Euro PSU

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welhamc
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Euro PSU

Post by welhamc » Fri Feb 28, 2020 4:29 pm

I'm having an issue with a build of a eurorack PSU. The +12v and +5v rails are all working as expected, but the -12v rail is reading as -24v. I have checked that all the components are correct (including R7 and R9) and there are no dry solder joints. When I first powered the module there was a short that I had not seen between pins 2 and 3 of the LM337 so I am guessing that I have fried the chip... is there anything else it could be? I don't have a spare LM337 to hand but have one ordered to test this

Chris
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Synthbuilder
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Re: Euro PSU

Post by Synthbuilder » Sat Feb 29, 2020 5:28 am

It could be that D11 is around the wrong way, or maybe even dead. But given that the LM337 had its input and output shorted together for a even a short while, it is likely that the LM337 will need replacing.

Tony
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welhamc
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Re: Euro PSU

Post by welhamc » Mon Mar 02, 2020 4:27 pm

No luck swapping out for a new LM337. I also swapped out D11, the NEG trimmer and R7 and R9 and checked all the diodes - still getting around -23v on the -12v rail

I have an LM337BT instead of an LM337T - is this an issue?
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welhamc
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Re: Euro PSU

Post by welhamc » Mon Mar 02, 2020 5:08 pm

The voltage on pin 1 of u3 is around -24v whereas on pin 1 of the LM317 its is +11v - it seems that the problem is further upstream than the lm337 but cannot find anything obvious on the board..
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welhamc
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Re: Euro PSU

Post by welhamc » Mon Mar 02, 2020 5:16 pm

All working now! The problem was D13... it must've been fried when the LM337 was shorted but replacing it has given me -12v on the negative rail at last
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Synthbuilder
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Re: Euro PSU

Post by Synthbuilder » Tue Mar 03, 2020 3:54 am

welhamc wrote: ↑
Mon Mar 02, 2020 5:16 pm
 All working now! The problem was D13... it must've been fried when the LM337 was shorted but replacing it has given me -12v on the negative rail at last
That's good to hear that you got it working. I'm completely puzzled why D13 took a hit though. I wonder whether both the first LM337 and D13 got killed with the original short.
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