Can you show a picture where you measured that, just to be sure we are on the same page.I get 56 and 57.2 v, I am on DBT with this guy again as I have new outputs and trimmers installed and would prefer to remain cautious.
Yes. Here and here on other side. Neg on DMM to chassis ground.
That's the spot. Definitely should not have 50+ volts there. My thoughts are that if both channels have the same issue then perhaps you are missing a power supply voltage.
I have my -58.9 and 58.9 at the main filter caps and -61v at 2 points of the driver board and 56-58 at others. I will look over the schematic and do some poking around.
That sounds correct. Pull the driver board and power it up and check the offset voltage at the protection board again. Should be zero.
I am relatively new to this, but should you be checking DC offset across your emitter resistors? That would mean you are measuring a drop in voltage across those resistors rather than the amount of voltage present at the outputs (in this case, let's just say the outputs before they reach the speaker switch or the protection relay). In situations like this, I just test for DC at the output at the point where the signal enters the protection board. Maybe I am misunderstanding something. In any event, when I have excessive DC offset, I start by replacing the differential pair at the input of the driver board (TR1,2,3,4).
We all go through these thought gyrations, but actually writing out what you are thinking can be helpful to others, it can stimulate the thought processes of someone with a problem. Sometimes this is enough to simply help someone's understanding, and sometimes it leads directly to a solution.
Offset is showing zero with the driver board pulled.
I hope not! Here are some better pics. The transistor orientation for that pre driver are the inverse of each other.Thanks for the pictures. I see a couple of things.
Could be the light or the angle but those resistor leads may be touching?
The other blue box. (should have made it red) Pretty sure you have that transistor oriented wrong.
View attachment 3609986
On the first picture you have two spots circled and on the second picture you show one wire. I think the black wire comes from the unlabeled pin, correct?
My board layout shows them as 180 degree opposites. Comparing to the schematic the service manual board layout is wrong for TR02. It should be the same as TR01 BCE from top to bottom. So you are good to go.
Sorry it was too early and I wasn't thinking, I'm not sure why I thought that second picture was relevant here, it's two grounds that I had to desolder to get a better look at the protection unit.
Oh geez, that is confusing.
There are lots of well know and documented errors in service manuals. This may be/probably is one of them? I don't have much under the hood time with the DB versions of these.
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