Hi,
I'm fault finding on this preamp effects units power supply, i have found a faulty 12v power regulator. the previous owner tried replacing the original regulated 9vac wall power supply with a 9vdc switch mode ps.
what is confusing is i'm reading very close to 25vdc at the input pins of the 12v regs. I would think i should be seeing about 14vdc from ground to each input reg pin?
the 7805 5v reg has 12vdc at the input and is output fine.
C167 and C168 are rated for 25v max.
is it likley a cap has shorted or something and the fault is is back feeding the rectifier diodes creating some sort of voltage doubler/ increase?
I'm fault finding on this preamp effects units power supply, i have found a faulty 12v power regulator. the previous owner tried replacing the original regulated 9vac wall power supply with a 9vdc switch mode ps.
what is confusing is i'm reading very close to 25vdc at the input pins of the 12v regs. I would think i should be seeing about 14vdc from ground to each input reg pin?
the 7805 5v reg has 12vdc at the input and is output fine.
C167 and C168 are rated for 25v max.
is it likley a cap has shorted or something and the fault is is back feeding the rectifier diodes creating some sort of voltage doubler/ increase?
Thankyou for the advice that is very good to know. I think it is only 7812 at fault then. the input pin is causing the input voltage to drop to 8vdc when connected i will get a replacement tomorrow. I am surprised the 25v caps has lasted at such a close limit voltage since 1996.
the transformer i have has a 7v tap as well, it is supplying 19vdc and 8.9vdc to regs so should be better for the regs and caps.
the transformer i have has a 7v tap as well, it is supplying 19vdc and 8.9vdc to regs so should be better for the regs and caps.
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