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Quoted from Lowaek:Hoping someone can help identify the value of R4 on this old Marco rectifier?
Can you read the color code off the resistor?
I cannot zoom in enough to tell what it is. Is it yellow/yellow/yellow/gold?
if so, then it's 440 kΩ +/- 5%. It looks small, like ¼-watt size, but that is hard to tell from photo.
Quoted from Quench:The thickness and density of the carbon band tells me it's a medium value resistor. With nearly 240VDC across it and being a low wattage resistor, it's no wonder it cooked.
Quoted from Quench:Might be a 2 watt resistor.
Presuming it's a series resistor with the "230VDC Displays" LED indicator:
230V / 39000Ω = 0.0059 amps
230V * 0.0059A = 1.36 Watts power consumption
Excellent presumptions. Also, now looking at the silkscreening on the PCB, the white rectangle that outlines R4 is huge compared to the other resistors.
Quoted from Quench:The soldering on that burnt resistor doesn't look original - maybe it's been changed with a wrong (low wattage) part at some point.
Exactly. The white square is so large the original has to be at least 2-watts, as you already stated.
Quoted from G-P-E:I would actually go to a 5W resistor for that one but fitting one physically that big would be tough.
Is there enough physical room to fit two 2-watt resistors in parallel? Effectively giving you a 4-watt capacity. Of course, each one would have to be double the resistance rating.
Quoted from balzofsteel:Probably. You might have an issue with getting all the leads through the board holes.
If the pads are large enough, drill two more holes.
Quoted from balzofsteel:A 5w metal oxide should fit. At worst bend one lead and stand it on end like in an old transistor radio.
Yes, or do that. That would also give more clearance for air flow.
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Manhattan, IL