I removed the AD823 to reset. No go, numbers just kept rolling. Then I noticed while I watched one of the leads fell off! The count kept going! I disconnected both leads and yes it kept going. I don't know what its measuring, but I do not think it is the bias. Some artifact? I measured a AAA battery and it read right. So That isnt my bias voltage I'm measuring, its just the multimeter. I measured the rails, 17.34 perfect and steady. Move it over to preamp outputs, just non stop climbing up and down.
I do not have a spare AD823 or other opamp. I will order a couple, it may be dead, but something else must be as well. The first fireup went like it was supposed to, near zero, install AD823. steady. I don't think the meter is showing offset, I think its just some odd load? What should I measure next assuming we are at the "fire up without AD823 stage" and the offset is wonky?
I do not have a spare AD823 or other opamp. I will order a couple, it may be dead, but something else must be as well. The first fireup went like it was supposed to, near zero, install AD823. steady. I don't think the meter is showing offset, I think its just some odd load? What should I measure next assuming we are at the "fire up without AD823 stage" and the offset is wonky?
Short IN/G on the channels to make sure its not open input noise making your offset indication dancing
Shorted the IN/G on both sides, no difference. It starts and goes higher and higher. Reading through looking for anyone with similar problems.
Saw someone on post # 4945 killed bias by improperly inserting an opamp. You were having him measure around J1,J2,Q1, and Q2. I havent read where he came back yet!
Saw someone on post # 4945 killed bias by improperly inserting an opamp. You were having him measure around J1,J2,Q1, and Q2. I havent read where he came back yet!
I don't think so, but anything is possible. I will message Teabag and see if there is a preamp board and parts for it. This one will go to salvage. I can't fix it, I'm not putting good money in this dead one, will start over with fresh board and parts. PS and I-select seem fine.
Russellc
Russellc
I have found Tea's site and have inquired. I see a full kit with PS and DCG3 with boards, but boards not available with the DCG3 parts kit.
May as well start with new board if possible, otherwise I will begin stripping components.
Russellc
May as well start with new board if possible, otherwise I will begin stripping components.
Russellc
Tea got back to me and is seeing what he has. Are there any tests to rare bits to see what is alive or not? with my luck I probably killed only those! If worst comes to worse it looks like there may be some full kits, hate to re buy what I dont need, but this thing must get built, extra parts not withstanding.
Russellc
Russellc
You could start by measuring Vgs for Mosfets (Vdc btween pins 1&3) 2-4V is good
Vbe for BC transistors (Vdc between pins 2&3) 0.55-0.7V is good
RDS (Ohms between pins D&S) for uPAs when the power is off. Should be in the tens or early hundreds of Ohms but not near short or in the kOhms.
Vbe for BC transistors (Vdc between pins 2&3) 0.55-0.7V is good
RDS (Ohms between pins D&S) for uPAs when the power is off. Should be in the tens or early hundreds of Ohms but not near short or in the kOhms.
To also check bias for the uPAs as set by the BF256B there should be 0.9-1.1V across R3 if it is a 220R. If it is a 150R 0.6V-0.75V.
On the upa, first one d to s = 73.2, other side of same upa =73.7. getting stuff out of way to measure other one. Volume pot in way so need to move.
Second one will be harder to measure, heat sink will have to be undone. Does 70ish readings Bode well?
