blown board snaffu, where to start ?
 

this is the board where the 32 V line shorted with 5V line at the
green ribbon connector near transformer and only blew center
busman fuse . i get continuity between 5v and 0V ref and now i
need some advice where to start looking for problems or some
methodology on what to do (pull ICs, etc)

and of course no schematic, i am trying to map the power section
now

thanks for any help,
robb

blown board snaffu, where to start ?
 

On Tue, 6 Nov 2007 07:25:01 -0500, "robb" wrote:

this is the board where the 32 V line shorted with 5V line at the
green ribbon connector near transformer and only blew center
busman fuse . i get continuity between 5v and 0V ref and now i
need some advice where to start looking for problems or some
methodology on what to do (pull ICs, etc)

and of course no schematic, i am trying to map the power section
now


Pull connectors. Repeat 5-0V z test at both ends.

On the end with zero ohms:

- Is there anything that looks like a zener or crowbar across the 5V
rail? Not likely, but check anyways. Disconnect them and repeat z
test.

- Identify the 5V regulator, if present. Remove and repeat z test.

- Apply 5V current-limited to 100-1000mA. Check mV appearing on 5V
tracking, looking for lowest values and finger components ( IC and
caps ) for temperature rise.

You are losing the patient.

RL

blown board snaffu, where to start ?
 

legg wrote:
On Tue, 6 Nov 2007 07:25:01 -0500, "robb" wrote:

this is the board where the 32 V line shorted with 5V line at the
green ribbon connector near transformer and only blew center
busman fuse . i get continuity between 5v and 0V ref and now i
need some advice where to start looking for problems or some
methodology on what to do (pull ICs, etc)

and of course no schematic, i am trying to map the power section
now


Pull connectors. Repeat 5-0V z test at both ends.

On the end with zero ohms:

- Is there anything that looks like a zener or crowbar across the 5V
rail? Not likely, but check anyways. Disconnect them and repeat z
test.

- Identify the 5V regulator, if present. Remove and repeat z test.

- Apply 5V current-limited to 100-1000mA. Check mV appearing on 5V
tracking, looking for lowest values and finger components ( IC and
caps ) for temperature rise.


Yep, that's how it's done. If you have access to an infrared imager or
camera that can greatly speed up the search.


You are losing the patient.


There is always hope ;-)

--
Regards, Joerg

http://www.analogconsultants.com/

blown board snaffu, where to start ?
 

"legg" wrote in message
...
On Tue, 6 Nov 2007 07:25:01 -0500, "robb"
wrote:

this is the board where the 32 V line shorted with 5V line at
the
green ribbon connector near transformer and only blew center
busman fuse . i get continuity between 5v and 0V ref and now i
need some advice where to start looking for problems or some
methodology on what to do (pull ICs, etc)

and of course no schematic, i am trying to map the power
section
now


Pull connectors. Repeat 5-0V z test at both ends.

On the end with zero ohms:

- Is there anything that looks like a zener or crowbar across
the 5V
rail? Not likely, but check anyways. Disconnect them and repeat
z
test.

- Identify the 5V regulator, if present. Remove and repeat z
test.

- Apply 5V current-limited to 100-1000mA. Check mV appearing on
5V
tracking, looking for lowest values and finger components ( IC
and
caps ) for temperature rise.

Thanks for help RL,

i forgot to thank you earlier so tanks for that help.
i followed your advice to get to my current status.

looks like the ROM and 8031 MCU are sacrificial toast
thanks again,
rob

blown board snaffu, where to start ?
 

"Joerg" wrote in message
t...
legg wrote:
On Tue, 6 Nov 2007 07:25:01 -0500, "robb"
wrote:

this is the board where the 32 V line shorted with 5V line
at the
green ribbon connector near transformer and only blew center
busman fuse . i get continuity between 5v and 0V ref and now
i
need some advice where to start looking for problems or some
methodology on what to do (pull ICs, etc)

and of course no schematic, i am trying to map the power
section
now


Pull connectors. Repeat 5-0V z test at both ends.

On the end with zero ohms:
- Is there anything that looks like a zener or crowbar across
the 5V
rail? Not likely, but check anyways. Disconnect them and
repeat z
test.

- Identify the 5V regulator, if present. Remove and repeat z
test.

- Apply 5V current-limited to 100-1000mA. Check mV appearing
on 5V
tracking, looking for lowest values and finger components (
IC and
caps ) for temperature rise.

Yep, that's how it's done. If you have access to an infrared
imager or
camera that can greatly speed up the search.

There is always hope ;-)

Thans Joerg,

The only thermal imager i had was a cheapie and inaccurate
**finger** but i had 8 of those in case any lost sensitivity and
two backup *thumbs* in case the fingers blew a sensor :)

forgot to thanks you earlier , thnaks for help,
robb