TAC Scorpion power supply - 2W resistors

[magicwand]

I am rebuilding an old TAC Scorpion mixing console power supply - full re-cap and new volt. regulators.

While working, I noticed these resistors and thought I would go ahead and measure their values.

The schematic I found lists R3, R4, and R5 as 1 Ohm, 2.5 Watt. That schematic is located here: TAC PSU Schematic. (a note about this - my PCB is labeled JP294B on the underside and other than these resistor values, I haven't found a difference between my board and that schematic)

Anyway, all three of the above resistors test out at .5 Ohm. If I have the correct schematic, that is wrong.

Additionally, I noticed a slight discoloration on the underside of the PCB:

Are these guys in need of replacement? These are wirewound type, correct?

Thanks!

 

[Mark Tillotson]

Did you measure them in circuit? If so you'd expect 0.33 ohms plus whatever your lead resistance is, which could easily be an extra 0.2 - they are in parallel. They are fired ceramic wirewound, bombproof to heat damage I'd have thought - the PCB would char heavily first...

 

[magicwand]

Ah, I see. I measured in circuit. There are additional current paths because they're in parallel, reducing the ohm reading on my multimeter.. I guess it surprises me that the leads would add that much resistance, but i've really learned something here, thanks!