Sean Posted October 16, 2017 Share Posted October 16, 2017 (edited) I have an MXR M80 DI that I accidentally powered up with an 18v supply and it stopped working. It still sort of powers up and the LEDs come on but no sound. Can anybody tell me what the component is in the photo below? I measured the resistance across it and it's showing open circuit whereas an identical component elsewhere on the board is showing 18 ohm. Is this a power supply fuse? Text on there I can see is GW and IN4 but there's other text underneath that is a continuation of those. Any advice on what else to look for and how or whether this can be fixed? Edited October 16, 2017 by Sean Quote Link to comment Share on other sites More sharing options...
paul_5 Posted October 16, 2017 Share Posted October 16, 2017 1N400x (probably a 4007 or 4009) polarity protection diode. They're pence to buy and easy to replace. My worry is that if it's gone 'open circuit' then it's allowed 18v to go further than just that one component and could have potentially damaged something else. Quote Link to comment Share on other sites More sharing options...
Norris Posted October 16, 2017 Share Posted October 16, 2017 If it's a diode, have you checked it both ways? Swapped the positive and negative leads around? Diodes allow current one way but not the other Quote Link to comment Share on other sites More sharing options...
Sean Posted October 16, 2017 Author Share Posted October 16, 2017 I’ll check when I get home! Cheers guys. Will update soon Quote Link to comment Share on other sites More sharing options...
3below Posted October 16, 2017 Share Posted October 16, 2017 It appears to be a diode IN40xx [url="https://en.wikipedia.org/wiki/1N400x_general-purpose_diodes"]https://en.wikipedia.org/wiki/1N400x_general-purpose_diodes[/url] They can be used as a protection method against incorrect polarity connection. The one schematic I can find shows this as D3 - a protection diode. Testing components that are in circuit can give erroneous results - I would expect the diode to show zero resistance in the foward mode and infinite in the reverse bias mode. The 18 ohms you measure with the other diode could be a side effect of the remainder of the circuit. It can be desoldered with a 'solder sucker' or braid. Component costs pence. Easy DIY job, it may be the cause, it may not. Schematic here, the only one I can find - you will have to endure the free trial [url="https://www.scribd.com/doc/73304672/MXR-Bass-DI#"]https://www.scribd.com/doc/73304672/MXR-Bass-DI#[/url] Quote Link to comment Share on other sites More sharing options...
Sean Posted October 17, 2017 Author Share Posted October 17, 2017 [quote name='Norris' timestamp='1508180776' post='3390341'] If it's a diode, have you checked it both ways? Swapped the positive and negative leads around? Diodes allow current one way but not the other [/quote] Yes. It reads 18 ohm in the one direction, off the scale in the other. WOuld that indicate that the issue is elsewhere? Quote Link to comment Share on other sites More sharing options...
Norris Posted October 17, 2017 Share Posted October 17, 2017 [quote name='Sean' timestamp='1508240364' post='3390719'] Yes. It reads 18 ohm in the one direction, off the scale in the other. WOuld that indicate that the issue is elsewhere? [/quote] Yes - you need to keep looking Quote Link to comment Share on other sites More sharing options...
MoonBassAlpha Posted October 18, 2017 Share Posted October 18, 2017 That's a power diode , probably 1n4148, I'm guessing to protect against reverse polarity on the power supply Quote Link to comment Share on other sites More sharing options...
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