Electronics

Michael Fiedler · Guest

I am working on this receiver for my son. No sound, except for a
little bleed through. I do get sound through the preamp and the phono
amp, so I know that part is working; however, the tuner is not
working. +12v line is 4.6v going to the tuner (and probably
everywhere else). I get 4.6v at the output of the positive 12v
regulator. The -12v regulator output is okay. It seems like there
are a lot of places the 12v could be shorted in this receiver. Has
anyone seen this problem, or if not, point me in the right direction?
I am kind of stumped right now. Thanks in advance for any help.

dkuhajda@locl.net · Guest

If the 12V line were being loaded down that much the regulator should
be so hot it will burn the skin off your fingers as soon as you touch
it.

If there is not excessive load then the regulator will not be so hot
and there is a problem in the regulator circuit somewhere.

Arfa Daily · Guest

Agreed. On many occasions, I have had these 7812 monolithic regulators, go
low output. 4 odd volts is about the level you do get out from them when
they do this. If the regulator is not red hot ie being loaded into thermal
shutdown by an external fault, just replace it.

Arfa

gb · Guest

Arfa
IF you decide to replace the regulator, check the capacitors on the input
and output pins (leakage, bulging, etc.) to the regulator -- good time to
replace these -
if problematic.

gb

Arfa Daily · Guest

Thanks for adding that gb, I should have said. You tend not to think to say
these things when you normally do it yourelf as a matter of course.

Arfa

Michael Fiedler · Guest

Thanks for the info. The resistors on the input side of the regulator
are a lot hotter than those on the input side of the negative
regulator. All caps (input and output) near regulator look normal,
although I need to take them out and check them on a checker. When I
resolve this issue fully, I will repost my findings for others.

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