pre-amp cards to see if the fault follwed the cards to see if I could narrow the fault down. Started the amp expecting one to shut down/overheat, was still waiting 30 mins later. So I put a a signal in cranked both up to 160w both remained ok,. Puzzling. I rechecked both were at 300mV, all seems well.
I wonder if rotating the pot has jiggled something loose if see what I mean. I'll re test tommorow.
Cant understand why Q3's voltages don't match those you mentioned yesterday. I'll take some good pics tommorow and post more data. Being Sunday bit pushed for time.
Cheers, A.
