While repairing a Marantz amplifier using the service manual, I came across resistors with odd symbols (see page 18). They are trapped between two parallel lines (for example, 3297).
Is this linked to the fact that this is a 0.33W resistor? A comment suggested it could be related to the way it's mounted to the board for heat dissipation, but I don't see any mounting difference between 3297 and 3283 (see picture below).
Furthermore, what's the difference between the "R" and "E" letters for 3293 & 3305. Don't they both mean "Ohm" ? Is there any reason for Marantz to use both notations in this diagram or is it just an inconsistency?
Answer
I came across resistors with odd symbols (see page 18). They are trapped between two parallel lines (for example, 3297).
(Crop from the original schematic, showing the unknown resistor symbol.)
Answer: That is one of the (many) symbols used for a fusible resistor. Here is an extract from page 177 in the book: Electronics for Service Engineers by Joe Cieszynski and David Fox (Google Books link to page 177) showing that symbol, which I've marked in red below:
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