Sequential circuits samplers

I went to Radio Shack today and was able to get a few of the ICs to
replace 7812 & 2x 7805.  There seem to be quite a number of variations
of this chip (I think), but it looks as though they all do the same in
the end and the ampere rating is well above the 500 mA that the
Prophet uses.  So out of the 4 on the bottom board, I replaced 3
(because I couldn't find a 7912) and the prophet still does the same
thing.  

I also check the boards for continuity since there appeared to be some
lifted traces but I was wrong.  My knowledge in electronics repair is
limited so I have no further ideas of how to fix this.  I ordered a
7912, but it seems very unlikely that the one IC that I couldn't find
to replace would be the one causing the problem.

By the way, I know the transformer and everything before it is good
because if I disconnect the transformer from the main board and turn
the machine on, then it does not blow the fuse.

Thanks,
Chase 


--- In prophet2000@yahoogroups.com, "duncan" <ferrograph@...> wrote:
>
> >>Any other suggestions?<<
> 
> yeah- the series regulators that provide the 5V & 12V rails into the
> rest of the instrument. 78xx & 79xx devices- these are the things you
> see fastened to the back of the case inside, probably with what looks
> like toothpaste (thermally conductive paste, in fact) around them.
> these things (78xx, 79xx) frequently fail in older gear.
> 
> you need to get a tech in there, with a voltmeter. your p2k may be
> perfectly alright once these are replaced & working again. but you've
> reached, with the greatest of respect, the limit of what you can do
> without a voltmeter & some component-replacement chops.
> 
> hth-
> duncan.
>