24 Aug
2014
24 Aug
'14
7:01 p.m.
On 8/24/2014 9:43 AM, Chuck Guzis wrote:
On 08/23/2014 11:30 PM, Josh Dersch wrote:
Success: http://yahozna.dyndns.org/scratch/interact/WP_20140824_003.jpg
Ran out to a local electronics parts place and replaced the 7805 this
afternoon, and it powered right up. Now to rebuild the cassette drive
(needs a new belt or two...)
Thanks for the assistance!
- Josh
Thanks! Lifting CR22 (which took awhile to find,
it's actually clear on
the other side of the PCB from the rest of the supply) made no
difference in behavior.
Removing IC 63 (which is a 7805, nice guess) and reading voltages on the
positive lead of C67 yields about 15VDC. The resistance between the +5V
lead of the IC63 socket and ground is about 3.5K ohms, so it doesn't
look like there's a dead short here. Would the 7805 be a likely suspect
here? Any easy way to test it?
Just replace the 7805--they should be common as dirt. Since it's a
power IC and can run very warm, it's not uncommon to have a failure
there. particularly when dissipating most of your power input as heat!
I assume that thing doe shave a heat sink. If not, it might be
prudent to install one.
The resistance of the +5 line to ground is certainly well within what
I'd expect.
--Chuck 