? Fixing Burned Flatbed Scanner Power Resistor

[Franc Zabkar]

On Tue, 26 Aug 2008 17:45:08 -0400, "Alec S." <nospam@127.0.0.1> put
finger to keyboard and composed:

Do you suppose it could be capacitor plague? It is only slightly bluging at the
top; it doesn’t seem to have vented at all. Here’s a closeup of the cap:
http://img388.imageshack.us/img388/6310/img3590qt9.jpg

I don't understand why you are having such a hard time of it. You have
measured a dead short at the input to the regulator. Desolder the
regulator's input pin and test for a short again. If the short remains
after desoldering the regulator, then desolder other connected
components until the short goes away. The last component will be your
culprit.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[Franc Zabkar]

On Fri, 22 Aug 2008 09:13:35 +0100, "Arfa Daily"
<arfa.daily@ntlworld.com> put finger to keyboard and composed:

Once you are past the
regulator, you're into the realms of faulty LSIs ...

If you look at the print around L5, there are at least two sections of
the PCB that see the full unregulated input. IMHO that's potentially a
big concern, although it could be just supplying the motor(s) and
lamp.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[Franc Zabkar]

On Tue, 26 Aug 2008 13:37:51 -0400, "Alec S." <nospam@127.0.0.1> put
finger to keyboard and composed:

Yes it does. I’ve posted an overhead shot of it here:
http://img204.imageshack.us/img204/5918/img3570nz1.jpg The resistor goes from
the + terminal to the input pin on the 7805, apparently passing through an SMT
resistor or something (B32—is there a site with a list of standard PCB text
identifiers?)

I suspect that B32 is a ceramic (b)ypass capacitor connected between
the input and ground pins of the regulator.

In a similar fashion, B24 appears to bypass the unregulated +12V
supply to ground after it passes through L5.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.