Quote:
Originally Posted by zeno
Hint for hidden fuses.
This is more for the beginner. We used to get quite a few cheapo
Jap stereos & other smalls with open primary on power transformers.
After a few years I was working on one & saw a fuse INSIDE the transformer
on the schematic. We found many had one but was almost never in the
schematic or noted inside the rig anywhere. Dont remember any US
made stuff that way but keep it in mind.
BTW almost never changed a transformer after that.
73 Zeno 
LFOD ! |
Very common on the Japanese stereos. Here's a hint for those who haven't seen this: the primary will read open, and if you look at where the AC input is on the XFR, you will see a third terminal unoccupied. This is generally the tie point for the internal fuse, which is **thermal in nature. Jumping the center terminal to the appropriate AC terminal would restore operation.
For our personal stuff, we used to just jump them out. Never saw a single incident where a short in the stereo blew the fuse, and never saw a bad transformer either. My guess is that they would just fail from many thermal cycles over the years.
**Regarding the thermal fuse, it may have been a Japanese certification requirement. It's hard to imagine a scenario where a short or incorrect load in the stereo would cause overheating of the transformer to the point of being a fire hazard and yet not blowing either the secondary or AC input fuse. Maybe it was required in Japan for anything with a socketed fuse that might be intentionally jumped out (?).
John