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Jan. 27th, 2018
electronics
Jan. 27th, 2018 05:11 pmI wrote on Facebook earlier today...
This schematic is making less sense as I go...
I think there may be wrong connections. This is the kit version of the meter, which means someone wired it up at home. I'd love to know what that person was like. Was he someone very much like me, fifty or sixty years ago?
That said, I'm pretty sure there isn't suppose to be AC on four out of five of the anodes in the vacuum tubes. But maybe I'm wrong. Onward with circuit mapping...
But I've found elements that look familiar from schematics I have. I found the zero balance pot, for example, right were it's supposed to be between two resistors attached to the anodes in the 12AU7 tube. Hopefully if there are errors, they won't be too egregious.
---
Just now, though, I checked the internet and found that you number IC pins from a top view, but tube socket pinouts are read as if from the bottom. I was reversing everything! Suddenly it becomes clear! I was looking at my drawings and thinking "You know, connections seem to have the right patterns, but be connected to the wrong pins. Wait a minute..."
This schematic is making less sense as I go...
I think there may be wrong connections. This is the kit version of the meter, which means someone wired it up at home. I'd love to know what that person was like. Was he someone very much like me, fifty or sixty years ago?
That said, I'm pretty sure there isn't suppose to be AC on four out of five of the anodes in the vacuum tubes. But maybe I'm wrong. Onward with circuit mapping...
But I've found elements that look familiar from schematics I have. I found the zero balance pot, for example, right were it's supposed to be between two resistors attached to the anodes in the 12AU7 tube. Hopefully if there are errors, they won't be too egregious.
---
Just now, though, I checked the internet and found that you number IC pins from a top view, but tube socket pinouts are read as if from the bottom. I was reversing everything! Suddenly it becomes clear! I was looking at my drawings and thinking "You know, connections seem to have the right patterns, but be connected to the wrong pins. Wait a minute..."
Well crap. Now that I know I had the pins backward, I know why the fuse on the primary side of the transformer was blown. The secondary winding powering the tube heaters is shorted out. And the fact that someone jumpered around the fuse means they probably tried to turn it on again without fixing the underlying issue and may have fried more stuff. On the plus side, this thing doesn't have any ICs to kill; it may well all be stuff I can replace.
Assuming I can find a new transformer....
I'm going to give it a good try, but this may end up being a parts machine if I can't. I'll confirm the issue at home by desoldering the secondary outputs and checking continuity across them.
Assuming I can find a new transformer....
I'm going to give it a good try, but this may end up being a parts machine if I can't. I'll confirm the issue at home by desoldering the secondary outputs and checking continuity across them.
