DC-DC mod query
Posted: Thu Apr 11, 2024 6:13 pm
I have an issue 3 board which has a faulty 12V supply (reads a wobbly +1.2V). -5V works correctly.
I've never tried to fix a DC-DC problem before, so I thought I'd start from first principles. The board has had a DC-DC mod of some sort, so I've had a good look at it and taken notes. Here's an annotated image:
I was following the modification described here. The mod on my board seems similar, but not quite the same. In particular, the 2 hand soldered diodes I've marked with green dots don't seem to correspond to anything in the documented mod. Do I misunderstand, or is this a variant with a couple of extra diodes?
I'm not quite sure how to proceed. I could just dismantle this lot. I think I might have to because I can't physically get to TR4 and TR5 in order to test or replace them. Nothing moves or bends! I can feel with a fingertip that one of them gets hot. On the other hand, most of this seems to be related to the -5V supply which is working fine, so I don't really want to pull it all apart if that's not necessary.
Advice please?
I've never tried to fix a DC-DC problem before, so I thought I'd start from first principles. The board has had a DC-DC mod of some sort, so I've had a good look at it and taken notes. Here's an annotated image:
I was following the modification described here. The mod on my board seems similar, but not quite the same. In particular, the 2 hand soldered diodes I've marked with green dots don't seem to correspond to anything in the documented mod. Do I misunderstand, or is this a variant with a couple of extra diodes?
I'm not quite sure how to proceed. I could just dismantle this lot. I think I might have to because I can't physically get to TR4 and TR5 in order to test or replace them. Nothing moves or bends! I can feel with a fingertip that one of them gets hot. On the other hand, most of this seems to be related to the -5V supply which is working fine, so I don't really want to pull it all apart if that's not necessary.
Advice please?